Influence Of Solvent Quality Research Articles

Influence of solvent quality on the swelling and shear modulus of polymer gels chemically cross-linked in solution

The effect of temperature (T) is studied on the swelling of model poly(vinyl acetate) (PVAc) gels in isopropyl alcohol. The theta temperature Θ of these gels, at which the second osmotic virial coefficient A2 vanishes, is close to that of the corresponding high molecular mass polymer solution without cross-links so that solvent quality may be defined in the same way as the corresponding precursor polymer solution. We quantified the swelling and deswelling of PVAc gels relative to their size at the theta temperature, and also determined the effect of T on the shear modulus of these gels. It was found that both swelling and deswelling data could be reduced to a universal scaling equation of the same general form as derived from renormalization group (RG) theory for flexible linear polymer chains in solutions.Graphical abstractVariaton of the volumetric swelling factor as a function of the reduced temperature for PVAc gels swollen in isopropyl alcohol.

Solvent quality shape control in continuous flow block copolymer self-assembly

The influence of solvent quality on block copolymer self assembly is studied in detail using SANS online monitoring.

Influence of solvent quality on the swelling and deswelling and the shear modulus of semi-dilute solution cross-linked poly(vinyl acetate) gels.

We systematically examine the influence of varying temperature (T) over a large range in model poly(vinyl acetate) gels swollen in isopropyl alcohol. The theta temperature Θ, at which the second virial coefficient A2 vanishes, is found to be equal to within numerical uncertainty to the corresponding high molecular mass polymer solution value without cross-links, and we quantify the swelling and deswelling of our model gels relative to their size at T = Θ, as customary for individual flexible polymer chains in solutions. We also quantify the "solvent quality" dependence of the shear modulus G relative to G(T = Θ) and compare to the hydrogel swelling factor, α. We find that all our network swelling and deswelling data can be reduced to a scaling equation of the same general form as derived from renormalization group theory for flexible linear polymer chains in solutions so that it is not necessary to invoke either the Flory-Huggins mean field theory or the Flory-Rehner hypothesis that the elastic and mixing contributions to the free energy of network swelling are separable to describe our data. We also find that changes of G relative to G(T = Θ) are directly related to α. At the same time, we find that classical rubber elasticity theory describes many aspects of these semi-dilute solution cross-linked networks, regardless of the solvent quality, although the prefactor clearly reflects the existence of network defects whose concentration depends on the initial polymer concentration of the polymer solution from which the networks were synthesized.

Impact of the Solvent Quality on the Local Dynamics of Soft and Swollen Polymer Nanoparticles Functionalized with Polymer Chains.

Grafting polymer chains on the surface of nanoparticles (NPs) is a strategy used to control the interaction between the NPs and their environment. The fate of the resulting particles in a given environment is strongly influenced by the solvent–polymer interaction. The solvent quality affects the behavior, conformation, and dynamics of the grafted polymer chains. However, when this polymer grafting strategy is used to functionalized polymer particles, the influence of solvent quality becomes even more complex; when the grafted polymer chains and the polymer nanoparticles are tethered together, the effect of the solvent quality on the behavior and dynamics of the system depends on the solvent interaction with both polymer components. To explore the relationship between the solvent quality and the dynamics of polymer-functionalized soft polymer NPs, we designed a system based on cross-linked polystyrene (PS) NPs grafted with a canopy of poly(methyl acrylate) (PMA). PS and PMA, two immiscible polymers, can be selectively solvated by using binary mixtures of solvents. NMR spectroscopy was used to address the effect of those selective solvents on the local mobility of the PS–PMA core-canopy NPs and revealed an interplay between the local mobility of the core and the local mobility of the canopy. A selective reduction of the solvent quality for the PMA canopy resulted in the expected reduction of the local mobility of the PMA chains, but also in the slower dynamics of the PS core. Similarly, a selective reduction of the solvent quality for the PS core resulted in a slower dynamics for both the PS core and the PMA canopy.

Influence of Solvent Quality and Crystallization Conditions on the Drawability of Ultra-High Molecular Weight Polyethylene Cast from Solution

The standard route toward high-performance polyethylene fibers involves “ultra-drawing”: large-strain solid-state uniaxial plastic deformation at elevated temperatures of precursor ultra-high molec...

Influence of Solvent Quality on the Force Response of Individual Poly(styrene) Polymer Chains.

Single molecule mechanics of poly(styrene) polymer chains is investigated in different organic solvents with atomic force microscopy (AFM). The acquired force-extension profiles can be well fitted with a modified freely jointed chain (FJC) model. The model describes the force-extension profiles in terms of an apparent Kuhn length and an elasticity constant. The elasticity constant is found to be the same for all different solvents investigated. Best fit of the force-extension profiles with the FJC model reveals that the Kuhn length varies systematically with solvent quality. In fact, one can establish a good correlation between the Kuhn length and the Flory-Huggins interaction parameter. The increase in the Kuhn length with increasing solvent quality reflects the larger extent of swelling of the polymer in good solvents.

From melt to solution: Scaling relations for concentrated polystyrene solutions

The scaling relations established for the relaxation modulus of concentrated solutions of polystyrene (PS) in oligomeric styrene [Wagner, Rheol. Acta 53, 765–777 (2014); Wagner, J Non-Newtonian Fluid Mech. (2015)] are applied to the solutions of PS in diethyl phthalate (DEP) investigated by Bhattacharjee et al. [Macromolecules 35, 10131–10148 (2002)] and Acharya et al. [AIP Conf. Proc. 1027, 391–393 (2008)]. The scaling relies on the difference ΔTg between the glass-transition temperatures of the melt and the glass-transition temperatures of the solutions. ΔTg can be inferred from the reported zero-shear viscosities, and the Baumgaertel, Schausberger, and Winter (BSW) spectra of the solutions are obtained from the BSW spectrum of the reference melt with good accuracy. Predictions of the extended interchain pressure (EIP) model, which is based on the assumption that the relative interchain pressure in the melt and in the solutions is identical, are compared to the steady-state elongational viscosity data of PS/DEP solutions. The Rouse stretch relaxation times as calculated from the respective scaling relation are a factor of 2–3 higher than the Rouse time defined by the experimentally observed upturn of the elongational viscosity at WiR=ε̇ τR→1. This may be caused by DEP being a good solvent at room temperature and/or polymer degradation. Using the experimentally determined Rouse times, quantitative agreement is obtained between experimental data and model. Except for a possible influence of solvent quality, linear and nonlinear viscoelasticity of entangled PS solutions can thus be obtained from the linear-viscoelastic characteristics of a reference polymer melt and the shift of the glass-transition temperature between melt and solution.

Influence of solvent quality on successive solution fractionation (SSF) efficiency of high‐density polyethylene

AbstractBACKGROUND: Preparative successive solution fractionation (SSF) is a powerful technique for obtaining narrow‐dispersity fractions on a multi‐gram scale of high‐density polyethylene (HDPE). In a previous paper, the operative separation mechanisms during SSF of a broad HDPE in cyclohexanone were studied. Two mechanisms, and not only one as expected from the literature, contribute to the separation of HDPE molecules according to their molar mass (MM). The very low MM chains are separated by a solid–liquid (S–L) mechanism, while the longer chains are isolated by a liquid–liquid (L–L) phase separation. In the present paper, the influence of a poorer solvent, diphenyl ether, is reported.RESULTS: It is shown that the relative importance of the S–L mechanism with respect to the L–L one is altered by the use of this solvent. The L–L temperature range is increased in diphenyl ether while the S–L transition temperature remains unchanged. Consequently, the SSF efficiency is improved. Large amounts (on a gram scale) of narrow‐dispersity fractions are isolated, mainly by the L–L mechanism. Polydispersities are about 1.5 (compared to 2.0 for cyclohexanone) and a broader MM range of closer molar mass distribution fractions is available.CONCLUSION: This work demonstrates that the use of diphenyl ether, a poorer solvent than cyclohexanone (always used as SSF solvent for polyethylene in the literature), leads to an improvement of SSF efficiency for an essentially linear HDPE. The differences of behaviour during the separation with cyclohexanone or diphenyl ether are explained by the establishment of a phase diagram. Copyright © 2009 Society of Chemical Industry

The Soret effect in dilute polymer solutions: Influence of chain length, chain stiffness, and solvent quality

Thermal diffusion in dilute polymer solutions is studied by reverse nonequilibrium molecular dynamics. The polymers are represented by a generic bead-spring model. The influence of the solvent quality on the Soret coefficient is investigated. At constant temperature and monomer fraction, a better solvent quality causes a higher affinity for the polymer to the cold region. This may even go to thermal-diffusion-induced phase separation. The sign of the Soret coefficient changes in a symmetric nonideal binary Lennard-Jones solution when the solvent quality switches from good to poor. The known independence of the thermal diffusion coefficients of the molecular weight is reproduced for three groups of polymers with different chain stiffnesses. The thermal diffusion coefficients reach constant values at chain lengths of around two to three times the persistence length. Moreover, rigid polymers have higher Soret coefficients and thermal diffusion coefficients than more flexible polymers.

Influence of Solvent Quality on the Self-Organization of Archetypical Hairy Rods−Branched and Linear Side Chain Polyfluorenes: Rodlike Chains versus “Beta-Sheets” in Solution

We report on the nanoscale structure and solvent-induced phase behavior of two, nearly similar π-conjugated hairy-rod polymers, branched side chain poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6) and linear side chain poly[9,9-dioctylfluorene-2,7-diyl] (PFO or PF8), in good and bad (or poor) solventsdeuterated toluene and deuterated methylcyclohexane (MCH)at 20 °C. Small-angle neutron scattering (SANS) measurements exploiting contrast variation with side chain deuterated PFO polyfluorene have been employed and complemented by optical absorption measurements. In toluene both PF2/6 and PFO adopt an elongated (rodlike) conformation containing predominantly only a single polymer chain (diameter of the order of 1 nm), which indicates dissolution down to the molecular level. In contrast, in MCH, PF2/6 shows an elongated structure while PFO forms sheetlike structures (characteristic thickness of 2−3 nm), thus dissolving down to the “colloidal” level. The elongated structure of PFO consists of individual polymer chains adopting dominantly a conformational isomer Cα. The thickness of sheetlike PFO particles corresponds to that of around two polymer layers and side chain contrast variation gives an evidence for an even distribution of the backbones within the sheets. These sheets are potentially an initial stage of PFO crystallization and also contain conformational isomer Cβ of those chains observed in the so-called beta-phase (or beta-sheets) in the solid state. The observed phenomena were not found to depend on concentration over the concentration range 5−10 mg/mL.

Mechanical properties of poly(vinyl methyl ether) hydrogels below and above their volume phase transition

The mechanical properties of radiation cross-linked poly(vinyl methyl ether) hydrogels below and above the volume phase transition (VPT) under isobar conditions were studied. The viscoelastic properties as a function of radiation dose, radiation source and polymer concentration at the state of irradiation were examined. Increased radiation doses led to higher cross-linking densities and higher moduli. Hydrogels irradiated with γ-rays were much harder than those obtained with electron beam irradiation at the same radiation dose. It was found that the modulus strongly increased by up to 1 order of magnitude at a temperature of the VPT of about 37 °C. In the collapsed state at temperatures well above the VPT a frequency dependence of the E′(ω) moduli in the range 0.1–22 Hz was detected, indicating viscoelastic behavior. To study the influence of solvent quality on the modulus of the hydrogels, rheological measurements were performed in water, 2-propanol and cyclohexane. A scaling exponent for the modulus according to de Gennes (G′∝φ2.25) was not found. Possible reasons for deviations (G′∝φ3.54) on poly(vinyl methyl ether) hydrogels were discussed in the context of deviations from ideal networks.

Influence of solvent quality on polymer solutions: a Monte Carlo study of bulk and interfacial properties.

The effect of solvent quality on dilute and semidilute regimes of polymers in solution is studied by means of Monte Carlo simulations. The equation of state, adsorption near a hard wall, wall-polymer surface tension, and effective depletion potential are all calculated as a function of concentration and solvent quality. We find important differences between polymers in good and theta solvents. In the dilute regime, the physical properties for polymers in a theta solvent closely resemble those of ideal polymers. In the semidilute regime, however, significant differences are found.

Conformational Aspects and Intramolecular Phase Separation of Alternating Copolymacromonomers: A Computer Simulation Study

AbstractSummary: Using the bond fluctuation model (BFM), simulations have been performed on molecular bottle brushes with two chemically different types of side chains. In the first part of this work, rigidity of the backbone is imposed. The influence of solvent quality and side chain length on the intramolecular phase separation of side chain material, leading to Janus cylinders, has been investigated and compared to theoretical predictions. In the second part of this work, the restriction of rigidity for the backbone is relaxed. In a poor solvent, the side chain material collapses into a globular state. Several globules containing each one type of side chain material are connected together by backbone material. When imposing different solvent conditions for both types of side chains, a bending of the backbone is found as predicted by theory and observed in very recent experiments.Comparison between typical snapshots in θ solvent. The side chain length is 25 beads. Dark and light coloured side chains repel each other.imageComparison between typical snapshots in θ solvent. The side chain length is 25 beads. Dark and light coloured side chains repel each other.

Influence of Solvent Quality on the Growth of Polyelectrolyte Multilayers

The effect of solvent conditions on the growth of polyelectrolyte (PE) multilayer films comprising poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) on planar substrates was investigated by means of surface plasmon resonance spectroscopy (SPRS), quartz crystal microbalance (QCM), and atomic force microscopy techniques. The solvent quality was varied by the addition of ethanol to the PE solutions used for deposition of the layers, thus tuning the relative strength of electrostatic and secondary intermolecular and intramolecular interactions. Experiments were performed with PE solutions both without added electrolyte and containing 0.5 M NaCl. Decreasing the solvent quality (i.e., increasing the amount of ethanol in the adsorption solution) resulted in a marked increase of both the multilayer film thickness and mass loading, as determined from the SPRS spectra and QCM frequency shifts, respectively. With the solution composition approaching the precipitation point, thick PAH/PSS films were formed due to the screening of the electrostatic intra- and interchain repulsions and enhanced hydrophobic interactions between the polyelectrolyte chains. However, the films formed from water/ethanol mixtures remained stable upon subsequent exposure to water or salt-containing solutions: no significant film desorption occurred after up to 24 h of exposure to water or 0.5 M NaCl solutions. In addition, the effect of postdeposition exposure to water/ethanol mixtures was investigated for PE multilayers assembled from aqueous solutions. In this case, the optical thickness of the films was determined during exposure to water/ethanol mixtures, and instead of swelling, the polyelectrolyte films collapse to the surface as a result of the unfavorable segment-solvent interactions.

Equilibrium Swelling and Universal Ratios in Dilute Polymer Solutions: Exact Brownian Dynamics Simulations for a Delta Function Excluded Volume Potential

A narrow Gaussian excluded volume potential, which tends to a delta-function repulsive potential in the limit of a width parameter d* going to zero, has been used to examine the universal consequences of excluded volume interactions on the equilibrium and linear viscoelastic properties of dilute polymer solutions. Brownian dynamics simulations data, acquired for chains of finite length, has been extrapolated to the limit of infinite chain length to obtain model independent predictions. The success of the method in predicting well known aspects of static solution properties suggests that it can be used as a systematic means by which the influence of solvent quality on both equilibrium and non-equilibrium properties can be studied.

Influence of solvent quality on effective pair potentials between polymers in solution.

Solutions of interacting linear polymers are mapped onto a system of "soft" spherical particles interacting via an effective pair potential. This coarse-graining reduces the individual monomer-level description to a problem involving only the center of mass (c.m.) of the polymer coils. The effective pair potentials are derived by inverting the c.m. pair distribution function, generated in Monte Carlo simulations, using the hypernetted chain closure. The method, previously devised for the self-avoiding walk model of polymers in good solvent, is extended to the case of polymers in solvents of variable quality by adding a finite nearest-neighbor monomer-monomer attraction to the previous model and varying the temperature. The resulting effective pair potential is found to depend strongly on temperature and polymer concentration. At low concentration the effective interaction becomes increasingly attractive as the temperature decreases, eventually violating thermodynamic stability criteria. However, as polymer concentration is increased at fixed temperature, the effective interaction reverts to mostly repulsive behavior. These issues help to illustrate some fundamental difficulties encountered when coarse-graining complex systems via effective pair potentials.

The influence of solvent quality on the mechanical properties of thin cast isotactic poly(methyl methacrylate) coatings

Thin coatings of isotactic poly(methyl methacrylate) were cast on glass from solvents of different quality, which was expected to result in different molecular morphologies. The elastic moduli and hardness of the coatings were measured using a nanoindenter. The aim was to examine the viability of this technique for assessing the influence of the morphology on the mechanical properties. The interpretation of the data was complicated by both the influence of the hard substrate and possibly by the plasticising effect of retained solvent in the bulk. Nevertheless, it was reasonable to conclude that a coating cast from a good solvent was stiffer and harder than that from a poor solvent. This is consistent with previous frictional and spectroscopic studies.

Viscous and elastic properties of a cationic and a zwitterionic drag reducing surfactant

The cationic CTAC and zwitterionic SPE 98330 surfactants were investigated and their rheological properties compared. Also the influence of solvent quality (the presence of ions, particularly Ca 2+) on both the viscosity and elasticity of surfactants were investigated. Differences in the storage modulus, G′, are negligible but there are substantial differences in the loss modulus, G′′. Shear induced state (SIS) was detected in all samples.

Influence of Solvent Quality and Thermal Fluctuations on Polymer-Mediated Depletion Interactions

Analytic integral equation theory for treating athermal mixtures of hard spheres and polymers is extended to study thermal interaction and solvent quality effects in suspensions of infinitely dilute spherical particles in dilute and semidilute polymer solutions. Our approach applies to all sphere/polymer size ratios, and polymer−polymer segmental attractive interactions are included using both liquid state and Flory−Huggins theory. The effect of such thermal interactions on the polymer-induced depletion potential between hard spheres is studied with emphasis on the sphere−sphere second virial coefficient and the free energy of particle insertion. Strong enhancement of the purely entropic attractive depletion interaction is found in the proximity of the polymer−solvent critical demixing point. The magnitude of this effect and the distance from the ϑ temperature where it becomes important are sensitive to system-specific factors.

Reversible gels of synthetic polymers: Phase relations, formation mechanisms and structure

AbstractThe complex problem of thermoreversible gelation of solutions of synthetic polymers is discussed. Several possible mechanisms, based on supramolecular structure formation in solution, are discussed. The gelation of polyethylene solutions illustrates the structure formation through lamellar, folded chain crystallization. Gelation of solutions of stereoisomers of polystyrene and poly(methyl methacrylate) is more complex and two mechanisms can are proposed. The complex temperature‐concentration phase diagrams of syndiotactic polystyrene/solvent systems illustrate the competition between gelation by crystallization and the formation of elastic gels. The influence of chain conformation, participation of the solvent in the structure formation and the influence of solvent quality is discussed. Insight in the formation mechanism of elastic gels is obtained through the study of the gelation of solutions of syndiotactic poly(methyl methacrylate).