Polymer-solvent Interaction Parameter Research Articles

Quantitative Macromolecular Modeling Assay of Biopolymer-Based Hydrogels.

The rubber elasticity theory has been lengthily applied to several polymeric hydrogel substances and upgraded from idealistic models to consider imperfections in the polymer network. The theory relies solely on hyperelastic material models in order to provide a description of the elastic polymer network. While this is also applicable to polymer gels, such hydrogels are rather characterized by their water content and visco-elastic mechanical properties. In this work, we applied rubber elasticity constitutive models through hyperelastic parameter identification of hydrogels based on their stress-strain response to compression. We further performed swelling experiments and determined the intrinsic properties, i.e., density, of the specimens and their components. Additionally, we estimated their equilibrium swelling and employed it in the swelling-equilibrium theory in order to determine the polymer-solvent interaction parameter of each hydrogel with regard to cross-linking. Our results show that the average mesh size obtained from the rubber elasticity theory can be regarded as a concentration-dependent characteristic length of the hydrogel's network and couples the non-linear elastic response to the specimens' inherent visco-elasticity through hysteresis as a quantifier of energy dissipation under large deformation.

Revealing the Kinetic Phase Behavior of Block Copolymer Complexes Using Solvent Vapor Absorption-Desorption Isotherms.

Controlling the self-assembled morphologies in block copolymers heavily depends on their molecular architecture and processing conditions. Solvent vapor annealing is a versatile processive pathway to obtain highly periodic self-assemblies from high chi (χ) block copolymers (BCPs) and supramolecular BCP complexes. Despite the importance of navigating the energy landscape, controlled solvent vapor annealing (SVA) has not been investigated in BCP complexes, partly due to its intricate multicomponent nature. We introduce characteristic absorption-desorption solvent vapor isotherms as an effective way to understand swelling behavior and follow the morphological evolution of the polystyrene-block-poly(4-vinylpyridine) block copolymer complexed with pentadecylphenol (PS-b-P4VP(PDP)). Using the sorption isotherms, we identify the glass transition points, polymer-solvent interaction parameters, and bulk modulus. These parameters indicate that complexation completely screens the polymer interchain interactions. Furthermore, we established that the sorption isotherm of the homopolymer blocks serves to deconvolute the intricacy of BCP complexes. We applied our findings by developing annealing pathways for grain coarsening while preventing macroscopic film dewetting under SVA. Here, grain coarsening obeyed a power law and the growth exponent revealed a kinetic transition point for rapid self-assembly. Overall, SVA-based sorption isotherms have emerged as a critical method for understanding and developing annealing pathways for BCP complexes.

Solid-Liquid-Solution Phases in Poly(diallyldimethylammonium)/Poly(acrylic acid) Polyelectrolyte Complexes at Varying Temperatures.

The coacervation and complexation of oppositely charged polyelectrolytes are dependent on numerous environmental and preparatory factors, but temperature is often overlooked. Temperature effects remain unclear because the temperature dependence of both the dielectric constant and polymer-solvent interaction parameter can yield lower and/or upper critical solution phase behaviors for PECs. Further, secondary interactions, such as hydrogen bonding, can affect the temperature response of a PEC. That is, mixtures of oppositely charged polyelectrolytes can exhibit phase separation upon lowering and/or increasing the mixture's temperature. Here, the phase behavior of poly(diallylmethylammonium)/poly(acrylic acid) (PDADMA/PAA) complexes under varying KBr ionic strengths, mixing ratios, and temperatures at a fixed pH (in which PAA hydrogen bonding can occur) is examined. At room temperature, the PDADMA/PAA PECs exhibit four different phase states: precipitate, coexisting precipitate and coacervate, solid-like gel, and coacervate. Variable-temperature optical microscopy reveals the upper critical solution temperature (UCST) at which each phase transitioned to a solution state. Interestingly, the UCST value is highly dependent on the original phase of the PEC, in which solid-like precipitates exhibit higher UCST values. Large-scale all-atom molecular dynamics (MD) simulations support that precipitates exhibit kinetic trapping, which may contribute to the higher UCST values observed in the experiment. Taken together, this study highlights the significance of temperature on the phase behavior of PECs, which may play a larger role in stimuli-responsive materials, membraneless organelles, and separations applications.

The Transient Response of the Swelling in Mixed Solvent for the Freeze/Thawed Polyacrylonitrile Gel Observed in Association with the Polymer Elution

The swelling properties of polyacrylonitrile gel prepared by the repeating cycle of freezing and thawing were examined, as its transient response toward the equilibrium swollen states varies with the variation of mixing ratio (r) of the immersion solvent which consisted of N, N–dimethylacetamide and benzene. Two experimental protocols were used; successive solvent exchanges were conducted in Protocol 1, and no solvent exchange but the varying of the volume of immersion solvent was conducted in Protocol 2. Also, the aging time was set between the end of the freezing and thawing cycle and the start of the swelling experiment. As a result, the equilibrium swelling ratio decreased with the increase in the aging time. Significant discrepancies for the transient responses were found for the immersion solvents between r ≤ 0.74 and r ≥ 0.78 both in Protocol 1 and 2, in which the elution of polyacrylonitrile molecules was related to the responses. A characteristic overshoot curve was observed in the swelling with r ≥ 0.78 in Protocol 2, which was also attributed to the polyacrylonitrile elution. The polymer solvent interaction parameter was calculated on the basis of the osmotic pressure equilibrium, which was associated with the interpretation of the transient response data.

Sustained Release of Drug Facilitated Through Chemically Crosslinked Polyvinyl Alcohol-Gelatin (PVA-GE) Hydrogels. A sustainable biomedical approach

Abstract The present study aimed to prepare hydrogel based on polyvinyl alcohol (PVA) and gelatin (Ge) and characterization of PVA/Ge hydrogel for their potential use as a sustained drug delivery system. Polyvinyl Alcohol (PVA) and-Gelatin (Ge) were cross-linked using glutaraldehyde (GA) as a crosslinking agent and hydrochloric acid (HCl) as a catalyst. Different feed polymer ratio and crosslinking agent concentration were used to prepare a series of PVA/Ge hydrogels. The obtained PVA/Ge hydrogels were investigated for dynamic and equilibrium swelling studies. The effect of polymers ratio, degree of crosslinking and pH of the medium on swelling of PVA/Ge hydrogels was investigated. Furthermore, the values of diffusion coefficient (D), volume fraction, polymer-solvent interaction parameter, molecular weight between crosslink and crosslink density were calculated. For swelling studies, 0.05M USP phosphate buffer solutions of different pH (1.2, 5.5, 6.5 and 7.5) were used. For the drug release study, ciprofloxacin HCl was loaded into selected samples as a model drug. The release of drug from these samples was performed for 12 hours in USP phosphate buffers of pH 1.2, 5.5 and 7.5. The release data from these samples were fitted into various kinetic models like zero order, first order, Higuchi and Peppas models to investigate the release mechanism. It was found that by varying the composition of PVA/Ge hydrogel and GA concentration, a significant difference was observed in drug release kinetics. FTIR spectroscopy and X-ray diffraction were used for the characterization of hydrogels. PVA/Ge hydrogel showed sustained release of the model drug at various pH values suggesting its potential use as a sustained drug delivery system.

Comparison of Cyclic and Linear Poly(lactide)s Using Small-Angle Neutron Scattering.

Small-angle neutron scattering (SANS) experiments were conducted on cyclic and linear polymers of racemic and l-lactides (PLA) with the goal of comparing chain configurations, scaling, and effective polymer-solvent interactions of the two topologies in acetone-d 6 and THF-d 8. There are limited reports of SANS results on cyclic polymers due to the lack of substantial development in the field until recently. Now that pure, well-defined cyclic polymers are accessible, unanswered questions about their rheology and physical conformations can be better investigated. Previously reported SANS experiments have used cyclic and linear polystyrene samples; therefore, our work allowed for direct comparison using a contrasting (structurally and sterically) polymer. We compared SANS results of cyclic and linear PLA samples with various microstructures and molecular weights at two different temperatures, allowing for comparison with a wide range of variables. The results followed the trends of previous experiments, but much greater differences in the effective polymer-solvent interaction parameters between cyclic and linear forms of PLA were observed, implying that the small form factor and hydrogen bonding in PLA allowed for much more compact conformations in the cyclic form only. Also, the polymer microstructure was found to influence polymer-solvent interaction parameters substantially. These results illustrate how the difference in polymer-solvent interactions between cyclic and linear polymers can vary greatly depending on the polymer in question and the potential of neutron scattering as a tool for identification and characterization of the cyclic topology.

Investigation of thermodynamic properties of Amine Modified Polystyrene and its use for separation of isomers

In this study, thermodynamic properties, glass transition temperature and isomer separation ability of PVBC (poly (vinyl benzyl chloride)) -Diethanol amine (PVBC-DEA) polymer was investigated by IGC method. For purpose, the retention diagrams were drawn using interactions between PVBC-DEA with selected isomer solvents (i-butyl acetate, n-butyl acetate and t-butyl acetate) at between 85 and 110°C. The glass transition temperature value of the polymer was determined from the retention diagrams as 76°C and the obtained value, it has been understood that this value is compatible with 75.2°C found by differential scanning calorimetry. The selectivity coefficients, ∝, of the isomer solvents were determined for the PVBC-DEA in the infinite dilution, according to the results obtained, it was revealed that the polymer can separate the isomers. The polymer-solvent interaction parameters for Flory-Huggins theory, χ12∞, and the equation of state theory, χ12*,the effective exchange energy parameters, χeff, the weight fraction activity coefficient, Ω1∞, and also the partial molar heat of mixing at infinite dilution of solvent, ΔH¯1∞, the molar heat of vaporization of solvent, ΔH¯v, and the partial molar heat of sorption of solvent, ΔH¯s, were calculated between 85 and 110°C. The obtained results were discussed.

Dynamic model of monovalent-divalent cation exchange in polyelectrolyte gels

A multicomponent model that imposes conservation laws and constitutive relations for polymer chains, water, and ions was investigated by determining the transient changes in a negatively charged gel exposed to a solution containing both mono- and divalent cations. Association of ion exchange with gel volume is achieved by imposing a linear relation between the polymer-solvent interaction parameter and concentration of divalent cations adsorbed onto the polymer chains. Semiquantitative agreement with measurements made on sodium polyacrylate gels is demonstrated in three aspects: (1) dynamics of gel swelling and deswelling, (2) ion partitioning coefficient, and (3) effect of cross-link density. These results imply that the multicomponent coarse-grained continuum modeling approach can be useful for quantitative predictions over macroscopic length and timescales including the description of volume transitions exhibited by these systems.

Re-Entrant Conformation Transition in Hydrogels.

Hydrogels are attractive materials not only for their tremendous applications but also for theoretical studies as they provide macroscopic monitoring of the conformation change of polymer chains. The pioneering theoretical work of Dusek predicting the discontinuous volume phase transition in gels followed by the experimental observation of Tanaka opened up a new area, called smart hydrogels, in the gel science. Many ionic hydrogels exhibit a discontinuous volume phase transition due to the change of the polymer–solvent interaction parameter χ depending on the external stimuli such as temperature, pH, composition of the solvent, etc. The observation of a discontinuous volume phase transition in nonionic hydrogels or organogels is still a challenging task as it requires a polymer–solvent system with a strong polymer concentration dependent χ parameter. Such an observation may open up the use of organogels as smart and hydrophobic soft materials. The re-entrant phenomenon first observed by Tanaka is another characteristic of stimuli responsive hydrogels in which they are frustrated between the swollen and collapsed states in a given solvent mixture. Thus, the hydrogel first collapses and then reswells if an environmental parameter is continuously increased. The re-entrant phenomenon of hydrogels in water–cosolvent mixtures is due to the competitive hydrogen-bonding and hydrophobic interactions leading to flow-in and flow-out of the cosolvent molecules through the hydrogel moving boundary as the composition of the solvent mixture is varied. The experimental results reviewed here show that a re-entrant conformation transition in hydrogels requires a hydrophobically modified hydrophilic network, and a moderate hydrogen-bonding cosolvent having competitive attractions with water and polymer. The re-entrant phenomenon may widen the applications of the hydrogels in mechanochemical transducers, switches, memories, and sensors.

Asymmetric-Flow Field-Flow Fractionation of complex waterborne polymer dispersions: Effect of the concentration of water in the measurement of molar mass distributions

Asymmetric-Flow Field-Flow Fractionation is a very powerful technique for measuring the molar mass distribution of polymers with complex microstructures. The analysis of some samples such as self-crosslinkable latexes requires to directly dissolve the polymer dispersion in the eluent (THF) without drying it, and this work studies the effect of the presence of this water in those analysis. Taking a polystyrene latex as model system, it was observed that the measured molar mass and radius of gyration increased as the concentration of water in the sample increased. This was an effect of a decrease in the compatibility between the solvent mixture (THF and water) and the polymer, which formed aggregates, and could be predicted calculating the polymer-solvent interaction parameter. When the study was extended to poly(methyl methacrylate), poly(n-butyl acrylate) and poly(vinyl acetate) the same general trend was observed, however, the impact of the water was less significant as the hydrophilicity of the polymer increased. Most importantly, if the samples with the highest water content were first dissolved in THF and afterwards dried using MgSO4 the measured molar mass and radius of gyration values were the same as for the reference sample (dried in the oven), providing a method to analyze samples that cannot be dried into a film and remove the negative effect of the water at the same time.

Accounting for Cooperativity in the Thermotropic Volume Phase Transition of Smart Microgels.

A full quantitative description of the swelling of smart microgels is still problematic in many cases. The original approach of Flory and Huggins for the monomer–solvent interaction parameter cannot be applied to some microgels. The reason for this obviously is that the cross-linking enhances the cooperativity of the volume phase transitions, since all meshes of the network are mechanically coupled. This was ignored in previous approaches, arguing with distinct transition temperatures for different meshes to describe the continuous character of the transition of microgels. Here, we adjust the swelling curves of a series of smart microgels using the Flory–Rehner description, where the polymer–solvent interaction parameter is modeled by a Hill-like equation for a cooperative thermotropic transition. This leads to a very good description of all measured microgel swelling curves and yields the physically meaningful Hill parameter . A linear decrease of is found with increasing concentration of the cross-linker N,N-methylenebisacrylamide in the microgel particles p(NIPAM), p(NNPAM), and p(NIPMAM). The linearity suggests that the Hill parameter corresponds to the number of water molecules per network chain that cooperatively leave the chain at the volume phase transition. Driven by entropy, water molecules of the solvate become cooperatively “free” and leave the polymer network.

Effect of Crosslinker Amount on Properties of Poly Phenylacrylamide Gels

The monomer phenyl acrylamide was synthesized by reacting acrylamide with chloro benzene in the presence of pyridine. Fourier transform infrared spectroscopy (FT-IR) was used to characterize the resulting monomer. High conversion poly phenyl acrylamide (PPAM) containing 0, 0.5, 1, 1.5 and 2 wt % (in conversion to mass of PPAA) of N,N'-methylenebisacrylamide (MBAA) as crosslinker have been successfully synthesized. The effect of MBAA percentage on swelling parameters, clarity, mechanical and thermal properties of the prepared xerogels and hydrogels were studied. 1.5 wt % of MBAA is required to obtain clear xerogels and hydrogels. The water content (EWC), volume fraction of polymer (φ2) and weight loss during swelling decrease with increasing MBAA content. Young’s and shear modulus (E and G) increase as MBAA content increases, the values of E and G are 0.661–3.878 MPa and 0.423–2.588 MPa, respectively. The hydrogels were characterized in terms of modulus crosslinking density (ve and vt) and polymer-solvent interaction parameters (χ). The results are 0.252–0.661 mol/dm3 for ve, 0.211–0.541 mol/dm3 for vt, and 0.813–0.987 for χ. Thermal properties of polymers enhance (Tg increase) by adding MBAA. These types of polymers and their hydrogels possess new properties with potential uses in different medical applications.

Sorption Characteristics of Polymer Brushes in Equilibrium with Solvent Vapors.

While polymer brushes in contact with liquids have been researched intensively, the characteristics of brushes in equilibrium with vapors have been largely unexplored, despite their relevance for many applications, including sensors and smart adhesives. Here, we use molecular dynamics simulations to show that solvent and polymer density distributions for brushes exposed to vapors are qualitatively different from those of brushes exposed to liquids. Polymer density profiles for vapor-solvated brushes decay more sharply than for liquid-solvated brushes. Moreover, adsorption layers of enhanced solvent density are formed at the brush–vapor interface. Interestingly and despite all of these effects, we find that solvent sorption in the brush is described rather well with a simple mean-field Flory–Huggins model that incorporates an entropic penalty for stretching of the brush polymers, provided that parameters such as the polymer–solvent interaction parameter, grafting density, and relative vapor pressure are varied individually.

Determination of Binary Interaction Parameters for Ternary Polymer–Polymer–Solvent Systems Using Raman Spectroscopy

AbstractMultilayer coatings and drying of polymer films are widely used to produce different applications like organic electronics or barrier foils. If the product quality requires separated layers, partial or immiscible systems can be used to avoid interdiffusion between the layers. For the prediction of a possible phase separation of a ternary polymer–polymer–solvent system, it is required to measure or obtain from a data bank the three binary interaction parameters of the system to describe its thermodynamic behavior. This poses a challenge due to the scarce data and measurement techniques for polymer–solvent interaction parameters, but even more for polymer–polymer interaction parameters. In this work, a numerical routine is developed to predict the phase separation for given interaction parameters and is validated with literature results. Subsequently, different ternary polystyrene–poly(methyl methacrylate)–toluene mixtures are prepared and the resulting composition of the phase (or phases) is measured via Raman spectroscopy. The determined equilibrium data are used to fit the binary interaction parameters, which can be used afterward as input parameters for the numerical routine in order to predict the ternary phase diagram of the system.

The role of physicochemical properties in the nanoprecipitation of cellulose acetate

The cellulose acetate (CA) nanoparticles (NPs) were prepared via the nanoprecipitation technique. The effects of solvent mixture quality and order of addition on the size evolution of CA NPs were investigated. The size of CA NPs was reduced by decreasing the nonsolvent-solvent mixture interaction parameter (χNS−mS) and by increasing the polymer-solvent mixture interaction parameter (χP−mS). The NPs prepared by the method of addition of the polymer solution to the nonsolvent were smaller than those prepared by addition of the nonsolvent to the polymer solution. The very small CA NPs with the diameter of 37 nm and very narrow PdI of 0.045 were fabricated without using any surfactant and charged groups. The role of surface tension and osmotic pressure forces on the formation of NPs were discussed. The formation mechanism of NPs could be assigned to the rapid polymer precipitation and solidification (vitrification) of the nuclei.

Phase Diagrams of n-Type Low Bandgap Naphthalenediimide-Bithiophene Copolymer Solutions and Blends.

Phase diagrams of n-type low bandgap poly{(N,N′-bis(2-octyldodecyl)naphthalene -1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′,-(2,2′-bithiophene)} (P(NDI2OD-T2)) solutions and blends were constructed. To this end, we employed the Flory–Huggins (FH) lattice theory for qualitatively understanding the phase behavior of P(NDI2OD-T2) solutions as a function of solvent, chlorobenzene, chloroform, and p-xylene. Herein, the polymer–solvent interaction parameter (χ) was obtained from a water contact angle measurement, leading to the solubility parameter. The phase behavior of these P(NDI2OD-T2) solutions showed both liquid–liquid (L–L) and liquid–solid (L–S) phase transitions. However, depending on the solvent, the relative position of the liquid–liquid phase equilibria (LLE) and solid–liquid phase equilibria (SLE) (i.e., two-phase co-existence curves) could be changed drastically, i.e., LLE > SLE, LLE ≈ SLE, and SLE > LLE. Finally, we studied the phase behavior of the polymer–polymer mixture composed of P(NDI2OD-T2) and regioregular poly(3-hexylthiophene-2,5-dyil) (r-reg P3HT), in which the melting transition curve was compared with the theory of melting point depression combined with the FH model. The FH theory describes excellently the melting temperature of the r-reg P3HT/P(NDI2OD-T2) mixture when the entropic contribution to the polymer–polymer interaction parameter (χ = 116.8 K/T − 0.185, dimensionless) was properly accounted for, indicating an increase of entropy by forming a new contact between two different polymer segments. Understanding the phase behavior of the polymer solutions and blends affecting morphologies plays an integral role towards developing polymer optoelectronic devices.

Viscometric behavior of hydroxyethyl cellulose in aqueous solutions of some imidazolium ionic liquids

In this work, viscosity of hydroxyethyl cellulose in aqueous solutions of ionic liquids, 1-butyl-3-methyl imidazolium bromide, 1-hexyl-3-methyl imidazolium bromide and 1-octyl-3-methyl imidazolium bromide were measured at temperature range of T = 288.15–308.15 K. Some hydrodynamic and thermodynamic parameters such as intrinsic viscosity, polymer–solvent interaction parameter and second virial coefficient were calculated using viscosity data. Obtained results reveal that thermodynamic quality of aqueous solutions of ionic liquids for hydroxyethyl cellulose decreases with increasing temperature and addition of ionic liquids. The flow activation energy was found from the linearization of Arrhenius equation and correlated in terms of polymer concentration. From sign of the initial slope of the activation energy versus polymer concentration at zero concentration, it is concluded that thermodynamic quality of aqueous solutions of ionic liquids are reduced by increasing temperature.

Preparation, characterization, dielectric properties and solvent-imbibing behavior of styrene–butadiene rubber/zinc sulfide nanocomposites

This work focuses on the preparation of styrene–butadiene rubber (SBR)/zinc sulfide (ZnS) nanocomposites using a simple and inexpensive two-roll mill mixing technique. The structural, morphological and thermal properties of the nanocomposites were analyzed by FT-IR, UV–visible spectroscopy, XRD, SEM and DSC measurements. The results of the spectroscopic studies revealed the interaction of ZnS nanoparticles with SBR through the shift in the peaks of UV and FT-IR spectra. The XRD and SEM studies showed that the nanoparticles were well inserted into the macromolecular structure of SBR. The glass transition temperature of the composites increased with the addition of nanoparticles. The dielectric constant of nanocomposite with different loading of nanoparticles was carried out in the frequency range 100–106 Hz. The dielectric properties of nanocomposites were higher than that of pure SBR. In addition, the diffusion and transport properties of organic solvents through SBR/ZnS nanocomposites were studied in detail as a function of ZnS content. The polymer–solvent interaction parameter, enthalpy and entropy of sorption data were estimated from the transport properties. The high dielectric constant of these nanocomposites infers that ZnS is one of the ideal nanofiller for the development of high-k materials for flexible energy storage applications.

Time-Resolved Analysis of Dielectric Mirrors for Vapor Sensing.

Dielectric mirrors based on bilayers of polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene (SEBS) and poly(vinyl alcohol) (PVA)-zirconium dioxide (ZrO2) nanocomposites are fabricated for vapor sensing. When exposed to specific solvent vapor, the layers of dielectric mirrors can gradually swell and cause a red-shift of the reflection band. Because PVA solely responds to water and SEBS is sensitive to several different types of organic solvents, the mirrors can respond to a large variety of solvents. The dual-functional hydrophilic ZrO2 nanoparticles are introduced to not only enlarge the refractive index contrast but also increase the permeability. Time-resolved measurements show that mirrors with nanoparticles have a significantly faster response than those without nanoparticles. Moreover, the dependence on relative humidity is studied for representative solvents, and several types of solvents are selected to show the dependence on the solvent-polymer interaction parameters at typical relative humidity, which allows one to predict the responsivity and selectivity of the sensors.

Contributions of network topological structures to the mechanical properties of PDMS elastomers

Silicone elastomers (poly dimethyl siloxane, PDMS) are widely used in the fabrication of MEMS devices and in mechanobiological studies. Mechanical properties of the elastomers may be varied by changing the crosslinking density and physical entanglements in the networks. Other factors like dangling chains and uncrosslinked sol fractions also influence the network mechanics. We investigated the role of crosslinks, entanglements and sol fraction in the mechanical properties of PDMS prepared with different ratios of base to crosslinker. Results from compression tests show greater elastic modulus for the highly crosslinked networks. We removed uncrosslinked sol, altered the entanglement density with xylene extraction, and used data from mechanical tests to assess predictions from the Frenkel-Flory-Rehner model. These studies show that the polymer-solvent interaction parameter, χ, varied linearly with the equilibrium volume fraction. Dynamic mechanical analyses of extracted PDMS samples showed that crosslinking density, solvent presence, and sol fraction affect their overall viscoelasticity properties. We also compared experimental data with scaling laws and demonstrate that trapped entanglements in the networks contribute to the mechanical properties of PDMS. Finally, we show from these studies that swelling behaviors of PDMS in xylene follow affine deformation.