Benzyl methacrylate (BzMA) is polymerized using a poly(lauryl methacrylate) macromolecular chain transfer agent (PLMA macro-CTA) using reversible addition–fragmentation chain transfer (RAFT) polymerization at 70 °C in n-dodecane. This choice of solvent leads to an efficient dispersion polymerization, with polymerization-induced self-assembly (PISA) occurring via the growing PBzMA block to produce a range of PLMA–PBzMA diblock copolymer nano-objects, including spheres, worms, and vesicles. In the present study, particular attention is paid to the worm phase, which forms soft free-standing gels at 20 °C due to multiple inter-worm contacts. Such worm gels exhibit thermo-responsive behavior: heating above 50 °C causes degelation due to the onset of a worm-to-sphere transition.

Degelation occurs because isotropic spheres interact with each other much less efficiently than the highly anisotropic worms. This worm-to-sphere thermal transition is essentially irreversible on heating a dilute solution (0.10% w/w) but is more or less reversible on heating a more concentrated dispersion (20% w/w). The relatively low volatility of n-dodecane facilitates variable-temperature rheological studies, which are consistent with eventual reconstitution of the worm phase on cooling to 20 °C. Variable-temperature 1H NMR studies conducted in d 26-dodecane confirm partial solvation of the PBzMA block at elevated temperature: surface plasticization of the worm cores is invoked to account for the observed change in morphology, because this is sufficient to increase the copolymer curvature and hence induce a worm-to-sphere transition. Small-angle X-ray scattering and TEM are used to investigate the structural changes that occur during the worm-to-sphere-to-worm thermal cycle; experiments conducted at 1.0 and 5.0% w/w demonstrate the concentration-dependent (ir)reversibility of these morphological transitions. It is well-known that self-assembly of AB diblock copolymers occurs in appropriate selective solvents.

Coefficient DR—an effect that is absent at mean-field level. An alternative closure scheme, based on the necklace approximation, probes the strong coupling behavior of the system and predicts that DR is renormal- ized to zero at a critical. We have imposed an initial condition of zero concentration field. Initial Monogram Wedding Cake Topper Swarovski Crystal Rhinestone Letter on Etsy. Layered Initial Necklace,All 925 sterling silver, double chain, personalized,Monogram,letter A B C D E F G H I J K L M N O P R S T U V W Y Z by potionumber9 on Etsy. Stunning Mass Effect Portraits (And Dragon Age on a Leash).

This is typically conducted in dilute solution (. We and others have recently shown that polymerization-induced self-assembly (PISA) offers a potentially decisive option for the formation of diblock copolymer nano-objects. For example, spherical, worm-like, or vesicular block copolymer morphologies can be efficiently generated directly in either water, alcohol, or n-alkanes at relatively high solids (up to 25%) during the synthesis of the copolymer chains. The worm phase is particularly interesting, because such particles can either act as thickeners or form free-standing gels, depending on the copolymer concentration. Recently, Blanazs et al. Have shown that a semi-concentrated aqueous dispersion of methacrylic diblock copolymer worms undergoes a worm-to-sphere morphological transition on cooling from 20 to 5 °C.

This results in thermo-reversible degelation, which allows facile sterilization via cold ultrafiltration because this protocol removes any micrometer-sized bacteria that may be present. Such worm gels are also highly biocompatible, and both the gel strength and the critical gelation temperature can be tuned; thus they are expected to have biomedical applications in the context of cell storage media. In the present work, we revisit a new RAFT non-aqueous dispersion polymerization formulation that enables a range of poly(lauryl methacrylate)–poly(benzyl methacrylate) [PLMA–PBzMA] diblock copolymer nano-objects to be prepared in n-heptane. Working at a fixed solids concentration of 20% w/w in n-dodecane, a phase diagram has been constructed that reveals the effect of varying the mean degrees of polymerization (DP) of the stabilizer and core-forming blocks on the final copolymer morphology. Using n-dodecane in place of n-heptane facilitates studies of the worm gel phase, because the problem of in situ solvent evaporation is avoided. Furthermore, we demonstrate that PLMA-PBzMA diblock copolymer worm gels undergo reversible degelation on heating (see Figure ). Transmission electron microscopy (TEM), dynamic light scattering (DLS), gel rheology, variable temperature 1H NMR spectroscopy, and small-angle X-ray scattering (SAXS) are used to characterize this phase transition, and a physical mechanism for worm disintegration is suggested.

(A) RAFT synthesis of poly(lauryl methacrylate) (PLMA) macro-CTA via RAFT solution polymerization in toluene at 70 °C, followed by RAFT dispersion polymerization of benzyl methacrylate (BzMA) in n-dodecane at 70 °C. (B) Schematic representation of the change in morphology that occurs on increasing the PBzMA target degree of polymerization when using a relatively short PLMA macro-CTA. (C) Thermo-responsive solution behavior exhibited by 20% w/w PLMA 16–PBzMA 37 diblock copolymer nanoparticles in n-dodecane.

A free-standing gel is formed at 20 °C, which becomes a free-flowing solution when heated to 70 °C (see main text for an explanation of this phase transition). The synthesis of PLMA macro-CTAs has been described in detail elsewhere, and therefore only one representative formulation is briefly discussed here.

A typical synthesis of PLMA 16 macro-CTA was conducted as follows. A 100 mL round-bottomed flask was charged with lauryl methacrylate (LMA; 30 g; 118 mmol), cumyl dithiobenzoate (CDB; 3.22 g; 11.8 mmol), 2,2′-azobis(isobutyronitrile) (AIBN; 387 mg, 2.37 mmol; CDB/AIBN molar ratio = 5.0), and toluene (50.4 g). The sealed reaction vessel was purged with nitrogen and placed in a preheated oil bath at 70 °C for 11 h. The resulting PLMA (LMA conversion = 79%; M n = 4900 g mol –1, M w = 5400 g mol –1, M w/ M n = 1.19) was purified by precipitation into excess methanol. The mean degree of polymerization (DP) of this macro-CTA was calculated to be 16 using 1H NMR spectroscopy by comparing the integrated signals corresponding to the CDB aromatic protons at 7.1–8.1 ppm to that assigned to the two oxymethylene protons of PLMA at 3.7–4.2 ppm. A typical RAFT non-aqueous dispersion polymerization synthesis of PLMA 16–PBzMA 37 diblock copolymer worms at 20% w/w solids was carried out as follows.

Benzyl methacrylate (BzMA; 0.450 g; 2.55 mmol), AIBN initiator (4.50 mg; 0.027 mmol; dissolved at 1.0% w/w in BzMA), and PLMA 16 macro-CTA (0.30 g; 1.10 mmol; macro-CTA/initiator molar ratio = 5.0) were dissolved in n-dodecane (4.0 mL; 3.00 g). The reaction mixture was sealed in a 10 mL round-bottomed flask and purged with nitrogen gas for 25 min while being immersed in an ice bath to reduce solvent evaporation. The deoxygenated solution was then placed in a preheated oil bath at 70 °C for 16 h (final BzMA conversion = 98%; M n = 10 800 g mol –1, M w/ M n = 1.25). The same diblock copolymer formulation was scaled up for rheological studies.

In further syntheses, the mean DP of the PBzMA block was systematically varied by adjusting the amount of added BzMA monomer under otherwise identical reaction conditions. Molecular weight distributions were assessed by gel permeation chromatography (GPC) using THF eluent. The GPC setup comprised two 5 μm (30 cm) Mixed C columns, a WellChrom K-2301 refractive index detector operating at 950 ± 30 nm, a Precision detector PD 2020 light scattering detector (with scattering angles of 90° and 15°), and a BV400RT solution viscosity detector. The mobile phase contained 2.0% v/v triethylamine and 0.05% w/v butylhydroxytoluene, and the flow rate was fixed at 1.0 mL min –1.

A series of 10 near-monodisperse poly(methyl methacrylate) standards ( M p values ranging from 1280 to 330 000 g mol –1) were used for calibration. 1H NMR spectra were recorded in either CD 2Cl 2 or CDCl 3 using a Bruker AV1-400 or AV1-250 MHz spectrometer. Typically 64 scans were averaged per spectrum. For variable-temperature 1H NMR studies, 0.50 mL of a 20% w/w dispersion of PLMA 16–PBzMA 37 worms was diluted to 10% w/w using n-dodecane (0.50 mL) prior to centrifugation at 8000 rpm for 8 h. The sedimented worms were then redispersed with the aid of an ultrasonic bath using d 26-dodecane (2.0 mL) to produce a 5.0% w/w dispersion. 1H NMR spectra were recorded at various temperatures ranging from 25 to 149 °C (32 scans per spectrum, delay time = 0.10 s) using a Bruker AV1-500 MHz spectrometer. Dynamic light scattering (DLS) studies were performed using a Zetasizer Nano-ZS instrument (Malvern Instruments, UK) at a fixed scattering angle of 173°.

Copolymer dispersions were diluted in n-dodecane prior to light scattering studies at 25 °C. Temperature-dependent DLS studies were performed using the same Zetasizer Nano-ZS instrument, which was equipped with a Peltier cell. Copolymer dispersions were diluted in n-dodecane and equilibrated for 5 min at 10 °C intervals in a 20 °C–90 °C–20 °C thermal cycle. In both sets of experiments, the intensity-average diameter and polydispersity of the diblock copolymer particles were calculated at a given temperature by cumulants analysis of the experimental correlation function using Dispersion Technology Software version 6.20.

Data were averaged over 13 runs each of 30 s duration. Transmission electron microscopy (TEM) studies were conducted using a Philips CM 100 instrument operating at 100 kV and equipped with a Gatan 1 k CCD camera. Diluted block copolymer solutions (. An AR-G2 rheometer equipped with a variable-temperature Peltier plate and a 40 mL 2° aluminum cone was used for all experiments. The loss and storage moduli ( G″ and G′, respectively) were measured as a function of temperature at a heating rate of 1.0 °C per minute, a fixed strain of 1.0%, and an angular frequency of 10 rad s –1 so as to assess the gel strength and critical gelation temperature (CGT). During temperature sweeps, the temperature was varied at 5 °C intervals, with an equilibration time of 5 min being allowed prior to each measurement. A frequency sweep from 0.1 to 100 rad s –1 was conducted at 20 °C using a fixed strain of 1.0% and an equilibration time of 1 min between each measurement.

In all cases, the sample gap was 58 μm. SAXS patterns were collected at a synchrotron source (ESRF, station BM26, Grenoble, France) using monochromatic X-ray radiation (wavelength λ = 0.1 nm, with q ranging from 0.023 to 1.3 nm –1, where q = 4π sin θ/λ is the length of the scattering vector and θ is one-half of the scattering angle) and a 2D Pilatus 1M CCD detector. Glass capillaries of 2 mm diameter were used as a sample holder. Time-resolved SAXS patterns were recorded at a rate of 2 frames per minute during thermal cycles performed on the samples (heating from 20 °C to 160 °C at a rate of 5 °C min –1, equilibrating for 5 min, and then cooling back to 20 °C at 5 °C min –1).

The sample temperature was controlled by a heating/cooling capillary holding stage (Linkam Scientific Instruments Ltd., Tadworth, England). Scattering data were reduced by Nika SAS macros for Igor Pro (integration, normalization, and background subtraction) and were further analyzed using Irena SAS macros for Igor Pro.

Glassy carbon was used for the absolute intensity calibration. Measurements were conducted on 1.0% w/w and 5.0% w/w dispersions of PLMA 16–PBzMA 37 particles in n-dodecane. RAFT solution polymerization of LMA was conducted in toluene at 70 °C.

This afforded low polydispersity PLMA macro-CTAs in high yield with a mean degree of polymerization (DP) of 16, 18, or 21 (see Table S1). Each macro-CTA was formed using cumyl dithiobenzoate as a CTA. In all LMA polymerizations, the reaction was quenched at 73%–84% conversion, so as to avoid monomer-starved conditions and hence ensure retention of the RAFT end-groups. This is a prerequisite for high blocking efficiencies and hence well-defined PLMA–PBzMA diblock copolymers.

Each PLMA macro-CTA had a polydispersity ( M w/ M n) of less than 1.25, which is consistent with previous studies reporting well-controlled RAFT syntheses. BzMA monomer was polymerized using each of the relatively short, low polydispersity PLMA macro-CTAs (DP = 16, 18, or 21) in turn via RAFT dispersion polymerization in n-dodecane to generate a series of well-defined PLMA–PBzMA diblock copolymers at 20% w/w solids (see Figure S1 and Table S2).

In all cases, more than 94% BzMA conversion was achieved within 16 h at 70 °C, as judged by 1H NMR spectroscopy. TEM studies indicated that spherical, worm-like, or vesicular morphologies can be accessed when chain-extending PLMA 16 and PLMA 18 macro-CTAs (see Figure ). However, only spherical morphologies were obtained when using a longer PLMA 21 macro-CTA. This indicates that the upper limit degree of polymerization for the stabilizer block to form higher order morphologies (i.e., either worms or vesicles) is relatively low for this PLMA–PBzMA/ n-dodecane formulation. We reported similar results for the synthesis of the same diblock copolymer via RAFT dispersion polymerization in n-heptane at 90 °C. In this earlier study, a detailed phase diagram was constructed for a fixed PLMA stabilizer DP of 17, with variables being the mean DP of the PBzMA core-forming block and the total solids at which the syntheses were conducted. It was shown that lower concentrations (≤15% w/w solids) typically led to mixed phases, with the formation of pure phases requiring somewhat higher concentrations (>17.5% w/w).

Sahte Lise Karnesi Yapma Program?. Thus, in the present work, we chose to construct a different phase diagram, whereby all syntheses were conducted at 20% w/w solids and the two variables were the mean DPs of the PLMA and PBzMA blocks. Three PLMA macro-CTAs with DPs of 16, 18, and 21 were utilized, while the DP of the PBzMA block was systematically varied from 20 to 80 (see Figure and Table S2).

As anticipated, the worm phase region is relatively narrow (e.g., less than 10 BzMA units for PLMA 18–PBzMA x). The worms have relatively well-defined mean widths (10–20 nm), but are rather polydisperse in length (100–1000 nm).

This suggests that the mechanism of worm formation during the RAFT polymerization of BzMA most likely involves the one-dimensional aggregation and fusion of monomer-swollen spheres. Similar observations have been reported for various other diblock copolymer worm systems in the literature. Phase diagram constructed for PLMA x–PBzMA y diblock copolymer nanoparticles prepared by RAFT dispersion polymerization of BzMA in n-dodecane at 20% w/w solids using AIBN at 70 °C (PLMA/AIBN molar ratio = 5.0). The post mortem diblock copolymer morphologies were determined by TEM.

Note that higher order morphologies (worms and vesicles) can be obtained when using PLMA 16 and PLMA 18 macro-CTAs, but not when using the PLMA 21 macro-CTA. TEM images (a), (b), and (c) correspond to examples of the three pure morphologies (spheres, worms, or vesicles), respectively, and the individual block copolymer compositions are indicated within the phase diagram. Focusing on the worm phase boundary, we previously reported that PLMA 17–PBzMA x worms were obtained in n-heptane at 20% w/w solids when x = 50–60. Inspecting Figure, the worm phase appears to be located within x = 35–40 for this hypothetical diblock composition at 20% w/w in n-dodecane. This implies a significant shift in the worm phase boundaries on switching from n-heptane to n-dodecane, which in turn suggests that each n-alkane solvent requires the construction of a detailed phase diagram to ensure reproducible targeting of pure diblock copolymer morphologies. Variable-temperature dynamic light scattering (DLS) studies showing the variation of hydrodynamic diameter (blue ▲) and polydispersity (red ■) for a 0.10% w/w PLMA 16–PBzMA 37 dispersion in n-dodecane on heating from 20 to 90 °C (filled symbols) and on cooling from 90 to 20 °C (open symbols).

Representative transmission electron microscopy (TEM) images obtained for the same dilute dispersion are shown as insets. These data confirm the irreversible nature of the worm-to-sphere transition that occurs on heating PLMA 16–PBzMA 37 under these conditions. To examine the physical mechanism of degelation, DLS studies were conducted on a highly dilute (0.10% w/w) PLMA 16–PBzMA 37 worm dispersion in n-dodecane (see Figure ). An apparent sphere-equivalent hydrodynamic diameter of 170 nm (DLS polydispersity = 0.37) was observed at 20 °C, which is consistent with the presence of worm-like particles. However, heating this dilute dispersion resulted in a dramatic reduction in the apparent hydrodynamic diameter, from 167 nm at 60 °C to around 60 nm at 90 °C. The nanoparticle polydispersity at 90 °C is also reduced to around 0.14, which is characteristic of spheres rather than worms.

The dimensions of these particles remained relatively constant on cooling to 20 °C (hydrodynamic diameter = 46 nm; DLS polydispersity = 0.13), suggesting that this thermal transition is essentially irreversible when conducted in sufficiently dilute solution. TEM studies of the same dilute dispersion conducted before and after the 20–90–20 °C thermal cycle confirmed an irreversible change in morphology for the PLMA 16–PBzMA 37 particles (at least on a time scale of several hours). A well-defined worm morphology is observed at 20 °C before the heating cycle (see image (a) in Figure ), whereas a predominantly spherical morphology exists at 20 °C after the heating cycle (see image (b) in Figure ). Presumably, degelation occurs on heating once a critical fraction of worms has been converted into spheres, because this reduction in particle anisotropy inevitably leads to a catastrophic reduction in the number of inter-particle contacts. Rheological studies were performed on a representative worm gel (20% w/w PLMA 16–PBzMA 37 in n-dodecane).

At 20 °C, G′ was found to be relatively independent of frequency (see Figure S3), indicating that the worm gel can be considered a “true” gel. Additionally, variable-temperature studies were conducted to characterize the thermo-responsive behavior of this gel.

The critical gelation temperature (CGT) is defined as the point at which the G′ and G″ curves cross over. On heating to 47 °C, a CGT was observed at approximately 47 °C (see Figure ).

The gel had reformed at 20 °C, with the G′ and G″ curves intersecting at approximately the same CGT during the cooling cycle. This suggests a reversible thermal transition.

However, the final gel strength ( G′ ≈ 87 Pa) was substantially reduced when compared to the original gel strength ( G′ ≈ 2300 Pa), which indicates significant hysteresis under these conditions. It is perhaps noteworthy that the critical temperature (>70 °C) required for the worm-to-sphere transition suggested by the DLS studies shown in Figure is somewhat higher than that indicated by the rheological studies (CGT ≈ 47 °C) shown in Figure. It is possible that this discrepancy may be simply the result of the differing copolymer concentrations (0.10% w/w for DLS vs 20% w/w for rheology). However, the mean particle size reported by DLS will only decrease significantly once almost all of the worms have been converted into spheres, because the scattered light intensity is proportional to the sixth power of the particle dimensions. In contrast, it is likely that only a minor fraction of worms need to be converted into spheres to cause degelation in the rheology studies. Thus, these two techniques are understandably sensitive to different stages of the worm-to-sphere transition.

Systematic dilution of a 20% w/w PLMA 16–PBzMA 37 worm gel in n-dodecane was undertaken to estimate the critical gelation concentration (CGC). This dispersion failed a tube inversion test at approximately 11% w/w, indicating degelation at this concentration. This is significantly higher than the CGC of approximately 3–4% w/w observed for aqueous diblock copolymer worm gels reported by Verber et al.

One possible explanation for this unexpected difference is that the aqueous worms may have a significantly greater mean contour length than the worms described herein. TEM studies of the original 20% w/w PLMA 16–PBzMA 37 worm gel (after dilution of this dispersion to 0.01% w/w using n-dodecane) reveal a pure worm phase at 20 °C, as expected (see Figure A). Heating this 20% w/w worm gel to 90 °C causes degelation, indicating a worm-to-sphere transition. Cooling this concentrated dispersion to 20 °C led to regelation. After dilution to 0.01% w/w solids, TEM studies confirmed the reformation of worms, albeit with a minor population of spheres (see Figure B). Thus, the worm-to-sphere thermal transition appears to be reasonably reversible for concentrated copolymer dispersions, in marked contrast to the irreversible behavior observed for highly dilute dispersions (see Figure ). In unpublished work, we have recently observed a similarly strong concentration dependence for aqueous diblock copolymer worm gels/dispersions.

Presumably, this reflects the highly cooperative nature of the sphere-to-worm transition, which requires the self-assembly of many spheres to form a single worm. Such multiple fusion events are much less likely to occur for highly dilute dispersions, at least within normal experimental time scales (hours/days).

Variable-temperature 1H NMR spectroscopy studies were undertaken using d 26-dodecane to examine the molecular basis for the worm-to-sphere transition. On heating above 70 °C, the aromatic signals assigned to the BzMA residues at 6.7–7.4 ppm become increasingly intense relative to the two oxyethylene protons assigned to the PLMA block at 4.0 ppm (see Figure ). This spectral change proved to be reversible on cooling and suggests solvent plasticization of the core-forming block at elevated temperature. Similar effects have been reported by Price and co-workers for polystyrene-core diblock copolymer micelles dispersed in n-octane. The same workers also reported an irreversible worm-to-sphere transition on heating a dilute dispersion of polystyrene–polyisoprene diblock copolymer worms in N, N′-dimethylacetamide. However, no attempt was made to study this thermal transition for relatively concentrated copolymer gels/dispersions, where the change in morphology becomes more or less reversible (as in the present work).

Thus, these variable-temperature 1H NMR studies confirm that the PBzMA block becomes partially plasticized in hot d 26-dodecane, which must cause a subtle shift in the relative volume fractions of the stabilizer and core-forming blocks. Because the worm phase occupies only a narrow phase region, this in turn induces a morphological transition. However, these observations immediately suggest an apparent paradox.

Assuming a constant degree of solvation for the PLMA stabilizer chains, greater solvation of the core-forming PBzMA block due to its plasticization would be expected to increase its relative volume fraction, and so reduce the molecular curvature of the copolymer chains. This should produce a worm-to-vesicle transition, rather than the worm-to-sphere transition that is actually observed (see Figure ). We believe that this apparent discrepancy can be explained as follows. The partial solvation of the core-forming PBzMA block indicated by the variable-temperature 1H NMR studies most likely involves surface plasticization of the sterically stabilized worms. Thus, the ingress of solvent into the worms leads to those segments of the core-forming PBzMA block that are closest to the PLMA stabilizer chains becoming preferentially solvated.

This causes an increase in the effective stabilizer block DP (and a concomitant reduction in the effective core-forming block DP) and hence higher molecular curvature for the diblock copolymer chains. This hypothesis is physically realistic and accounts for the observed worm-to-sphere transition; it is supported by 1H NMR studies of a polystyrene-based diblock copolymer in d 18-octane reported by Heatley and co-workers. Surface plasticization can also be invoked to account for the worm-to-sphere transition observed for the aqueous worm gel formulation previously reported by Blanazs et al.]. More recently, LaRue and co-workers used a combined theoretical and experimental approach to explore the thermally induced worm-to-sphere transition exhibited by a polystyrene–polyisoprene diblock copolymer in n-heptane, which is a selective solvent for the polyisoprene block. Static light scattering (SLS) and atomic force microscopy (AFM) were used to characterize this transition, which was described as “reversible”. However, although the worm-to-sphere transition induced by heating from 25 to 35 °C was relatively fast, the reported SLS data actually showed that the sphere-to-worm transition was still substantially incomplete even after 36 days at 25 °C. Bearing in mind the DLS studies reported in the present work, this is almost certainly because of the dilute solution conditions (.

In a typical I( q) versus q plot, the low q (Guinier) region is particularly useful for assessing the particle morphology. A gradient of zero indicates a spherical morphology, whereas a negative gradient of unity is obtained for rods. In the present study, the PLMA 16–PBzMA 37 worms are highly anisotropic but relatively flexible, so a negative gradient close to (but less than) unity is expected. Previously, Blanazs et al. Utilized SAXS to study the thermally induced worm-to-sphere transition for PGMA–PHPMA diblock copolymer nanoparticles in aqueous solution and observed excellent reversibility at a copolymer concentration of 10% w/w.

SAXS patterns obtained for PLMA 16–PBzMA 37 diblock copolymer nano-objects in n-dodecane as a function of temperature are shown in Figure A. At 20 °C, the scattering pattern obtained at 5.0% w/w copolymer has a negative gradient slightly lower than unity in the low q region and also a local minimum in intensity at high q (∼0.50 nm –1), indicating a mean worm cross-section of approximately 13 nm. Heating to 160 °C leads to a substantial change in this SAXS pattern: the gradient at low q tends to zero, and the feature at q ≈ 0.50 nm –1 disappears. On returning to 20 °C, a negative gradient at low q is again observed (albeit marginally lower than the original gradient), and the minimum at q ≈ 0.50 nm –1 is almost completely recovered. Figure B shows SAXS data obtained for 1.0% w/w PLMA 16–PBzMA 37 particles on heating from 20 °C to 160 °C.

At 20 °C, the scattering pattern can be analyzed using the aforementioned worm model. Table shows the key parameters obtained from the data fit using this model.

Notably, the total worm cross-section is 15.4 nm and the worm contour length exceeds 600 nm, indicating highly anisotropic particles with a mean aspect ratio of more than 39; see Table. These values correlate well with TEM observations (see Figure A). Another interesting observation is that these PLMA 16–PBzMA 37 worms are relatively stiff, because their Kuhn length (160 nm) is an order of magnitude greater than the total worm cross-section. This is consistent with the bottle brush-like structure of the PLMA stabilizer block.

Furthermore, both 1H NMR and SAXS studies indicate little or no solvation of the worm core-forming PBzMA block at 20 °C (see Figure and Table, final column). The radius of gyration of 1.3 nm for the coronal PLMA block indicated by SAXS is close to that estimated on the basis of the mean DP of the PLMA block (∼1.0 nm; see the ). On heating to 90 °C, the mean worm cross-section does not vary (although the minimum at q ≈ 0.50 nm –1 virtually disappears). However, the worm contour length is reduced from more than 600 to ∼350 nm, indicating partial worm disintegration. At this elevated temperature, the degree of core solvation ( x sol) increases to 0.29, suggesting ingress of n-dodecane into the PBzMA cores (also indicated by the 1H NMR studies shown in Figure ).

On further heating to 160 °C, the SAXS pattern can now only be satisfactorily fitted using parameters that approximate to isotropic particles (i.e., a total worm cross-section = 15.1 nm, worm contour length = 17.3 nm, and worm Kuhn length = 16.8 nm). This indicates that the vast majority of particles in the dispersion are now actually spherical micelles, with only a relatively minor population of worms remaining at 160 °C (as indicated by the upturn in the scattering curve at very low q).

At this temperature, the degree of solvation in the cores of these copolymer particles is relatively high ( x sol = 0.48), which supports our hypothesis that surface plasticization of the PBzMA core-forming block is a key factor for the conversion of worms into spheres. (a) Representative SAXS patterns recorded for 5.0 and 1.0% w/w PLMA 16–PBzMA 37 copolymer dispersions in n-dodecane recorded during a 20–160–20 °C thermal cycle. The 1.0% w/w data are offset by a factor of 0.1 for clarity. Gradients of zero and negative unity (dashed gray lines) are also shown as a guide to the eye.

(b) Representative SAXS patterns (symbols) for the same 1.0% w/w PLMA 16–PBzMA 37 copolymer dispersion in n-dodecane recorded during heating from 20 °C to 160 °C. In this case, SAXS patterns are offset a factor of 0.1 (90 °C) and 0.01 (160 °C) for clarity, fits to the data (solid lines) are shown, and the results of this analysis are summarized in Table. The inset shows all three scattering patterns plotted on the same scale. It is emphasized that the worm-to-sphere transition described herein, which occurs on heating a worm dispersion in an n-alkane solvent, is wholly complementary to that previously reported for aqueous worms, which form spheres on cooling.

This is presumably related to the well-known upper critical solution temperature (UCST) effect for hydrophobic polymers in organic solvents (e.g., polystyrene in cyclohexane), as opposed to the lower critical solution temperature (LCST) effect that is widely reported for many non-ionic water-soluble polymers in aqueous solution. Finally, in view of the scalable nature of RAFT polymerization chemistry, such thermo-sensitive block copolymer formulations may offer potential applications as viscosity modifiers (thickeners) or lubricants for next-generation engine oils. In summary, PLMA–PBzMA diblock copolymer spheres, worms, or vesicles can be readily prepared via polymerization-induced self-assembly at 20% w/w solids in n-dodecane at 70 °C, provided that the mean degree of polymerization of the PLMA stabilizer block is relatively low. The worms form free-standing gels at 20 °C, but undergo degelation on heating via a worm-to-sphere order–order transition. Variable-temperature 1H NMR and SAXS studies indicate that this is the result of a subtle change in the relative volume fractions occupied by the stabilizer and core-forming blocks caused by surface plasticization of the core-forming block. This thermally induced change in copolymer morphology is essentially irreversible on an experimental time scale of hours when conducted in highly dilute solution (∼0.1% w/w), as judged by DLS and TEM studies. This is because the self-assembly of each worm from the fusion of multiple spheres is highly inefficient under these conditions.

In contrast, much more reversible behavior is observed at higher copolymer concentrations (5.0–20% w/w), as judged by 1H NMR spectroscopy, TEM, gel rheology, and SAXS studies. However, the latter technique indicates a significant reduction in mean contour length for the reformed worms, which is consistent with the reduced gel strength observed for the reconstituted worm gel as judged by gel rheology. • • • • • • • • Acknowledgment Susan Bradshaw is thanked for her assistance with the variable-temperature 1H NMR studies. EPSRC (EP/J007846/1) is acknowledged for providing postdoctoral support for L.A.F., and The University of Sheffield is thanked for funding M.J.D. Also acknowledges an ERC Advanced Investigator grant (PISA 320372). We are grateful to ESRF for providing synchrotron beam-time and thank the personnel of BM26 for their assistance. • • • • • • • • • References This article references 71 other publications.

Vesicles are microscopic sacs that enclose a vol. With a molecularly thin membrane. The membranes are generally self-directed assemblies of amphiphilic mols. With a dual hydrophilic-hydrophobic character. Amphiphiles form vesicles central to cell function and are principally lipids of mol. Less than 1 kDa. Block copolymers that mimic lipid amphiphilicity can also self-assemble into vesicles in dil.

Soln., but polymer mol. Can be orders of magnitude greater than those of lipids. Structural features of vesicles, as well as properties including stability, fluidity, and intermembrane dynamics, are greatly influenced by characteristics of the polymers.

Future applications of polymer vesicles will rely on exploiting unique property-performance relations; but results to date already underscore the fact that biol. Derived vesicles are but a small subset of what is phys. The micellization behavior of styrene (I)-ethylene oxide (II) diblock and triblock copolymers in aq. Is studied via static and dynamic light scattering. There are 2 narrowly distributed populations of particles in the soln.

The sizes of both sets of particles are unchanged in concn. Range of 2 × 10 -5 - 2 × 10-3 g/mL. Fraction of the larger particles decreases with increasing polymer concn. The small particles are regular micelles with an assocn. Of several hundred; the large particles are loose micellar clusters of tens of micelles. The micelle structure is core-shell with a core of I and a shell of II.

The observation by transmission electron microscopy of six different stable aggregate morphologies is reported for the same family of highly asym. Styrene-acrylic acid diblock copolymers prepd. In a low-mol.-wt. Solvent system.

Four of the morphologies consist of spheres, rods, lamellae, and vesicles in aq. Soln., whereas the fifth consists of simple reverse micelle-like aggregates. The sixth consists of up to micrometer-size spheres in aq. That have hydrophilic surfaces and are filled with the reverse micelle-like aggregates. In addn., a needle-like solid, which is highly birefringent, is obtained on drying of aq. Of the spherical micelles. This range of morphologies is believed to be unprecedented for a block copolymer system.

Of ions in micromolar (CaCl2 or HCl) or millimolar (NaCl) concns. Can change the morphol. Of 'crew-cut' aggregates of amphiphilic block copolymers in dil. To spherical, rodlike, and univesicular or lamellar aggregates, an unusual large compd. Vesicle morphol.

Can be obtained from a single block copolymer. Some features of the spontaneously formed large compd.

Vesicles may make them esp. Useful as vehicles for delivering drugs and as models of biol.

Gelation of a dil. Spherical micelle soln. Can also be induced by ions as the result of the formation of a cross-linked 'pearl necklace' morphol. Oxyethylene/oxybutylene block copolymers E41B8, E21B8E21, and B4E40B4 were prepd.

By sequential anionic polymn. And characterized by gel permeation chromatog. And NMR spectroscopy. Their assocn. Behavior in aq. Was investigated by surface tension and static and dynamic light scattering. The diblock copolymer E41B8 and the triblock copolymer E21B8E21 assocd.

By closed processes to form micelles, those of the diblock copolymer being much larger. The triblock copolymer B4E40B4 assocd.

By a process having characteristics of open assocn. Clouding-clearing effect was noted for solns.

Of copolymer E21B8E21. Thermally-reversible sol → gel → sol transitions were obsd. On heating or cooling concd.

Of diblock copolymer E41B8, but concd. Of the two triblock copolymers did not gel.

A review with 192 refs. Discussed the micellization behavior and micelle properties of block copolymers of hydrophilic poly(ethylene oxide) and a hydrophobic poly(alkylene oxide) which can assoc. To form micelles. Copolymers of ethylene oxide with propylene oxide, 1,2-butylene oxide or styrene oxide are considered, including aspects of their prepn. Methods for detn. Conditions for micellization, micelle assocn. And spherical-micelle radius are summarized.

Effects of temp., compn., block length and block architecture (diblock, triblock and cyclic-diblock) are described and, where possible, related to the predictions of theory. Brief consideration is given to the dynamics of micelle formation/dissocn., to cylindrical micelles, and to effects of added salts. Vesicles were made from amphiphilic diblock copolymers and characterized by micromanipulation. Of the specific polymer studied, polyethylene oxide-polyethylethylene (EO40-EE37), is several times greater than that of typical phospholipids in natural membranes. Both the membrane bending and area expansion moduli of electroformed polymersomes (polymer-based liposomes) fell within the range of lipid membrane measurements, but the giant polymersomes proved to be almost an order of magnitude tougher and sustained far greater areal strain before rupture.

The polymersome membrane was also at least 10 times less permeable to water than common phospholipid bilayers. The results suggest a new class of synthetic thin-shelled capsules based on block copolymer chem. Amphiphilic compds. Such as lipids and surfactants are fundamental building blocks of soft matter. We describe expts. With poly(1,2-butadiene-b-ethylene oxide) (PB-PEO) diblock copolymers, which form Y-junctions and three-dimensional networks in water at wt.

Fractions of PEO intermediate to those assocd. With vesicle and wormlike micelle morphologies.

Fragmentation of the network produces a nonergodic array of complex reticulated particles that have been imaged by cryogenic transmission electron microscopy. Data obtained with two sets of PB-PEO compds.

Indicate that this type of self-assembly appears above a crit. These block copolymers represent versatile amphiphiles, mimicking certain low mol. Three-component (surfactant/water/oil) microemulsions, without addn. A low-mol.-wt.

Poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock copolymer contg. Percent PEO forms gigantic wormlike micelles at low concns.

Vesicles made completely from diblock copolymers - polymersomes - can be stably prepd. By a wide range of techniques common to liposomes. Processes such as film rehydration, sonication, and extrusion can generate many-micron giants as well as monodisperse, ∼100 nm vesicles of PEO-PEE (polyethylene oxide-polyethylethylene) or PEO-PBD (polyethylene oxide-polybutadiene).

These thick-walled vesicles of polymer can encapsulate macromols. Just as liposomes can but, unlike many pure liposome systems, these polymersomes exhibit no in-surface thermal transitions and a subpopulation even survive autoclaving. Suspension in blood plasma has no immediate ill-effect on vesicle stability, and neither adhesion nor stimulation of phagocytes are apparent when giant polymersomes are held in direct, protracted contact. Proliferating cells, in addn., are unaffected when cultured for an extended time with an excess of polymersomes.

The effects are consistent with the steric stabilization that PEG-lipid can impart to liposomes, but the present single-component polymersomes are far more stable mech. And are not limited by PEG-driven micellization. The results potentiate a broad new class of technol.

Useful, polymer-based vesicles. Group transfer polymn. (GTP) of four tertiary amine methacrylates, 2-(dimethylamino)ethyl methacrylate (DMA), 2-(diethylamino)ethyl methacrylate (DEA), 2-(diisopropylamino)ethyl methacrylate (DPA) and 2-(N-morpholino)ethyl methacrylate (MEMA) produced a series of near-monodisperse homopolymers (Mw/Mn. Unilamellar polymer vesicles are formed when a block copolymer self-assembles to form a single bilayer structure, with a hydrophobic core and hydrophilic surfaces, and the resulting membrane folds over and rearranges by connecting its edges to enclose a space. The physics of self-assembly tightly specifies the wall thickness of the resulting vesicle, but, both for polymer vesicles and phospholipids, no mechanism strongly selects for the overall size, so the size distribution of vesicles tends to be very polydisperse. We report a method for the prodn.

Of controlled size distributions of micrometer-sized (i.e., giant) vesicles combining the top-down' control of micrometer-sized features (vesicle diam.) by photolithog. And dewetting with the bottom-up' control of nanometer-sized features (membrane thickness) by mol. It enables the spontaneous creation of unilamellar vesicles with a narrow size distribution that could find applications in drug and gene delivery, nano- and micro-reactors, substrates for macromol. And model systems for studies of membrane function. This Progress Report describes the latest advances in vesicles and liposomes.

Recent work on the self-assembly of complex polymer systems shows that the formation of polymer vesicles or closed hull structures is archetypal, leading to fascinating new possibilities and applications in materials science. A general view of the underlying self-assembly mechanisms leading to vesicles and the control of size, shape, and other vesicular properties by physicochem. Means is presented, as background. This is followed by an overview of the recently described new classes of polymer and supramol. Tectons that make vesicle formation a more general phenomenon going beyond just lipids. Finally, the potential applications of vesicles, including nonlipid vesicles, are outlined.

The ability of amphiphilic block copolymers to self-assemble in selective solvents has been widely studied in academia and utilized for various com. The self-assembled polymer vesicle is at the forefront of this nanotechnol. Revolution with seemingly endless possible uses, ranging from biomedical to nanometer-scale enzymic reactors. This review is focused on the inherent advantages in using polymer vesicles over their small mol. Lipid counterparts and the potential applications in biol.

For both drug delivery and synthetic cellular reactors. Block copolymers consist of two or more chem. Different polymers connected by covalent linkages. In soln., repulsion between the blocks leads to a variety of morphologies, which are thermodynamically driven. Polyferrocenyidimethylsilane block copolymers show an unusual propensity to forming cylindrical micelles in soln.

We found that the micelle structure grows epitaxially through the addn. Of more polymer, producing micelles with a narrow size dispersity, in a process analogous to the growth of living polymer. By adding a different block copolymer, we could form co-micelles. We were also able to selectively functionalize different parts of the micelle.

Potential applications for these materials include their use in lithog. Etch resists, in redox-active templates, and as catalytically active metal nanoparticle precursors. Block copolymers consist of two or more chemically distinct polymer segments, or blocks, connected by a covalent link.

In a selective solvent for one of the blocks, core-corona micelle structures are formed. We demonstrate that living polymerizations driven by the epitaxial crystallization of a core-forming metalloblock represent a synthetic tool that can be used to generate complex and hierarchical micelle architectures from diblock copolymers. The use of platelet micelles as initiators enables the formation of scarf-like architectures in which cylindrical micelle tassels of controlled length are grown from specific crystal faces. A similar process enables the fabrication of brushes of cylindrical micelles on a crystalline homopolymer substrate.

Living polymerizations driven by heteroepitaxial growth can also be accomplished and are illustrated by the formation of tri- and pentablock and scarf architectures with cylinder-cylinder and platelet-cylinder connections, respectively, that involve different core-forming metalloblocks. The synthesis and self-assembly of poly(lactide)-b-poly(acrylic acid) and poly(lactide)-b-poly(dimethylaminoethyl acrylate) block copolymers by a combination of ring-opening polymn. And reverse-addn. Fragmentation chain transfer (RAFT) polymn. The self-assembly of block copolymers contg.

Enantiopure homochiral poly(lactide), PLA, by a simple direct dissoln. Results in core-crystn. To afford micelles with cylindrical morphol.

Amorphous atactic PLA cores and conditions that did not promote crystn. Resulted in spherical micelles.

The cylindrical micelles were characterized by transmission electron microscopy (TEM) with cryo-TEM, small angle neutron scattering (SANS) and angular dependent dynamic light scattering (DLS) proving that the cylindrical morphol. Was persistent in soln. Manipulation of the assembly conditions enabled the length and dispersity of the resultant cylindrical micelles to be controlled. Responsiveness is essential to all biol. Systems down to the level of tissues and cells. The intra- and extracellular mechanics of such systems are governed by a series of proteins, such as microtubules, actin, intermediate filaments and collagen. As a general design motif, these proteins self-assemble into helical structures and superstructures that differ in diam.

And persistence length to cover the full mech. Gels of cytoskeletal proteins display particular mech.

Responses (stress stiffening) that until now have been absent in synthetic polymeric and low-molar-mass gels. Here we present synthetic gels that mimic in nearly all aspects gels prepd. From intermediate filaments. They are prepd. From polyisocyanopeptides grafted with oligo(ethylene glycol) side chains.

These responsive polymers possess a stiff and helical architecture, and show a tunable thermal transition where the chains bundle together to generate transparent gels at extremely low concns. Using characterization techniques operating at different length scales (for example, macroscopic rheol.,. Force microscopy and mol. Force spectroscopy) combined with an appropriate theor. Network model, we establish the hierarchical relationship between the bulk mech.

Properties and the single-mol. Our results show that to develop artificial cytoskeletal or extracellular matrix mimics, the essential design parameters are not only the mol.

Stiffness, but also the extent of bundling. In contrast to the peptidic materials, our polyisocyanide polymers are readily modified, giving a starting point for functional biomimetic hydrogels with potentially a wide variety of applications, in particular in the biomedical field.

The authors explore the RAFT synthesis of sterically stabilized PHPMA nanolatexes of 20-100 nm diam. By surfactant-free aq.

Dispersion polymn. Using a poly(glycerol monomethacrylate)-based chain transfer agent(CTA) as the reactive steric stabilizer. Both the latex cores and the steric stabilizer chains of the resulting nanolatexes are highly hydroxylated for this prototype formulation. Electron microscopy and DLS studies confirm relatively narrow particle size distributions in most cases, and the mean latex diam. Can be conveniently controlled over the 20-105 nm range simply by adjusting the target block compn.

In addn., targeting longer core-forming blocks leads to the formation of circa 500 nm block copolymer vesicles, rather than sterically stabilized nanolatexes. This is a potentially very convenient route, since it enables vesicles to be prepd. At relatively high solids. Amphiphilic diblock copolymers composed of two covalently linked, chem. Distinct chains can be considered to be biol.

Mimics of cell membrane-forming lipid mols., but with typically more than an order of magnitude increase in mol. These macromol. Amphiphiles are known to form a wide range of nanostructures (spheres, worms, vesicles, etc.) in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dil. Copolymer solns. (99% monomer conversion) at relatively high solids in purely aq.

Furthermore, careful monitoring of the in situ polymn. By transmission electron microscopy reveals various novel intermediate structures (including branched worms, partially coalesced worms, nascent bilayers, 'octopi', 'jellyfish', and finally pure vesicles) that provide important mechanistic insights regarding the evolution of the particle morphol. During the sphere-to-worm and worm-to-vesicle transitions. This environmentally benign approach (which involves no toxic solvents, is conducted at relatively high solids, and requires no addnl.

Processing) is readily amenable to industrial scale-up, since it is based on com. Available starting materials.

Reversible addn.-fragmentation chain transfer polymn. Has been utilized to polymerize 2-hydroxypropyl methacrylate (HPMA) using a water-sol. Chain transfer agent based on poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC).

A detailed phase diagram has been elucidated for this aq. Dispersion polymn. Formulation that reliably predicts the precise block compns. With well-defined particle morphologies (i.e., pure phases).

Unlike the ad hoc approaches described in the literature, this strategy enables the facile, efficient, and reproducible prepn. Of diblock copolymer spheres, worms, or vesicles directly in concd.

Chain extension of the highly hydrated zwitterionic PMPC block with HPMA in water at 70° produces a hydrophobic poly(2-hydroxypropyl methacrylate) (PHPMA) block, which drives in situ self-assembly to form well-defined diblock copolymer spheres, worms, or vesicles. The final particle morphol. Obtained at full monomer conversion is dictated by (i) the target d.p. Of the PHPMA block and (ii) the total solids concn. At which the HPMA polymn. Is conducted.

Moreover, if the targeted diblock copolymer compn. Corresponds to vesicle phase space at full monomer conversion, the in situ particle morphol. Evolves from spheres to worms to vesicles during the in situ polymn. In the case of PMPC25-PHPMA400 particles, this systematic approach allows the direct, reproducible, and highly efficient prepn. Of either block copolymer vesicles at up to 25% solids or well-defined worms at 16-25% solids in aq.

Polymn.-induced self-assembly (PISA) of poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblocks is conducted using a RAFT aq. Dispersion polymn. Formulation at 70 °C. Several PGMA macromol. Chain transfer agents (macro-CTAs) are chain-extended using a water-miscible monomer (HPMA): the growing PHPMA block becomes increasingly hydrophobic and hence drives in situ self-assembly. The final copolymer morphol.

In such PISA syntheses depends on just three parameters: the mean d.p. (DP) of the PGMA stabilizer block, the mean DP of the PHPMA core-forming block, and the total solids concn. TEM is used to construct detailed diblock copolymer phase diagrams for PGMA DPs of 47, 78, and 112. For the shortest stabilizer block, there is essentially no concn. Dependence: spheres, worms, or vesicles can be obtained even at 10% wt./wt. Solids simply by selecting the DP of the PHPMA block that gives the appropriate mol.

For a PGMA DP of 78, the phase diagram is rich: and the copolymer morphol. Depends strongly on the total solids concn. There is also a narrow region where spheres, worms, and vesicles coexist, which may be due to the effect of polydispersity. For a PGMA112 macro-CTA, the phase diagram is dominated by spherical morphologies.

This is probably because the longer core-forming block DPs required to reduce the mol. Curvature are significantly more dehydrated and hence less mobile, which prevents the in situ evolution of morphol. From spheres to higher order morphologies.

This hypothesis is supported by the observation that addn. Of ethanol to aq. PISA syntheses conducted using the longer macro-CTAs allows access to diblock copolymer worms or vesicles, since this cosolvent solvates the core-forming PHPMA chains and hence increases their mobility at 70 °C.

Elucidation of such phase diagrams is vital to ensure reproducible targeting of pure phases, rather than mixed phases. Benzyl methacrylate (BzMA) is polymd. Via reversible addn.-fragmentation chain transfer (RAFT) chem. Dispersion polymn.

Conditions in ethanol using a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) at 70 °C. In principle, polymn.-induced self-assembly can lead to the formation of either spherical micelles, worm-like micelles, or vesicles, with the preferred morphol.

Being dictated by the hydrophilic-hydrophobic balance of the PDMA-PBzMA diblock copolymer chains. Very high monomer conversions (>99%) are routinely obtained within 24 h as judged by 1H NMR studies.

Moreover, THF GPC analyses confirmed that relatively low polydispersities (Mw/Mn. We report the synthesis of anionic sterically stabilized diblock copolymer nanoparticles via polymn.-induced self-assembly using a RAFT aq.

Dispersion polymn. The anionic steric stabilizer is a macromol. Chain-transfer agent (macro-CTA) based on poly(potassium 3-sulfopropyl methacrylate) (PKSPMA), and the hydrophobic core-forming block is based on poly(2-hydroxypropyl methacrylate) (PHPMA).

The effect of varying synthesis parameters such as the salt concn., solids content, relative block compn., and anionic charge d. In the absence of salt, self-assembly is problematic when using a PKSPMA stabilizer because of lateral repulsion between highly charged anionic chains. However, in the presence of added salt this problem can be overcome by reducing the charge d. Within the coronal stabilizer layer by either (i) statistically copolymg. The KSPMA monomer with a nonionic comonomer (2-hydroxyethyl methacrylate, HEMA) or (ii) using a binary mixt.

Of a PKSPMA macro-CTA and a poly(glycerol monomethacrylate) (PGMA) macro-CTA. These diblock copolymer nanoparticles were analyzed by 1H NMR spectroscopy, gel permeation chromatog. (GPC), dynamic light scattering (DLS), TEM, and aq. NMR studies suggest that the HPMA polymn. Is complete within 2 h at 70°, and DMF GPC anal. Confirms that the resulting diblock copolymers have relatively low polydispersities (Mw/Mn.

Well-defined poly(lauryl methacrylate-benzyl methacrylate) (PLMA-PBzMA) diblock copolymer nanoparticles are prepd. In n-heptane at 90° via reversible addn.-fragmentation chain transfer (RAFT) polymn. Under these conditions, the PLMA macromol. Chain transfer agent (macro-CTA) is sol. In n-heptane, whereas the growing PBzMA block quickly becomes insol.

Thus this dispersion polymn. Formulation leads to polymn.-induced self-assembly (PISA). Using a relatively long PLMA macro-CTA with a mean d.p. (DP) of 37 or higher leads to the formation of well-defined spherical nanoparticles of 41 to 139 nm diam., depending on the DP targeted for the PBzMA block. In contrast, TEM studies confirm that using a relatively short PLMA macro-CTA (DP = 17) enables both worm-like and vesicular morphologies to be produced, in addn. To the spherical phase.

A detailed phase diagram has been elucidated for this more asym. Diblock copolymer formulation, which ensures that each pure phase can be targeted reproducibly. 1H NMR spectroscopy confirmed that high BzMA monomer conversions (>97%) were achieved within 5 h, while GPC studies indicated that reasonably good blocking efficiencies and relatively low diblock copolymer polydispersities (Mw/Mn. A hydrophilic macromol. RAFT (reversible addn.-fragmentation chain transfer) agent (macroRAFT agent) composed of 50 mol% methacrylic acid and 50 mol% poly(ethylene oxide) monomethyl ether methacrylate end-capped by a reactive trithiocarbonate group (P(MAA-co-PEOMA)) was used in the polymn. Of benzyl methacrylate (BzMA) in different media, ethanol-water and 1,4-dioxane-water mixts.

Depending on the solvent compn., the polymn. Showed features of either a dispersion polymn. (monomer sol. In the initial medium) or an emulsion polymn. (monomer insol.

In the initial medium). In all cases, the RAFT mechanism led to the in situ formation of well-defined amphiphilic P(MAA-co-PEOMA)-b-PBzMA block copolymers that self-assembled during the growth step into self-stabilized nano-objects, according to a polymn.-induced micellization process. For a given compn. Of the block copolymer, the final morphol. Depended strongly on the solvent compn. The presence of the org. Co-solvent was favorable to the formation of fibers while an increased amt.

Of water favored the formation of spherical particles. Compared to the ethanol-water system, in which the non-spherical objects existed only above 77-80 vol% of ethanol, in 1,4-dioxane-water mixts. Transition was obsd. At a lower proportion of org. Co-solvent (close to 20 vol%). For a given molar mass of the macroRAFT agent and an increased molar mass of the PBzMA block in a given solvent compn.

(ethanol-water, 95/5, vol./vol.), the morphol. Changed from spheres to fibers and then to large spheres or vesicles. The molar mass window in which fibers were obtained was wider than that obsd. In pure water at pH 5 using the same macroRAFT agent. Zhang et al., Macromols., 2011, 44, 4149.]. Chain transfer agents (Macro-CTAs) were developed for the microwave-assisted pptn.

Of N-isopropylacrylamide. Two types of Macro-CTAs, amphiphilic (Macro-CTA1) and hydrophilic (Macro-CTA2), were studied regarding their activity for the facile formation of nanoparticles and double hydrophilic block copolymers by RAFT processes. While both Macro-CTAs functioned as steric stabilization agents, the variation in their surface activity afforded different levels of control over the resulting nanoparticles in the presence of crosslinkers. The crosslinked nanoparticles produced using the amphiphilic Macro-CTA1 were less uniform than those produced using the fully hydrophilic Macro-CTA2. The nanoparticles spontaneously formed core-shell structures with surface functionalities derived from those of the Macro-CTAs.

In the absence of crosslinkers, both types of Macro-CTAs showed excellent control over the RAFT pptn. Process with well-defined, double hydrophilic block copolymers being obtained. The power of combining microwave irradn. With RAFT procedures was evident in the high efficiency and high solids content of the polymn. In addn., the 'living' nature of the nanoparticles allowed for further copolymn.

Leading to multiresponsive nanostructured hydrogels contg. Surface functional groups, which were used for surface bioconjugation. Self-assembled block copolymer nanofibers are attractive materials for multiple applications. We propose here a novel, very simple and straightforward method to prep. Polymeric nanofibers at high solids contents directly in water. Anatomical Automatic Labeling Manual Woodworkers.

It is based on an aq. Emulsion polymn. Process performed under living radical polymn.

Conditions using the RAFT method. Of styrene in water in the presence of hydrophilic macromol. The RAFT agent was dodecyl trithiocarbonate-end capped acrylic acid-poly(ethylene glycol) Me ether acrylate copolymer. A straightforward approach was developed to synthesize pegylated thermo-responsive core-shell nanoparticles in a min. Of steps, directly in water. It is based on RAFT-controlled radical crosslinking copolymn. Of N,N-diethylacrylamide (DEAAm) and N,N'-methylene bisacrylamide (MBA) in aq.

Dispersion polymn. Because DEAAm is water-sol.

And poly(N,N-diethylacrylamide) (PDEAAm) exhibits a lower crit. At 32°, the initial medium was homogeneous, whereas the polymer formed a sep. Phase at the reaction temp. The first macroRAFT agent was a surface-active trithiocarbonate based on a hydrophilic poly(ethylene oxide) block and a hydrophobic dodecyl chain. It was further extended with N,N-dimethylacrylamide (DMAAm) to target macroRAFT agents with increasing chain length. All macroRAFT agents provided excellent control over the aq. Dispersion homopolymn.

When they were used in the radical crosslinking copolymn. Of DEAAm and MBA, the stability and size of the resulting gel particles were found to depend strongly on the chain length of the macroRAFT agent, on the concns. Of both the monomer and the crosslinker, and on the process (one step or two steps). The best-suited exptl. Conditions to reach thermosensitive hydrogels with nanometric size and well-defined surface properties were detd. A hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) Me ether methacrylate) copolymer with a trithiocarbonate reactive group was used in the free-radical, batch emulsion polymn.

It allowed fast polymns. And high final conversions to be achieved, and the parameters for a good control over the formation of well-defined amphiphilic diblock copolymers were identified.

These diblock copolymers self-assembled in situ into nano-objects of various morphologies upon chain extension. Achieving a good control over the formed diblock copolymers was an important step toward a better understanding of the parameters that affect the shape and size of the self-assembled objects, the ultimate goal being the ability to predict and fine-tune them on purpose.

Well-defined, cholesteryl-based, amphiphilic block copolymer nanofibers have been obtained in a simple, one-pot, ethanol/water dispersion polymn. Process using poly((meth)acrylic acid-co-(poly(ethylene glycol) (meth)acrylate)) copolymers end-functionalized by a reactive trithiocarbonate end-group as macromol. Reversible addn.-fragmentation chain transfer agents (macroRAFT agents). The resulting highly concd. Dispersions were analyzed by TEM (transmission electron microscopy), cryo-TEM, SAXS (small angle X-ray scattering) and SANS (small angle neutron scattering), which allowed the shape and size of the nanoobjects formed in situ to be fully characterized and which revealed moreover the presence of a smectic order in the hydrophobic cores.

Due to this particular substructure, the nanofiber organization was obsd. Over a broad compn. Range of the amphiphilic block copolymers.

A novel strategy for prepn. Of multiple nanostructural materials, which is the creation of such materials directly from controlled radical dispersion polymn.

In one pot, has been developed. In the formation of polymeric nanomaterials, the chain length ratio of the hydrophobic to hydrophilic blocks is altered continuously, which induces two phase transitions, phase sepn. To form spherical micelles and re-organization of the resulting spheres to yield multiple morphologies including nanorods, nanotubes, vesicles and doughnuts.

This is quite different from self-assembly of the block copolymer in a selective solvent, where nature and soly. Parameter of the solvents are changed. In the reversible addn.-fragmentation chain transfer (RAFT) polymn. Of styrene in methanol using poly(4-vinylpyridine) as macro RAFT agent, the resultant polymeric nanomaterials with various morphologies coexisted generally, however, uniform nanowires and vesicles could be prepd. By appropriately selecting concn.

Of monomer and feed ratio, as well as by strict control of reaction conditions. One advantage of this strategy is that the nanomaterials with a concn. As high as 0.5 g mL-1 can be achieved, this provides possibility for studying extensive applications of the various nanomaterials. A facile and feasible strategy for the prepn. Of vesicular morphologies was developed using reversible addn.-fragmentation chain transfer (RAFT) polymn. Of styrene was performed in a selected solvent, methanol, using S-1-dodecyl-S-(α,α'-dimethyl-α'-acetic acid)trithiocarbonate (TC)-terminated poly(4-vinylpyridine) as chain transfer agent and stabilizer.

Various morphologies including spherical vesicles, nanotubes, and compd. Vesicles with different shapes are obtained by changing the feed ratios and reaction conditions. The final nanostructural materials are formed through formation of the block copolymers, self-assembly, and re-organization of the morphol. In a one-pot polymn. The latter two are induced by the propagation of PS blocks. Of nanostructural materials can be performed at a concn.

Higher than 0.5 g/mL-1, thus this method offers a practical approach to prep. Nanostructural materials on a large scale. Various morphologies including spherical micelles, nanowires and vesicles have been prepd. By reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn.

Of styrene (St) in methanol using S-1-dodecyl-S -(α,α'-dimethyl-α'-acetic acid) trithiocarbonate (TC)-terminated poly(ethylene oxide) (PEO-TC) and 2,2'-azobis(isobutyronitrile) (AIBN) as chain transfer agent and initiator, resp. GPC, 1H NMR, TEM and laser light scattering (LLS) were used to track the polymn. The results showed that the block copolymers PEO-b-polystyrene (PEO-b-PS) were formed firstly in homogenous polymer soln., and then the spherical micelles were produced via polymn.-induced self-assembling. Continuous polymn. Of the PS blocks induced the transition of spherical micelles into other morphologies.

The polymn.-induced self-assembling and reorganization (PISR) were induced by chain length ratio increase of PS to PEO blocks. Of St in methanol is also important factor to influence the formation of morphologies. Polymn.-induced self-assembly and re-organization (PISR) was used to prep. Polymeric nanostructured materials with a variety of morphologies. Reversible addn.-fragmentation chain transfer (RAFT) polymn.

Of styrene in a selective solvent, methanol, was carried out using cyanoisopropyl dithiobenzoate-terminated poly(2-dimethylaminoethyl methacrylate) (PDMAEMA-DBT) as the macro chain transfer agent and stabilizer for investigation of the factors influencing the formation of morphologies. Various morphologies, including spherical micelles, nanostrings, vesicles and large compd. Vesicles, with different shapes were obtained by changing the feed ratios and reaction conditions. The sequential morphol. Transitions from spherical micelles to nanostrings, to vesicles and to large compd. Vesicles via increasing the chain length ratio of the hydrophobic block to the hydrophilic one in the same system were obsd.

For the first time. This approach can be performed at a high concn., thus it can be scaled up for the reproducible prepn.

Of nanostructured materials in a relatively high vol. In the past decade, living radical polymn. (LRP) has revolutionized academic research in the fields of free-radical polymn. And materials design.

Sophisticated macromol. Architectures, designed for a variety of applications and end-use properties, can now be synthesized using relatively simple LRP chemistries that do not require stringent oxygen or moisture free environments, subzero reaction temps., or highly purified reagents.

Publications abound not only in the fundamentals of LRP but also its use in designing tailor-made polymers and polymer-hybrid composites. Corporate research organizations have also been actively involved in LRP, with numerous patents being issued annually.

Despite the intense research interest, however, comparatively few products have been commercialized, with high process costs being a primary factor. Free-radical polymns. Are conducted in aq. Dispersions due to significantly lower process costs compared to bulk or soln. Successful widespread commercialization of LRP will be advantaged by the development of waterborne processes yielding aq. Dispersions of nanoparticles.

Conducting LRP within nanoparticles (i.e., using nanoscale particles as self-contained chem. Reactors or 'nanoreactors') enables faster reaction times and if harnessed properly will provide better control over the polymer livingness; it also has the potential in the control of the particle mesostructure and microstructure. Recent progress in LRP dispersions is presented with a discussion of outstanding issues and challenges as well as the outlook for adoption of LRP dispersions by industry. This Perspective describes the recent developments of polymn.-induced self-assembly of amphiphilic block copolymers based on controlled/living free-radical polymn. (CRP) in water. This method relies on the use of a hydrophilic living polymer precursor prepd. Via CRP that is extended with a hydrophobic second block in an aq.

The process thus leads to amphiphilic block copolymers that self-assemble in situ into self-stabilized nano-objects in the frame of an emulsion or dispersion polymn. Depending on the nature and the structure of the so-formed copolymer, not only spherical particles can be achieved but also all morphologies that can be found in the phase diagram of an amphiphilic block copolymer in a selective solvent. This paper focuses mainly on aq. Emulsion or dispersion polymn. And gives an overview of the CRP techniques used, the general conditions, and the morphologies obtained. The RAFT-mediated nonaq.

Dispersion polymn. Of Me acrylate in isododecane, a nonsolvent for poly(Me acrylate), was carried out using two sol.

Poly(2-ethylhexyl acrylate) (I) macromol. RAFT agents, contg. Either a dithiobenzoate reactive function or a trithiocarbonate one. The method produced stable colloidal particles, with hydrodynamic diams. Below 100 nm.

Using I with a dithiobenzoate end group, strong rate retardation and poor control over the polymer chains were obsd. In contrast, when the trithiocarbonate-functionalized I was used, the formation of monodisperse micellar aggregates of well-defined self-assembled block copolymers was obtained with fast polymn. Rates, irresp.

Of the RAFT agent concn. Such differences were explained by the dispersed state of the system rather than by the intrinsic reactivity of the sol. Biocompatible hydrogels have many applications, ranging from contact lenses to tissue engineering scaffolds. In most cases, rigorous sterilization is essential. Herein we show that a biocompatible diblock copolymer forms wormlike micelles via polymn.-induced self-assembly in aq.

At a copolymer concn. Of 10.0 wt./wt.%, interworm entanglements lead to the formation of a free-standing phys. Hydrogel at 21 °C. Occurs on cooling to 4 °C due to an unusual worm-to-sphere order-order transition, as confirmed by rheol., electron microscopy, variable temp. 1H NMR spectroscopy, and scattering studies.

Moreover, this thermo-reversible behavior allows the facile prepn. Of sterile gels, since ultrafiltration of the diblock copolymer nanoparticles in their low-viscosity spherical form at 4 °C efficiently removes micrometer-sized bacteria; regelation occurs at 21 °C as the copolymer chains regain their wormlike morphol. Biocompatibility tests indicate good cell viabilities for these worm gels, which suggest potential biomedical applications.

A series of diblock copolymer worms are prepd. Dispersion polymn. Using reversible addn.-fragmentation chain transfer (RAFT) polymn. More specifically, a poly(glycerol monomethacrylate) (PGMA) RAFT chain transfer agent is used to polymerize a water-miscible monomer, 2-hydroxypropyl methacrylate, at 70 °C. The poly(2-hydroxypropyl methacrylate) (PHPMA) chains become increasingly hydrophobic as they grow, which leads to nanoparticle formation. Careful control of the diblock compn. Is achieved by fixing the mean d.p.

(DP) of the PGMA stabilizer block at 54 and systematically varying the DP of the core-forming PHPMA block. This strategy enables the worm phase space to be targeted reproducibly.

These worms form soft free-standing gels in aq. Due to inter-worm entanglements. Studies enable the influence of the diblock copolymer compn.

On the gel strength, crit. Gelation concn. (CGC) and crit.

Gelation temp. (CGT) to be assessed. In gel strength is obsd.

As the DP of the PHPMA block is increased from 130 to 170. The initial increase is due to longer worms, while the subsequent decrease is assocd. With worm clustering, which leads to more brittle gels.

The gel strength is reduced from approx. 100 Pa to 10 Pa as the copolymer concn. Is lowered from 10 to 5 wt./wt.%, with a CGC being obsd.

At around 3 to 4 wt./wt.%. The CGT is relatively concn.-independent, but sensitive to the diblock copolymer compn.: longer (more PHPMA-rich) chains lead to the CGT being reduced from 20 °C to 7 °C. This is because longer PHPMA blocks require a greater degree of hydration to induce the worm-to-sphere transition, which can only achieved at progressively lower temps. Reversible de-gelation also occurs on cooling, since there can be no entanglements between isotropic particles. This RAFT formulation also provides a rare example of thermo-responsive diblock copolymer worms.

Irena, a tool suite for anal. Of both x-ray and neutron small-angle scattering (SAS) data within the com. Igor Pro application, brings together a comprehensive suite of tools useful for studies in materials science, physics, chem., polymer science and other fields.

To Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dil. Limit using max.

Entropy and other methods, dil. Limit small-angle scattering from multiple noninteracting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye-Bueche model, the reflectivity (x-ray and neutron) using Parratt's formalism, and small-angle diffraction. There are also a no. Of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and x-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export. Calibration of small-angle scattering (SAS) intensity data (measured in terms of the differential scattering cross section per unit sample vol.

Per unit solid angle) is essential for many important aspects of quant. SAS anal., such as obtaining the no. Fraction, and sp. Surface area of the scatterers. It also enables scattering data from different instruments (light, X-ray, or neutron scattering) to be combined, and it can even be useful to detect the existence of artifacts in the exptl. Different primary or secondary calibration methods are available.

In the latter case, abs. Intensity calibration requires a stable artifact with the necessary scattering profile. Glassy carbon has sometimes been selected as this intensity calibration std.

Here we review the spatial homogeneity and temporal stability of one type of com. Available glassy carbon that is being used as an intensity calibration std. Of SAS facilities. We demonstrate that glassy carbon is sufficiently homogeneous and stable during routine use to be relied upon as a suitable std. Intensity calibration of SAS data. The free-radical copolymns.

Oligo(Me methacrylate) (I) with Et acrylate, styrene, Me methacrylate, acrylonitrile, and vinyl acetate were investigated. Incorporation of I into the polymer was obsd. In all cases although the mol. Of the copolymers were substantially lower than those of the homopolymers obtained in the absence of I but under otherwise identical conditions.

These expts., together with a product study of the reactions of I with cyanoisopropyl radicals, showed that the addn. Of free radicals to the double bond of I occurs readily. The sterically hindered radical so formed, however, undergoes facile β-scission, resulting in the termination of chains (chain transfer) in competition with chain propagation.

The implications of these findings to the usefulness of I in the synthesis of graft copolymers and their relevance to the chem. Of free-radical polymns.

When Me methacrylate is employed as a monomer or comonomer are discussed. We present a generalized connectedness percolation theory reduced to a compact form for a large class of anisotropic particle mixts. With variable degrees of connectivity. Even though allowing for an infinite no. Of components, we derive a compact yet exact expression for the mean cluster size of connected particles. We apply our theory to rodlike particles taken as a model for carbon nanotubes and find that the percolation threshold is sensitive to polydispersity in length, diam., and the level of connectivity, which may explain large variations in the exptl.

Values for the elec. Percolation threshold in carbon-nanotube composites. Connectedness percolation threshold depends only on a few moments of the full distribution function. If the distribution function factorizes, then the percolation threshold is raised by the presence of thicker rods, whereas it is lowered by any length polydispersity relative to the one with the same av.

Length and diam. We show that for a given av. Length, a length distribution that is strongly skewed to shorter lengths produces the lowest threshold relative to the equiv.

Monodisperse one. However, if the lengths and diams.

Of the particles are linearly correlated, polydispersity raises the percolation threshold and more so for a more skewed distribution toward smaller lengths. The effect of connectivity polydispersity is studied by considering nonadditive mixts. Of conductive and insulating particles, and we present tentative predictions for the percolation threshold of graphene sheets modeled as perfectly rigid, disklike particles. (c) 2011 American Institute of Physics. A mean-field theory is presented for the percolation behavior of systems of rodlike particles characterized by length polydispersity. An analogy to the problem of site percolation on a modified Bethe lattice is employed to est.

The percolation threshold, percolation probability, and backbone fraction as functions of the rod vol. Fraction and polydispersity. Model calcns. Reveal that the percolation probability and backbone fraction depend sensitively upon the rod length distribution, while the percolation threshold is governed primarily by the wt.-averaged rod length. (c) 2010 American Institute of Physics.

The dynamic structure of micelles formed by a polystyrene-b-poly(ethylene/propylene) block copolymer [25608-79-1] in paraffinic solvents is studied by electron microscopy, photon correlation spectroscopy and 1H and 13C-NMR. In n-octane at 80°.

In higher alkanes, the dissocn. Occurs at increasing temp. With increasing solvent mol.

1H NMR longitudinal and transverse relaxation measurements have been made as a function of temp. For micellar solns. Of a polystyrene-block-poly(ethylene/propylene) copolymer in [2H1]octane. Spin diffusion following selective inversion of protons from 1 component has been used to probe the extent of mixing of the blocks in the interface between the micelle core consisting of slightly swollen polystyrene and the micelle fringe consisting of highly solvated poly(ethylene/propylene). At 80°, a small degree of spin diffusion was detected, indicating that a mixed phase existed. A simple anal. Of the magnitude of the effect showed that ca.

50% of the polystyrene was in the boundary compared with only 3% of the poly(ethylene/propylene). Small angle X-ray scattering (SAXS) is a powerful characterization technique for the anal. Of polymer-silica nanocomposite particles due to their relatively narrow particle size distributions and high electron d. Contrast between the polymer core and the silica shell.

Time-resolved SAXS is used to follow the kinetics of both nanocomposite particle formation (via silica nanoparticle adsorption onto sterically stabilized poly(2-vinylpyridine) (P2VP) latex in dil. Soln.) and also the spontaneous redistribution of silica that occurs when such P2VP-silica nanocomposite particles are challenged by the addn. Of sterically stabilized P2VP latex. Silica adsorption is complete within a few seconds at 20 °C and the rate of adsorption strongly dependent on the extent of silica surface coverage. Similar very short time scales for silica redistribution are consistent with facile silica exchange occurring as a result of rapid interparticle collisions due to Brownian motion; this interpretation is consistent with a zeroth-order Smoluchowski-type calcn. Of excess sterically stabilized P2VP latex to a colloidal dispersion of P2VP-silica nanocomposite particles (with silica shells at full monolayer coverage) leads to the facile redistribution of the silica nanoparticles such that partial coverage of all the P2VP latex particles is achieved. This silica exchange, which is complete within 1 h at 20 °C as judged by small-angle x-ray scattering, is obsd.

For nanocomposite particles prepd. By heteroflocculation, but not for nanocomposite particles prepd.

By in situ copolymn. These observations are expected to have important implications for the optimization of nanocomposite formulations in the coatings industry. SDS wormlike micelles in water with NaBr are studied using small-angle neutron scattering. Ranging from 0.08 to 8.6% vol in NaBr aq. At salinities from 0.6 to 1.0 M are covered. The scattering data are analyzed using a novel approach based on polymer theory and the results of Monte Carlo simulations. The method makes it possible to give a full interpretation of the scattering data, even for the entangled micellar solns.

Occurring at high concns. And high salinities. Of the scattering data at zero scattering angle demonstrates that the length of the micelles increases according to a power law as a function of concn. In the studied interval. Furthermore shows that the length of the micelles increases exponentially with increasing salinity.

The scattering data in the full range of scattering angles are analyzed using a model for polydisperse wormlike micelles where excluded vol. Effects are taken into account via an expression based on the polymer ref. Interaction site model (PRISM). This part of the anal.

Show that the micelles become more flexible as the salinity increases, which is due to an increased screening of the ionic micelles. The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface has previously been calcd. By Pedersen and Gerstenberg. Non-penetration of the chains into the core region was mimicked in the anal. By moving the center of mass of the chains Rg away from the surface of the core, where Rg is the radius of gyration of the chains. In the present work, the calcns.

Have been extended to micelles with ellipsoidal and cylindrical cores. Non-penetration was also for these taken into account by moving the center of mass of the chains Rg away from the core surface. Results for worm-like micelles, disk-shape micelles and micelles with a vesicle shape are given. Off-lattice Monte Carlo simulations on semiflexible polymer chains with and without excluded vol. Interactions have been performed.

The model used in the simulations is a discrete representation of the worm-like chain model of Kratky and Porod applied in the pseudocontinuous limit. The ratio between the cross-section radius R of the chain and the statistical segment length b was chosen to be R/b = 0.1 which corresponds to the value found for polymer-like micelles. The ratio R/b is equiv. To a reduced binary cluster integral of B = 0.30, which is in accordance with the value for polystyrene in a good solvent. The scattering functions of the semiflexible chains have been detd. With a precision of 1-2% for L/b = 0.3-640, where L is the contour length of the chain. Numerical approxns.

To these functions have been detd. Which interpolate between the simulated functions, and these can be used in the anal. Scattering data. The approxns. Have been used in least-squares fitting of exptl.

Small-angle neutron scattering data from polystyrene in a good solvent. Using a newly prepd., nearly monodisperse, (Mw/Mn. Dihydrophilic AB block copolymers of Me vinyl ether (MVE) and Me triethylene glycol vinyl ether (MTEGVE) were prepd. By living cationic polymn., with copolymer mol. In the range 1500-13,900 with fairly narrow mol.

Distributions (Mw/Mn. Zwitterionic shell-crosslinked [SCK] micelles were prepd. As nanoparticles with hydrophilic micelle cores, from 2-(dimethylamino)ethyl methacrylate-2-tetrahydropyranyl methacrylate (DMAEMA-THPMA) diblock copolymer precursors and bis-2-(iodoethoxy)ethane crosslinker. The linear copolymers are readily converted into zwitterionic 2-(dimethylamino)ethyl methacrylate-methacrylic acid (DMAEMA-MAA) blocks by acid hydrolysis. Depending on the reaction conditions used, two classes of zwitterionic SCK micelles can be obtained: type I micelles, which have anionic cores and cationic coronas obtained via quaternization and type II micelles, which have cationic cores and anionic coronas obtained via esterification.

At a certain crit. PH (the iep) the micelles become elec.

Neutral and are pptd. Of acid or base leads to complete redissoln. Of the micelles. This pptn.-dissoln.

Behavior is well-known for conventional proteins and their synthetic analogs but had not been reported for micelles. Diblock copolymers with one block sol. And the other block insol. Were dispersed in an industrial base oil (BO) to yield spherical micelles (SMs).

SMs were also prepd. In more manageable solvents that had similar soly. Properties as the BO towards the copolymers but had lower viscosities and lower b.ps. And absorbed less in the near UV region. The photocrosslinking of the cores of the latter micelles yielded crosslinked micelles or nanospheres.

We have tested the lubrication properties of the micelle and nanosphere samples in BO under conditions simulating those found in automobile engines. Of micelles and nanospheres with 2-cinnamoyloxyethyl acrylate units in their cores exhibited a unique friction redn. Pattern and had friction coeffs. That were significantly lower in the boundary lubrication regime (BLR) than in the mixed lubrication regime. Such particles reduced the friction of the BO by >70% in the BLR and performed substantially better than the widely used industrial anti-friction agent glyceryl monooleate.

The factors affecting this unique friction redn. Behavior were investigated and a possible reason for it was proposed.

Motion Blur: If set to Yes, this option enables, a form of effect most noticeable when you change your view rapidly; the resulting slight blur in the image may improve visual quality and realism for some people, while others may find it distracting. A comparison is provided above however this is a difficult effect to capture in screenshots.

Note that enabling Motion Blur does reduce FPS slightly, but ultimately you should decide whether to use it or not based more on how you feel about its visual impact, and bear in mind that it can also help cover up the shimmering from jagged edges in the game. Wait for Vertical Sync: Vertical Synchronization (VSync) is the synchronization of your graphics card and monitor's abilities to redraw an image on the screen a number of times each second, measured in Hz.

It is explained more clearly on of the Gamer's Graphics & Display Settings Guide. When VSync is enabled (set to Yes), your maximum FPS will be capped at your monitor's maximum refresh rate at your chosen resolution, and more importantly in some areas your FPS may drop by as much as 50% or more if the graphics card has to wait to display a whole frame. Thus enabling VSync can have a major negative performance impact, and the easiest solution is to leave it disabled. However if you find the image 'tearing' annoying, you can enable VSync and counter the subsequent performance drop by also enabling Triple Buffering - see for details of how to enable it properly. Importantly, the game engine has an FPS cap regardless of whether VSync is disabled or not - by default, the game is capped to a maximum of 62 FPS. This is done by the developers to prevent FPS spikes and thus provide smoother performance, and in general it works quite well, especially since Mass Effect is not a fast-paced shooter.

However if you want to remove or alter this FPS cap, see the bSmoothFrameRate, MinSmoothedFrameRate and MaxSmoothedFrameRate variables in the Advanced Tweaking section. Film Grain: If set to Yes, this option enables a mild grainy overlay.

To see an animated screenshot comparison which highlights the impact of the effect, click this link: (317KB). When On, there is a dark grain on the image, most noticeable when contrasted against a lighter background. Film Grain also has tiny swirling motion when viewed on screen, and has a noticeable negative performance impact when enabled. In the end however whether you enable it or not is up to your tastes, as despite the reduction in FPS, it also serves to cover up jaggedness and can make the game much more atmospheric for some people, while others find it annoying. Sound Hardware Audio: If ticked, the game will use hardware acceleration which can improve audio quality and performance. I recommend ticking this option in most circumstances, unless you experience audio glitches or other issues.

Note in particular that you will need to tick this option if you have a multi-channel audio system and want to use more than 2 channels. Vista users with Creative sound cards in particular should enable this option, as it allows for proper hardware acceleration without the need for. However there are many users experiencing problems with getting full multi-channel hardware surround sound in Mass Effect.

First of all, make absolutely certain that your sound card's control panel as well as the Sound properties in the Windows Control Panel are set up correctly to use the number of channels you wish. The game uses Creative's proprietary ISACT OpenAL-based audio system, and this cannot be changed, but there are some issues with the way the game can incorrectly identify audio device capabilities, so if you are still having problems and want proper hardware audio, follow these steps: 1. Go to your (My) Documents BioWare Mass Effect Config directory and rename the BIOEngine.ini file to something else.

Launch Mass Effect without running the Config utility. The game will recreate BIOEngine.ini using default values, and should correctly identify your audio hardware. In the in-game settings Hardware Audio should already be selected - do not change it back to software audio or make any other changes to the Sound settings. If the above steps don't work, follow the additional instructions as described under the [ISACTAudio.ISACTAudioDevice] part of the Advanced Tweaking section of this guide. To see if your sound hardware is being detected properly at any time, exit Mass Effect and open the MassEffect.log file found under your (My) Documents BioWare Mass Effect Logs directory with a text editor. Look for the line starting with Init: Audio Device - it should say 'Generic Hardware' or the name of your audio device.

The lines above it and below it should also have the correct information, and no audio initialization errors should be showing. Obviously, as also noted under the Troubleshooting Tips section of this guide, you must ensure that you are running the latest version of the game, as well as the latest drivers for your audio device.

You can also try installing the latest version of OpenAL for Windows, available. Creative sound card owners in particular may find the latest drivers might resolve their issues if nothing else does.

Dialog, Sound Effects, Music Volume: These sliders control the volume level for spoken dialog, the various sound effects, and the background music in the game respectively. Set them to suit your preference, as they have no performance impact. Input Invert Y Axis: If set to Yes, pushing your mouse forward will make your character look down, and pulling your mouse back will make him look up. Set to suit your taste, has no impact on performance. Hardware Mouse: When ticked this option uses your graphics card hardware to optimize rendering of the mouse cursor, which should give the best performance and smoothness. With Hardware Mouse enabled, the cursor switches from the standard white Windows mouse arrow to a custom blue outlined graphical arrow.

If your cursor disappears when you select this option, restart the game and it should be fixed. If you experience problems with your game crashing during loadup or any mouse-related issues, untick this option. Mouse Sensitivity: This slider controls how sensitive the mouse will be to your movements.

The higher the value, the greater your view movements will be in the game when you move the mouse. If you're experiencing 'mouse lag', that is a feeling of reduced sensitivity or sluggishness in your mouse, regardless of how high you set the mouse sensitivity slider, you should first make sure you are consistently getting sufficient FPS, especially in more complex scenes with lots of effects. Use or the Stat FPS console command (see the Advanced Tweaking section) to check your FPS, and keep in mind that typically anything below 15-20 FPS can bring about mouse lag in most any game, so you will have to lower your settings appropriately to prevent this as much as possible. Next, try disabling VSync as not only is it know to cause mouse lag, it also reduces performance which can make mouse lag even worse. Controls Here you can adjust all the various keyboard and mouse controls. Note that if you wish to customize these further for any reason, see the Advanced Tweaking section.

Gameplay Combat Difficulty: In general the enemies in Mass Effect scale upwards to match the player's level. However the available options here can increase or decrease combat difficulty. The initial options are Casual, Normal, and Veteran - each has successively harder enemies, with more protection/immunity.

There are two additional difficulty levels called Hardcore and Insanity: you can access Hardcore only after you have completed the game on Normal or Veteran difficulty; you can access Insanity difficulty only after you've completed the game on Hardcore difficulty. Note that changing the difficulty at any time during gameplay can negate proper completion of that difficulty level and relevant achievements, so leave difficulty unchanged for the duration of the game.

Auto Level-Up: This option has an important impact on the RPG aspects of Mass Effect. It determines what happens when your character or any members of your squad gain a level. When set to Off, whenever any squad member gains a level you must manually go into the Squad menu and allocate talent points to various skills for each of the characters in your squad; when set to Squad Only, squad members will automatically level up, and you only have to manually allocate your own character's talent points; when set to Squad and Player, the computer automatically allocates talent points to everyone each time they gain a level, without any user input - this is generally not recommended as it prevents you from customizing your character to suit your individual needs.

Target Assist: This setting controls the degree to which the game assists you when aiming at a target. The available options are Low, Normal and High - the higher the setting, the greater your accuracy when aiming. This setting can affect the overall difficulty of combat in the game, so adjust it in combination with the Combat Difficulty setting above to get the desired effect. Squad Power Usage: This setting has an important impact on combat strategy. It determines the way in which members of your squad use any powers they have. If set to Disabled, they will not use any powers unless manually assigned by you; if set to Defence Only they will automatically use defensive powers if necessary; and if set to Active they will use both defensive and offensive powers as they see fit. In general it is recommended that you select 'Defence Only', as this allows them to use defensive powers if they're in danger, but prevents them from wasting their offensive powers at inopportune moments.

Subtitles: If set to Yes, text subtitles are shown for spoken dialog. If set to No, subtitles are not shown at first, however in most cases if you wait long enough at a dialog prompt the last piece of dialog will still be shown as subtitled text. Note that if you want to change the color of the subtitles, see the m_colSubtitleColor setting in the Advanced Tweaking section. Auto Save: If set to Yes, the game will automatically save your progress to a single 'Auto Save' slot at key intervals. This can be useful in case you forget to manually save on a regular basis, however if you don't like the small pauses when the game goes to auto save, then you can set this option to No.

Obviously you must then make sure to save regularly, both using the Save option and also the Quick Save (F6) feature, though note that neither of those options overwrite an Auto Save slot if it exists. Tutorials Enable Tutorials: This option controls the various tutorial messages which appear throughout the game. You should leave this enabled at first when you begin playing, as the advice can be very helpful.

However after the first few hours of gameplay you should be familiar with all the main controls and commands, and thus can disable this option. The next section looks at the Advanced Tweaking possible in Mass Effect.