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Size exclusion chromatography is the method of choice for the molar mass analysis of polymers, however, it is not selective towards polymer microstructure. Counterintuitively, asymmetric flow field-flow fractionation (AF4), a channel-based molar mass analysis technique, has been shown to be able to fractionate poly(methyl methacrylate (PMMA) according to tacticity. This was revealed by investigating the solution behaviour of syndiotactic- (s-PMMA), atactic- (a-PMMA) and isotactic (i-PMMA) poly(methyl methacrylate) of similar molecular masses in solvents with different thermodynamic properties. In addition to developing a selective fractionation method, the effects of solvent quality and channel temperature on the fractionation were investigated. It was concluded that the thermodynamic quality of the carrier liquid has a significant influence on the retention behaviour of polymers in AF4. It was shown that the separation of s-PMMA and i-PMMA can be improved by using a theta solvent (acetonitrile) as the carrier liquid instead of thermodynamically good solvents such as tetrahydrofuran and chloroform. In addition, it was found that by using a non-stereocomplexing solvent for PMMA, such as chloroform, blends of s-PMMA and i-PMMA can be separated. Lastly, it was established that the AF4 channel temperature has an influence on the retention behaviour of the PMMA samples. For THF as carrier liquid it was found that the maximum difference in retention between s-PMMA and i-PMMA can be achieved at a channel temperature of 35 °C. In the case of ACN being the carrier liquid, it was observed that the retention behaviour of i-PMMA was significantly more influenced by a change in temperature as compared to s-PMMA and a-PMMA.

Hypothesis: Previous works have shown that many-body interactions induced by dispersants with increasing correlation length will generate a diminishing two-phase region [Soft Matter 14, 6921 (2018)]. We conjecture that the attenuation of the depletion attraction due to many-body interactions is a ubiquitous phenomenon in medium-induced interactions. We propose mixtures of colloidal particles and rod-like polymers as a feasible experimental system for verifying these predictions, since the intra-molecular correlations are not screened in a good solvent for rod-like polymers as they are in flexible polymers. The length of the rods can grow and become the dominant length scale that determines the range of the depletion interactions for the imbedded non-adsorbing particles. Simulations: We study many-body depletion forces induced by polymerizing rod-like polymers on spherical non-adsorbing colloids, using Metropolis Monte Carlo simulations. We also employ a simple mean-field theory to further justify our numerical predictions. Findings: We demonstrate that the phase diagram displays the same qualitative features that have previously been predicted by many-body theory, for mixtures containing flexible polymers under theta solvent conditions. The contraction of the particle two-phase region that we observe, as the correlation length increases beyond some specific value, could be a signature of the weakening of the depletion caused by many-body effects.

Decagram scale syntheses of deuterated mineral oil (d-MO) and poly(1-decene) (d-PD) were achieved by direct catalytic hydrothermal H/D exchange reaction in D2O. Nuclear magnetic resonance (NMR), mass density and small angle neutron scattering (SANS) analyses collectively revealed deuteration ratios of 54 ± 12% and 88 ± 4% for d-MO and d-PD, respectively. Further SANS analyses of polyethylene (PE) dissolved in d-MO revealed that the oil behaved as a theta solvent at temperatures of 100 and 120 °C, based on assessments of the radii of gyration and mass-fractal dimensions in the PE coils. These results suggest that PE chains in d-MO likely adopt the same coiled molecular conformations as those reported for PE in the molten state. This approach of deuterating the oil solvent, in lieu of the polymer analyte, may have far reaching applications for the SANS assessments of oil additives in polymer materials. Additionally, such deuterated oils are expected to exhibit improved stability and oxidative resistance, which will benefit many applications given the ubiquitous use of mineral oil in industry.

We examined the packing structure of polystyrene-coated gold nanoparticles (Au@PS) as a function of grafting density. A series of Au@PS nanoparticles with grafting densities in the range of 0.51–1.94 chains nm–2 were prepared by a ligand exchange process using thiol-terminated PS and then self-assembled at a liquid–air interface. We observed a transition from disordered to body-centered cubic (bcc) to face-centered cubic (fcc) arrangements with increasing grafting density, even though the ligand length-to-core radius ratio (λ) was as high as 3.0, a condition that typically favors nonclose-packed bcc symmetry in the self-assembly of hard nanoparticles. To explain this phenomenon, we define λeff to include the concentrated polymer brush regime as part of the “hard core”, which predicts that the softness of Au@PS nanoparticles is reduced from 1.53 to 0.14 in a theta solvent as the grafting density increases from 0.51 to 1.94 chains nm–2. This new definition of λ can also predict the effective radii of nanopa...

Rubber tires undergo viscoelastic losses at high and low frequencies. High frequency losses lead to traction while low frequency losses lead to rolling resistance. High rolling resistance tires require greater amount of fuel to travel a particular distance as compared to low rolling resistance tires, and thus they have a negative impact on vehicle fuel economy. Traction is needed for vehicle braking ability and propulsion. Maintaining a balance between reducing rolling resistance and maintaining wear resistance and traction is a technical challenge. Factors that decrease rolling resistance tend to worsen traction, and vice versa, while both types of changes reduce wear resistance. Experiments have found that strengthening interactions between rubber and reinforcement fillers can be used to maintain a balance between reducing tire rolling resistance without compromising on wear resistance and traction, but why this works is not known. Rolling resistance on the macroscale connects directly to energy losses occuring due to changes in elastomer chain conformations on the microscale. Thus, understanding the statistical mechanics of elastomer chain conformations provide us a vital molecular link towards quantifying rolling resistance. This thesis provides a first step towards this link. Molecular modeling is used to study the size and shape distribution, and characteristics of cisand trans-1,4-polybutadiene chains. Computations are conducted using Flory’s Rotational Isomeric State approach (RIS), in which energy distribution is considered over discrete rotational isomeric states. The Rotational Isomeric State approach is chosen because it allows generating a large number of polybutadiene chains in a computationally cheap manner using less resources and computation time , and also because the RIS approach allows each chain realization to be treated as an independent sample. Numerous (100,000) isolated single cisand trans-1,4-polybutadiene chains of uncorrelated random conformations are considered under unperturbed conditions (balanced attractive and repulsive polymer-solvent interactions, i.e. thetaconditions). Using a single chain in each computation is justified because a flexible polymer surrounded by the same polymer takes on the same average shape as a single random polymer chain in a theta solvent. Chain size and shape properties are computed at different chain lengths and over a range of temperatures. Characteristic ratios are in good agreement with experimental and prior computed values (cis-1,4-polybutadiene), and slightly higher than prior computed values (trans-1,4-polybutadiene). Characteristic ratios increased with increasing chain length for both cis and trans chains with this effect being more prominent for trans than for cis chains. Small absolute changes in chain size probability densities with temperature are observed. Larger relative increase in probability density of larger chains and smaller relative decrease in probability density of smaller chains result in increased average chain size with increasing temperature. This effect increases characteristic ratios with increasing temperature. The larger chains show a much higher increase in characteristic ratios with temperature than smaller chains, and this effect is stronger for trans than for cis chains. Eigenvalues of the radius of gyration matrix quantify chain shapes by providing eigenvalues along the three principal directions (eigenvectors). Average shape measures differ between cis and trans chains. With increasing chain length, trans chains are slightly compressed along the principal direction while cis chains are slightly stretched. Resultantly, trans chains are slightly more spherical with increasing chain length while cis chains are slightly less spherical. At the same chain length, trans chains are slightly less spherical than cis chains. At long chain lengths, trans and cis chains have similar spherical shapes. With increasing temperature, little or no variation in shape is computed for cis chains, whereas trans chains are slightly stretched along the principal direction, and thus are slightly less spherical. Most changes in shapes arise from changes along the longest principal direction. Cis and trans chains show similar asphericity (a parameter that quantifies deviation from spherical shape) at longer chain lengths. Little or no change in acylindricity (a parameter that quantifies deviation from cylindrical shape) is computed for either cis or trans polybutadiene chains. Relative shape anisotropy (a shape parameter) follows the same trends like asphericity as functions of both chain length and temperature for cis and trans polybutadiene chains. Joint correlation studies reveal that size and shape parameters are mutually dependent properties of chains. For asphericity, rod-like small size and spherical medium size cis chains show anti-correlation between chain size and shape. Spherical small size, near rod-like medium and large size chains show correlation between chain size and shape. For acylindricity, medium size chains of flattened cross section, and small and large size chains of round cross section showed correlation between chain size and shape. Round cross section medium size chains show anti-correlation between chain size and shape. Trans chains show similar behavior as cis chains with correlation and anti-correlation between chain size and shape occuring to a greater extent. The next use for the detailed conformation results in this work is to relate probability densities to the work done to alter chain size and shape. Cis and trans chains show different probability density distributions implying different amounts of deformation work to alter chain size and shape. When a tire revolves and deflects while in motion, affine deformation of the elastomer-filler system takes place. The deformation leads to changes in elastomer chain conformations, which results in entropy losses of the elastomer-filler system (since entropy is related logarithmically to chain conformations). These entropy losses lead to computing irreversible work, viscoelastic losses and rolling resistance. The effects of fillers on these conformation distributions thus will quantify interaction effects on loss modulus and rolling resistance.

We present a new system of bi-component hydrogels formed of l -lysine hydrochloride mixed with sodium tetraphenyl borate with unusual viscoelastic properties which might be useful in tissue engineering, nano-particles synthesis or bioseparation. Beside cationic-anionic molecular interactions, 1H-NMR experiments have also shown the presence of π-electrons cloud interactions as well as hydrogen bonds stabilizing the supramolecular structure. Bulk rheological and mechanical properties have been characterized using steady and oscillatory shear rheometry as well as uniaxial compression tests. Microstructural information has been deduced from multi particle tracking (MPT) optical microrheology and cryo-preparation scanning electron microscopy (SEM). These gels are shear thickening at low concentrations and shear thinning at higher gelator concentration. Shear and Young’s modulus data obtained from different techniques agree fairly well. Zero shear viscosity as well as modulus data obtained for gels with equimolar lysine and borate concentration exhibit concentration dependence η 0 ∼ c 5 ± 0.5 and G 0 ∼ c 3.4 ± 0.35 , respectively. The scaling exponent for η 0 agrees well with predictions for neutral polymer in theta solvent or wormlike micelles in the slow breaking regime whereas the variation in G 0 is unexpectedly high. We attribute this to the unique microstructure consisting of a cellular structure composed of thin sheets connected by tiny fibers. At low concentrations the mesh size of this structure is about 10 μm and fiber diameter increases from ∼200 nm to ∼2 μm, only at the highest gelator concentration of 7 wt.% the mesh size shrinks to ∼5 μm and the fiber diameter to ∼400 nm. Consistently, tracer particles in low concentrated gels diffuse freely in an aqueous environment. At higher gelator concentration, however, gelation takes place so fast that tracers are trapped in the elastic sheets / fibrous regions and the modulus G M P T ´ agrees fairly well with bulk data. Varying the molar ratio of both gel-forming components results in a pronounced viscosity maximum at fixed total gelator concentration. Corresponding microstructural changes could again be visualized using cryo-SEM consistent with MPT data. At high lysine fraction, a coarse coral reef type sheet structure is found while at low lysine to borate ratio a network of thick struts is formed. Finally, diffusing wave spectroscopy experiments performed on samples with different lysine to borate ratio revealed that the plateau modulus G0 is almost independent of temperature whereas the relaxation time TR becomes faster as temperature increases.

Rheological properties of water-soluble dietary fibre (DF), including yellow mustard mucilage (YMM), soluble flaxseed gum (SFG), fenugreek gum (FG) and oat gum (OG) were studied following a simulated gastric and small intestinal digestion. Experimentally obtained steady shear flow curves of FG, SFG and OG were fitted to the Cross model. Based on the values of the Huggins constant, small intestinal fluid at 37 °C is a good solvent for SFG and FG and a theta solvent for OG. The degree of space occupancy at critical overlap concentration ( c *[η]) for OG and FG were lower than expected from “normal” concentration-dependency. This departure was attributed to intermolecular associations of these DF in simulated small intestinal conditions. Apparent viscosities (at 60 s −1 ) of simulated small intestinal digesta containing oat β-glucan at concentrations expected in the small intestine after consumption of a meal that meets from 0.5 to 3 times the value of the European Food Safety Authority (2011) health claim on reduction of post-prandial glycemic responses were determined and were used as benchmarks. Concentrations of YMM, SFG and FG that resulted in apparent viscosities close to the benchmark apparent viscosities in simulated small intestinal conditions were found. In the majority of cases, these concentrations were different for each DF.

Preferential solvation of polymer chains by molecules of the thermodynamically better component of the solvent mixture is a general phenomenon which affects properties of dissolved chains a...

“Mobile” polymer brushes with self-adjustable tethering density can be found in the single crystals of amorphous-crystalline diblock copolymers in the thermodynamically stable state. In such a system, the amorphous blocks form polymer brushes on the surface of the single crystal of the crystalline blocks. Different from the common polymer brushes with fixed tethering density, of which polymers are attached either chemically or physically on a substrate, the polymer brushes tethered on the single crystal are “smart” and partially release the highly stretched conformation by “telling” the crystalline blocks to provide more surface area via forming higher folded chain single crystals. Such a polymer brushes system is treated theoretically using the Flory approximation. Thicknesses of the amorphous polymer brush layer (La) and the single crystal lamellae (Lc) are found to have different scaling relations with the degree of polymerization of the amorphous block (ra) in different types of solvents. The amorphous layer thickness, La, is proportional to the 2/3 power of ra in a poor solvent for the amorphous blocks, the 3/4 power in theta solvent, and the 4/5 power in good solvent. The scaled powers between La and ra of the “mobile” polymer brushes are all weaker than the normal polymer brushes, which scales with ra to the first power, indicating the partial releasing of the stretched nature. The crystal thickness, Lc, is proportional to the −1/3 power of ra in poor solvent for the amorphous blocks, the −1/2 power in theta solvent, and the −3/5 power in good solvent, clearly indicating that a folded chain single crystal possesses a larger number of folds at a large ra to facilitate the crowding of the amorphous chains on the surface.

To optimize the performance of polymer solar cells, various techniques have been developed and reported from various research fields. The introduction of processing additives in the polymer : PCBM bulk-heterojunction solution is one of the efficient strategies used to improve the cell performance. Although numerous solvents have been presented as processing additives, an appropriate processing additive is always different for each polymer solar cell. In this manuscript, we demonstrate that diphenyl ether (DPE) works as a widely beneficial processing additive, which provides high-performance polymer solar cells from all types of photovoltaic polymers. DPE acts like a theta solvent to photovoltaic polymers, helps to form ideal bulk-heterojunction film morphologies and suppresses bimolecular charge recombination. This study suggests an efficient way to optimize the performance of polymer solar cells using DPE regardless of the photovoltaic polymers used.

We predict morphology-controlled nanopumping of a nonselective solvent in the swollen lamellae-forming diblock copolymer systems under applied uniaxial deformation of the sample. Normal compression of the lamellae at conditions that the solvent is not extruded (evaporated) from the sample (so-called “sealed” sample) leads to the solvent flow from the lamellar interior to the AB interfaces. On the contrary, the normal expansion results in the increase of the solvent concentration at the interfaces which is practically not accompanied by the solvent flow from the interfaces to the lamellar interior. The physical reason for the nanopumping is shown to be related to the shielding of unfavorable AB contacts of the monomer units at the interface via localization of the solvent molecules. As a result, the solvent concentration at the interface is larger than within the lamellae. Interplay between variation of the interfacial area under the deformation and minimization of their tension is responsible for the solv...

Molecular characteristics of an atactic polystyrene (aPS) chain with different lengths in a theta solvent, cyclohexane at 307.65 K, were studied via molecular dynamics (MD) simulation. The interaction energy of the aPS dilute solution models and Flory–Huggins (FH) interaction parameter were calculated to investigate the effect of the chain molecular weight on its compatibility with the solvent molecules. The simulation results illustrated that increasing the chain length increased the interactions between the chain and the solvent molecules. The chain dimensions via calculating the radius of gyration (Rg) and end-to-end distance, , were measured. Mean square displacement (MSD) and diffusivity coefficient of the chains were calculated to determine their dynamic behavior. The results exhibited that two factors of the chain movability and size were important for the diffusion in oligomeric state. Additionally, viscosity of the resultant dilute solutions was calculated via nonequilibrium molecular dynamics simulation (NEMD). Moreover, the steric hindrance of the chains was determined by radial distribution function (RDF) analysis. The calculated characteristics of the chain and solution viscosity results showed a good agreement with experimental published works. Measurement of the potential field of cyclohexane–cyclohexane and aPS–cyclohexane pairs was also based on their potential field via quantum chemical calculations to determine the special orientation of the solvent molecules to each other and to the polymer segments, respectively.

Analytical temperature rising elution fractionation (TREF) of linear polyethylene (PE) samples with different densities was done in 1-chloronaphthalene using a gel permeation chromatograph (GPC) coupled with a gas chromatograph. The corrected peak elution temperatures completed the previously obtained data in trichlorobenzene, xylene, and dibutoxymethane. A mathematical correlation was found for diluted linear PE samples between the α parameter of the Mark-Houwink-Sakurada equation governing the retention time in GPC, the bulk melting temperature measured by differential scanning calorimetry (DSC), and the TREF peak elution temperature. The extrapolation to the melting temperature measured by DSC gives α = 0.5, thus confirming the hypothesis that polymer conformations in the melt are similar to those in a theta solvent.

The conformation of 38 kDa PEO in a solvate ionic liquid (SIL), lithium tetraglyme bis(trifluoromethane-sulfonyl)amide ([Li(G4)]TFSI) from dilute to concentrated solution regimes has been determined by small angle neutron scattering and rheology. SANS analysis reveals that [Li(G4)]TFSI is better than a theta solvent (theta-good) for PEO. The variation of the radius of gyration (Rg) and viscosity as a function of polymer concentration allow the overlap concentrations, c* and c**, to be identified at 13 mg mL(-1) and 50 mg mL(-1), respectively, which are similar to values reported previously for conventional ionic liquids. Unlike water and conventional ionic liquids, [Li(G4)]TFSI cannot form hydrogen bonds with PEO. Thermal gravimetric analysis indicates that the solvation of PEO by [Li(G4)]TFSI is a consequence of PEO forming coordinate bonds with the lithium by displacing the anion, but without displacing the glyme molecule.

In thin and ultrathin supported films, the conformations of flexible linear polymer chains might be considerably confined, in particular, for film thicknesses smaller than a few times the radius of gyration. For ring polymers in solution or in melt, the radii of gyration are significantly reduced as compared to those of their linear counterparts. We study here the influence of geometrical confinement on the chain conformation of cyclic PNIPAM in silicon-supported films. Measurements are performed by grazing incidence small angle neutron scattering (GISANS). For all films, the component of the radius of gyration parallel to the substrate, Rgc∥, is significantly higher than the unperturbed Rgc determined under theta solvent or melt conditions. We attribute this effect to a preferential selection of stretched PNIPAM ring conformations in thin films and a preferential orientation of macromolecules parallel to the film interfaces with the substrate and air.

Polysaccharides, such as cellulose, are often processed by dissolution in solvent mixtures, e.g. an ionic liquid (IL) combined with a dipolar aprotic co-solvent (CS) that the polymer does not dissolve in. A multi-walker, discrete-time, discrete-space 1-dimensional random walk can be applied to model solvation of a polymer in a multi-component solvent mixture. The number of IL pairs in a solvent mixture and the number of solvent shells formable, x, is associated with n, the model time-step, and N, the number of random walkers. The mean number of distinct sites visited is proportional to the amount of polymer soluble in a solution. By also fitting a polynomial regression model to the data, we can associate the random walk terms with chemical interactions between components and probe where the system deviates from a 1-D random walk. The ‘frustration’ between solvents shells is given as ln x in the random walk model and as a negative IL:IL interaction term in the regression model. This frustration appears in regime II of the random walk model (high volume fractions of IL) where walkers interfere with each other, and the system tends to its limiting behaviour. In the low concentration regime, (regime I) the solvent shells do not interact, and the system depends only on IL and CS terms. In both models (and both regimes), the system is almost entirely controlled by the volume available to solvation shells, and thus is a counting/space-filling problem, where the molar volume of the CS is important. Small deviations are observed when there is an IL–CS interaction. The use of two models, built on separate approaches, confirm these findings, demonstrating that this is a real effect and offering a route to identifying such systems. Specifically, the majority of CSs – such as dimethylformide – follow the random walk model, whilst 1-methylimidazole, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone and tetramethylurea offer a CS-mediated improvement and propylene carbonate results in a CS-mediated hindrance. It is shown here that systems, which are very complex at a molecular level, may, nonetheless, be effectively modelled as a simple random walk in phase-space. The 1-D random walk model allows prediction of the ability of solvent mixtures to dissolve cellulose based on only two dissolution measurements (one in neat IL) and molar volume.

We investigate conformations and effective interactions of polymer-coated nanopar- ticles adsorbed at a model liquid-liquid interface via molecular dynamics simulations. The polymer shells strongly deform at the interface, with the shape governed by a balance between maximising the decrease in interfacial area between the two solvent components, minimising unfavourable contact between polymer and solvent and max- imising the conformational entropy of the polymers. Using potential of mean force calculations we compute the effective interaction between the nanoparticles at the liquid-liquid interface. We find that it differs quantitatively from the bulk and is sig- nificantly affected by the length of the polymer chains and by the solvent quality. Under good solvent conditions the effective interactions are always repulsive and soft for long chains. The repulsion range decreases as the solvent quality decreases. In particular, under poor solvent conditions, short chains may fail to induce steric repul- sion, leading to a net attraction between the nanoparticles, whereas with long enough chains the effective interaction potential may feature an additional repulsive shoulder at intermediate distances.

Well-defined block copolymers of poly(ethylene glycol)-block-polystyrene (PEG-b-PS) were synthesized by atom transfer radical polymerization with predetermined molecular weights and narrow molecular weight distributions (1.06–1.08). The single crystals of PEG-b-PS copolymers were grown in chlorobenzene/octane mixed theta solvent using self-seeding technique. The effect of self-seeding temperature (T s) on single crystal lateral size was evaluated. The atomic force microscopy (AFM) height images were indicative of increasing the single crystal lateral sizes, which were of several microns, via elevating T s. The non-ideal structures were increasing by moving away from the optimized T s (41.5 °C). Here, we studied the transition point between non-interaction and interaction regimes in a mixed theta solvent for PS as well. The impact of the PS block hindrance and the influence of crystallization temperature on thickness, tethering density and reduced tethering density of PS brushes were also investigated. Although these factors did not have the same effect on thickness and tethering density, the trend of their influence on reduced tethering density was the same. The results were recognized by AFM, transmission electron microscopy and small angle X-ray scattering.

Light-scattering measurements were carried out on polyisoprene (PI) samples with weight-averaged molecular weights (Mws) ranging from 1.1 × 103 to 2.7 × 104 in 1,4-dioxane at and near the theta point, 35.3 °C, which is defined as the temperature at which the second virial coefficient A2 for sufficiently high Mw (larger than 1 × 104) vanishes. It was found that A2 at the theta point decreases with decreasing Mw for Mw

Both Hansen solubility parameter and Flory–Huggins interaction parameter of two EVA [Poly(ethylene-co-vinyl acetate)] copolymers with different vinyl acetate content have been obtained by means of intrinsic viscosity measurements. To calculate this last parameter it was also necessary to determine the theta solvent at different temperatures of the two EVA copolymers with turbidimetric measurements. The results indicate that the vinyl acetate content is a variable which influences the composition of the theta solvent and Flory–Huggins parameter (the higher the vinyl acetate content, the lower the Flory–Huggins parameter), although its influence over the Hansen solubility parameter is almost negligible.

Etude par SANS de PE lineaires et en etoile en solution dans le biphenyle-d10 et le toluene-d8 et comparaison avec les resultats obtenus precedemment a l'etat fondu. Pour le solvant theta, les valeurs du facteur d'expansion obtenues pour les polymeres en etoile sont interpretables par une theorie a 3 parametres; pour l'autre solvant, les valeurs obtenues sont en accord avec les modeles a 2 parametres traditionnels

The influence of both polymer chain length and concentration on the mobility of solvent molecules in polymer solutions was studied by Monte Carlo simulations with the use of the dynamic lattice liquid (DLL) model. The poly(vinylmethylether)-water system was used as a model. Two different solvent (water) states with differing mobilities were distinguished in polymer solutions. The first one with high molecular mobility independent of polymer concentration corresponds to bulk solvent in real systems. The second state relates to so called bound solvent. In this case the solvent diffusivity decreases with polymer content. For diluted solutions the diffusion of bound solvent is affected by polymer chain length, precisely, by the ability of the polymer chain to undergo coil formation.

A novel experimental method for the analysis of volume relaxation induced by solvents in glassy polymers is presented. A gravimetric technique is used to evaluate the isothermal solvent mass uptake at controlled increasing/decreasing solvent pressure at constant rate. Fundamental properties of the solvent/polymer system can be obtained directly, and models can be applied, combining both nonequilibrium thermodynamics and mechanics of volume relaxation contribution. The fundamental case of polystyrene and toluene mixtures are thus accounted for, and various experimental conditions have been explored, varying the temperature, and spanning over different pressure increase/decrease rates. The results obtained allowed to evaluate the isothermal second order transition induced by solvent sorption, as well as the determination of the effect of the pressure rate. Therefore, this work proposes a new standard for the characterization and the understanding of the relaxational behavior of glassy polymers.

Based on the Wilemski-Fixman approach G. Wilemski, M. Fixman, J. Chem. Phys. 60 (1974) 866], we show that, for a flexible chain in theta solvent, hydrodynamic interaction treated with a pre-averaging approximation makes ring closing faster if the chain is not very short. We also show that the ring closing time for a long chain with hydrodynamic interaction in theta solvent scales with the chain length (N) as N-1.5, in agreement with the previous renormalization group calculation based prediction by Freidman and O'Shaughnessy B. Friedman, B. O'Shaughnessy, Phys. Rev. A 40 (1989) 5950]. (C) 2012 Elsevier B.V. All rights reserved.

In the present study, transport mechanisms of various binary systems such as alcohol–hexane, alkane–hexane, lipid–hexane, and diesel fuel–kerosene systems through a PDMS-based dense membrane were investigated using a combined regular solution (RS) and solution-diffusion (SD) model at constant pressure and temperature. The combined model contains many important factors for permeability such as diffusivity, degree of swelling membrane, membrane thickness, and osmotic pressure. Total, hexane, and solvent fluxes (except for a part of the solvent flux) of all systems were controlled by molar volumes of hexane and solvent and solubility parameters of hexane, solvent, and membrane polymer based on the combined model. The selectivity of the solvent in these systems seems to depend upon the similarity of the molecular structures of hexane and solvent, corresponding to entropy mixing, and the interaction of the hexane–solvent–membrane polymer, corresponding to enthalpy mixing. The combined model could well describe the transport mechanism of the binary system.

We study the effect of film preparation on the equilibration and viscoelastic properties of polymer films. Polystyrene films with a thickness of 14 nm are spun-cast from decalin solutions at different temperatures near the theta temperature to produce films with different chain conformations. We find that the equilibration time of the films increases significantly near the theta temperature. We attribute this to the onset of a rapid collapse in the polymer coil size at the theta condition, along with an increase in the solvent concentration in the films and thereby interchain separation at the time of vitrification. We find that these effects also cause the plateau modulus and equilibrium viscosity of the films to decrease.

Dissipative particle dynamics (DPD) is used to investigate solvent flow controlled by a cylindrical nanofluidic channel grafted with polymer brushes. Results for monomer and solvent beads density for different solvent quality were obtained, as well as the height and inclination angle of the polymer brushes in Poiseuille flow. The velocity profile and solvent permeability in Poiseuille flow for varying solvent quality were also examined. The polymer brushes expand and inhibit flow under good solvent conditions. However, under poor solvent conditions the chains collapse to open the channel. Additionally, the dependence of the permeability on the grafting density is given. The results indicate that the system is capable of changing the permeability and flow rate drastically upon changing the solvent quality.

Soft polymeric gels have utility in a broad range of medical, industrial, and military applications, which has led to an extensive research investment over the past several decades. While most gel research exploits a cross-linked polymer network swollen with small molecule solvents, this article systematically investigates the impact of the solvent molecular weight on the resulting gel mechanical properties. The model polymer gel was composed of a chemically cross-linked polydimethylsiloxane (PDMS) network loaded with a non-reactive PDMS solvent. In addition to investigating the impact of solvent loading, the solvent molecular weight was varied from 423,000 g/mol to 1250 g/mol, broadly spanning the molecular weight of entanglement for PDMS (MW ENT ∼29,000 g/mol). The gels exhibited a strong frequency dependent mechanical response when the solvent molecular weight >MW ENT . In addition, scaling factors of shear storage modulus versus solvent loading displayed a distinct decrease from the theoretical value for networks formed in a theta solvent of 2.3 with increasing measurement frequency and solvent molecular weight. The frequency dependent shear storage modulus could be shifted by the ratio of solvent molecular weights to the 3.4 power to form a master curve at a particular solvent loading indicating that mobility of entangled solvent plays a critical role for the mechanical response. In addition, the incorporation of entangled solvent can increase the toughness of the PDMS gels.

A nylon 6 sample having average molecular mass 4.825 × 105 g mol−1 was fractionated into five different fractions with respect to molecular mass, which ranged from 3691 to 999,000 g mol−1. The light scattering and intrinsic viscosity measurements were made in m-cresol and its mixture with 1,4-dioxane. The second virial coefficient, radius of gyration and Mark Houwink's constant and unperturbed chain dimensions were determined by light scattering and viscosity measurement. It has been observed that all these parameters are composition of solvent and temperature dependent. The solvent having composition of 97% m-cresol and 3% dioxane, was best and it deteriorated with the increase/decrease in percentage of 1,4-dioxane in m-cresol. However, its thermodynamic quality was enhanced with the temperature. Such variation in quality of solvent was reflected in all the estimated parameters and showed maxima at this composition of solvent. The unperturbed dimensions obtained by different methods though, differed in values but showed same trend and NA-MKB method gave close results to the one obtained through [ηo]. A new expression has also been proposed relating ko to solvent quality and temperature and the data obtained by us for nylon-6 and the one obtained from the literature for dextran obeyed this expression up to large extent irrespective of the solvent composition and temperature. The proposed equations have also been applied to dextran/methoxy ethylene and dextran/ethylene glycol systems and worked well. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

The structural properties of a polymer-containing ionic liquid under the conditions of good solubility of a flexible polymer are studied theoretically. Two systems are discussed: In one, polymer solubility is due to the presence of specific interaction between polymer chains and solvent cations; in the other, polymer solubility is due to the presence of specific interactions between the polymer and solvent anions. The dependences of the structural characteristics of a solution on the polymer concentration and the energy of attraction between polymer chains and solvent ions are calculated. In a semidilute polymer solution, long-range correlations of polymer chains with a power dependence of the characteristic scale of ordering on the polymer density appear. The conditions under which, along with the intermediate ordering typical of a pure ionic liquid, the long-range ordering of the solvent cations and anions occur after addition of a polymer to the ionic liquid are studied.

We propose an efficient method for investigating conformational properties of a polymer in solvent. The method is a combination of a Monte Carlo (MC) simulation applied to the polymer alone and a statistical-thermodynamic approach for incorporating solvent effects. To illustrate it, we analyze conformations of a simple polymer chain stabilized in a hard-sphere solvent. The generation of polymer conformations is performed using the self-avoiding random walk on a cubic lattice. We argue that by introducing the generalized-ensemble techniques to the MC simulation part, the method can be applied to studies on protein conformations in aqueous solution under any thermodynamic condition.

In this work, we investigated the behavior of poly(dimethylsiloxane-co-diphenylsiloxane)s under good and theta solvent conditions by using turbidimetry and viscosimetry. The evolution of the optical properties as a function of the solvent quality allowed the composition of the methylbenzene/methanol mixtures at the theta point to be determined. The intrinsic viscosity was determined in good (methylbenzene) and theta (methylbenzene/methanol) solvents at T = 298 K using different approaches. The unperturbed dimension parameters were calculated and are discussed as a function of copolymer composition. The introduction of the diphenylsiloxane units into a poly(dimethylsiloxane) chain results in an increase in the unperturbed dimensions as a consequence of the decrease in chain flexibility.

We have performed dissipative particle dynamics (DPDs) simulations of electroosmotic flow (EOF) through a polymer-grafted nanopore. In this model, charged particles including salt ions and counterions are not included explicitly, and EOF is created using an effective boundary condition. The screening effect of polymer layer on EOF is investigated in detail under different solvent qualities and boundary electroosmotic velocities. Results show that the solvent quality has a significant effect on the conformational properties of polymer chains and the flow characteristics of the solvent. The polymer layer undergoes a collapsed transition when decreasing the solvent quality from good to poor. Under different solvent qualities, enhancing the EOF leads to a different variation tendency of the layer thickness. The solvent-induced permeability change is inconsistent with the steady velocity away from the surface. The minimum value of the solvent permeability occurs at an intermediate solvent quality. However, the layer thickness drops gradually to a smallest value (corresponding to the largest effective pore radius) in the poor solvent condition. It is also found that the polymer inclination and stretching length exhibit a complex behavior under the combined effect of solvent quality and electroosmosis-induced shear.

Internal motions of narrowly poly(N-isopropylacrylamide) (PNIPAM) linear chains and spherical microgels in a very dilute aqueous solution and dispersion were studied under the Θ and poor solvent co...

In this work we investigate the effect of the solvent quality on the thermodynamic behavior of the polydimethyldiphenylsiloxane copolymer by using turbidimetry and viscosimetry. The turbidimetric method was used for the determination of the composition of the solvent mixture at the theta point. The experimental data obtained by using the capillary viscometry both in good and theta solvent conditions have been processed by using classical Huggins equation and new Wolf model (2007), which allows the calculation of intrinsic viscosities and other hydrodynamic parameters. The results obtained by using the two approaches were discussed comparatively. The conformational properties of copolymer in solution depend on their molecular structure, which is essentially dominated by the solvent quality, reflecting the balance of the interactions between the polymer chains and each solvent and that between solvent molecules.

Shielding effects of the surrounding arms and the chain on the encounter probability of reactive sites taking part in the Z-RAFT star polymerization are investigated (a) by use of lattice based Monte Carlo simulations in combination with exact enumeration techniques and (b) by direct simulation applying an off-lattice coarse-grained molecular dynamics method (dissipative particle dynamics, DPD). Making use of the former method the chain-length dependence of the shielding factors is discussed for a broad range of thermodynamic conditions and compared to DPD results for the athermal (good solvent) and theta (bad solvent) case, i.e., for the limiting solvent qualities evaluated. In addition, changes of the size and shape of the reaction partners on approach and penetration are discussed in some detail. The results of both simulation methods fairly well coincide and reveal that shielding is smaller and chain-length dependence less pronounced under theta conditions as compared to good solvent conditions. Experimentally determined polydispersities of polystyrene generated by Z-RAFT star polymerizations in the poor solvent cyclohexane were found to be smaller than with the good solvent toluene, which is in full accordance to the theoretical predictions.

In this work, we use the vapor-sorption equilibrium data to show the degree of solvent upturn in each solvent-polymer system. For this purpose, 20 isothermal data sets for five polymer + solvent binaries have been used in the temperature range of 298–413 K. Solvents studied are benzene, pentane, hexane, toluene, and chlorobenzene. Homopolymers studied are: polystyrene, poly(vinyl acetate), polyisobutylene, and polyethylene. According to these data sets, solvent weight fraction in the polymer is plotted against solvent vapor activity that is calculated assuming an ideal gas phase of pure solvent vapor neglecting the vapor pressure of the polymer. We use the Flory-Huggins theory to obtain dimensionless interaction parameter, χ. Also the Zimm-Lundberg clustering theory and non-ideality thermodynamic factor, Γ are used to interpret the equilibrium data. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010