Interactions In Polymer Solutions Research Articles

Modeling Sorption of Hydrocarbons in Polyethylene with the SAFT-γ Mie Approach Combined with a Statistical-Mechanical Model to Describe Semicrystalline Polymers.

A recently developed statistical-mechanical model is applied systematically to estimate the fraction of tie-molecules (polymer chains linking different crystals directly or via entanglements) in semicrystalline polyethylene (PE) samples. The amorphous domains of the polymer are divided into constrained interlamellar domains and "free" outer-lamellar domains. A set of model parameters is assigned to each sample by correlating previous experimental measurements and minimizing the difference between the predicted solubility of pure hydrocarbons in the sample and the experimental values. We show that the sorption isotherms of multiple pure fluids in each sample can be described by a single parameter set, proving that the polymer-solute interactions (described accurately by the SAFT-γ Mie EoS) are decoupled from the sample-specific properties of the polymer. We find that ∼30% of the crystalline stems in the lamellae of PE are connected to tie-molecules, within the bounds suggested by previous theoretical and computational work. The transferability of the sample-specific parameters is assessed by predicting cosolubility effects and solubility at different temperatures, leading to good agreement with experimental data.

Adsorption Energetics of Amino Acid Analogs on Polymer/Water Interfaces Studied by All-Atom Molecular Dynamics Simulation and a Theory of Solutions.

Energetics of adsorption was addressed with all-atom molecular dynamics simulation on the interfaces of poly(2-methoxyethyl acrylate) (PMEA), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) with water. A wide variety of adsorbate solutes were examined, and the free energy of adsorption was computed with the method of energy representation. It was found that the adsorption free energy was favorable (negative) for all the combinations of solute and polymer, and among PMEA, PMMA, and PBA, the strongest adsorption was observed on PMMA for the hydrophobic solutes and on PMEA for the hydrophilic ones. According to the decomposition of the adsorption free energy into the contributions from polymer and water, it was seen that the polymer contribution is larger in magnitude with the solute size. The total free energy of adsorption was correlated well with the solvation free energy in bulk water only for hydrophobic solutes. The roles of the intermolecular interaction components such as electrostatic, van der Waals, and excluded-volume were further studied, and the electrostatic component was influential only in determining the polymer dependences of the adsorption propensities of hydrophilic solutes. The extent of adsorption was shown to be ranked by the van der Waals component in the solute-polymer interaction separately over the hydrophilic and hydrophobic solutes, with the excluded-volume effect from water pointed out to also drive the adsorption.

Implanting an ion-selective “skin” in electrolyte towards high-energy and safe lithium-sulfur battery

•Highly crosslinked structures enable reversible sulfur electrochemistry •Ion electrokinetic regulation enables uniform Li transport against dendritic growth •Li-S pouch cell with high specific energy, enhanced safety, and cycling performance Ion electrokinetic regulation in electrolyte is of great significance to alleviating polysulfide shuttling and dendritic growth in lithium-sulfur (Li-S) batteries. Inspired by the tunable solute-polymer interactions of ion exchange membrane, herein we implant an ion-selective “skin” constructed by isocyanoethyl methacrylate grafted polyethylenimine (PEI-IEM) in electrolyte via in situ gelation. This tailored skin endows the PEI-IEM-based gel polymer electrolyte (GPE) with a hyper-branched network with abundant polar groups, thus upgrading the electrolyte flame resistance, realizing obstruction on polysulfide migration, and facilitating Li+ transport against uneven deposition. Consequently, the PEI-IEM-based GPE empowers enhanced S electrochemical reversibility and high security, as evidenced by a 10 Ah Li-S pouch cell with a low electrolyte/S ratio of 2.6 and 1.4× excess Li anode that delivers an energy density of 412.7 Wh kg−1. This proof-of-concept study provides new insights for tailoring the ionic behaviors of electrolyte to achieve high-energy and safe Li-S batteries. Ion electrokinetic regulation in electrolyte is of great significance to alleviating polysulfide shuttling and dendritic growth in lithium-sulfur (Li-S) batteries. Inspired by the tunable solute-polymer interactions of ion exchange membrane, herein we implant an ion-selective “skin” constructed by isocyanoethyl methacrylate grafted polyethylenimine (PEI-IEM) in electrolyte via in situ gelation. This tailored skin endows the PEI-IEM-based gel polymer electrolyte (GPE) with a hyper-branched network with abundant polar groups, thus upgrading the electrolyte flame resistance, realizing obstruction on polysulfide migration, and facilitating Li+ transport against uneven deposition. Consequently, the PEI-IEM-based GPE empowers enhanced S electrochemical reversibility and high security, as evidenced by a 10 Ah Li-S pouch cell with a low electrolyte/S ratio of 2.6 and 1.4× excess Li anode that delivers an energy density of 412.7 Wh kg−1. This proof-of-concept study provides new insights for tailoring the ionic behaviors of electrolyte to achieve high-energy and safe Li-S batteries.

Preparation of Polypropylene/silver nanoparticles Nanocomposite films and Evaluation of its Barrier and Antimicrobial Properties for Packaging Applications

Polymeric films which can be used in packaging industries were prepared by blown film method with polypropylene chips and silver nanoparticles. The nanocomposite films were characterized concerning its potential use. Oxygen Transmission rate (OTR) measurements was done in order to ascertain permeability of oxygen through the polymeric films. It was found that the permeability of oxygen through nanocomposite film is higher than that of virgin polypropylene film due to incompatibility between polypropylene matrix and silver nanoparticles. The water vapour transmission rate (WVTR) test of the polymeric nanocomposite films was calculated in order to know the information about mass transfer mechanisms and solute-polymer interactions in the food packaging film. It has been found that, there is a significant decreased water vapour transmission rate through nanocomposite films compared to that of virgin polypropylene film. With increasing the concentration of silver nanoparticles, this effect was reduced. The explanation for this could be that with higher concentration of silver nanoparticles agglomeration in the polymer film could the possibility which create narrow pathway for water molecules to travel. The effect of various silver nanoparticles content in the polymer nanocomposites with respect to its antimicrobial efficacy against the Gram positive bacteria Escherichia coli and Gram positive bacteria Staphylococcus aureus were studied. However, Escherichia coli was most effectively retarded by silver nanoparticles than Staphylococcus aureus, which is related to the difference in the cell wall of the gram positive and gram negative bacteria.

Tuning the permeability of regular polymeric networks by the cross-link ratio.

The amount of cross-linking in the design of polymer materials is a key parameter for the modification of numerous physical properties, importantly, the permeability to molecular solutes. We consider networks with a diamond-like architecture and different cross-link ratios, concurring with a wide range of the polymer volume fraction. We particularly focus on the effect and the competition of two independent component-specific solute-polymer interactions, i.e., we distinguish between chain-monomers and cross-linkers, which individually act on the solutes and are altered to cover attractive and repulsive regimes. For this purpose, we employ coarse-grained, Langevin computer simulations to study how the cross-link ratio of polymer networks controls the solute partitioning, diffusion, and permeability. We observe different qualitative behaviors as a function of the cross-link ratio and interaction strengths. The permeability can be tuned ranging over two orders of magnitude relative to the reference bulk permeability. Finally, we provide scaling theories for the partitioning and diffusion that explicitly account for the component-specific interactions as well as the cross-link ratio and the polymer volume fraction. These are in overall good agreement with the simulation results and grant insight into the underlying physics, rationalizing how the cross-link ratio can be exploited to tune the solute permeability of polymeric networks.

Critical Depletion, Adsorption, and Intersurface Interaction in Polymer Solutions: A Mean-Field Theory Study

Using a self-consistent field theory, we examine the thermodynamics and interfacial properties of a homopolymer solution, either close to a single hard surface or confined between two parallel surfaces, in equilibrium with a bulk reservoir. We focus on the bulk critical regime and find that various physical quantities therein exhibit qualitatively different behaviors from those in the off-critical regime. For the single-surface system, the surface-excess Γ diverges as ln|ϕb – ϕc| and ln|χc – χ| when approaching the bulk critical point, where χ and ϕb are the Flory–Huggins interaction parameter and the volume fraction of polymer segment in bulk solution, respectively, and χc and ϕc are their respective values at the critical point. Γ diverges to +∞ when the surface–polymer interaction eₛ is larger than the depletion–adsorption transition (DAT) point ec, and to −∞ when eₛ < ec. As such, the DAT at ec in the critical regime is rather sharp and ec = 0.1824 + 0.1359N–¹/² at large N. For the two-surface system, the intersurface potential W at the critical point is purely attractive for both depleted and adsorbed cases and follows a D–³ power-law decay at large intersurface separations D; when eₛ is close to ec, the strength of W becomes rather weak. This nonmonotonic dependence of W on eₛ has important experimental implications on the stability of colloidal suspensions.

Multi-region finite element modelling of drug release from hydrogel based ophthalmic lenses

Understanding the way in which drug is released from drug carrying hydrogel based ophthalmic lenses aids in the development of efficient ophthalmic drug delivery. Various solute–polymer interactions affect solute diffusion within hydrogels as well as hydrogel–bulk partitioning. Additionally, surface modifications or coatings may add to resistance of mass transfer across the hydrogel interface. It is necessary to consider both interfacial resistances as well as the appropriate driving force when characterizing interface flux. Such a driving force is induced by a difference in concentration which deviates from equilibrium conditions. We present a Galerkin finite element approach for solute transport in hydrogels which accounts for diffusion within the gel, storage effects due to polymer–solute interaction, as well as partitioning and mass transfer resistance effects at the interface. The approach is formulated using a rotational symmetric model to account for realistic geometry. We show that although the resulting global system is not symmetric in the case of partitioning, it is similar to a symmetric negative semidefinite system. Thus, it has non-positive real eigenvalues and is coercive, ensuring the validity of the finite element formulation as well as the numerical stability of the implicit backward Euler time integration method employed. Two models demonstrating this approach are presented and verified with release experimental data. The first is the release of moxifloxacin from intraocular lenses (IOLs) plasma grafted with different polyacrylates. The second accounts for both loading as well as the release of diclofenac from disc shaped IOL material loaded for varied time periods and temperature.

Simulating the Effects of Excluded-Volume Interactions in Polymer Solutions

Excluded-volume interactions are ubiquitous to modeling the average size of polymers in solution. This paper shows how simulations can be used by students to explore the emergence of mathematical scaling relations from excluded-volume interactions. Simulations provide robust visual representations of the system, and can be used to investigate a wide scope of problems and scenarios. The simulations were built with the free VPython coding environment and relatively basic algorithms. The results align with the mathematical theories of Flory and De Gennes and provide access to additional insights that are less obvious in the mathematical treatments. Students with relatively basic programming knowledge were able to extend and modify these models and to examine their alignment with mathematical theories. These examples extend the growing literature on simulation-based approaches for teaching and learning chemistry.

The Effect of Intramolecular Cross-Linking on Polymer Interactions in Solution.

The conformation of a polymer in a solvent is typically defined by the solvent quality, which is a consequence of the solvent and macromolecule's chemistry. Yet, additional factors can affect the polymer conformation, such as non-covalent interactions to surfaces or other macromolecules, affecting the amount of polymer-solvent interactions. Herein, chemically folded polymers with protein-like architectures are studied and compared to their unfolded linear precursor in good solvents using rheology measurements. The current research reveals that permanent folding by intramolecular chemical cross-linking limits the chain mobility and therefore causes a reduction in polymer-solvent interactions, making a good solvent become theta. This change not only affects the "solvent quality" but also leads to a change in particle-particle interactions as a function of concentration. These findings provide crucial insight into the effects of intramolecular cross-links on macromolecule solubility and self-assembly, which are critical for mimicking structurally similar biological materials.

Distinct alignment of benzene derivatives in stretched polystyrene and polybutylacrylate gels: Specific polymer-solute interactions.

We have measured the alignment of a range of benzene derivatives in cross-linked polystyrene and poly(butyl acrylate) using a small number of residual dipolar couplings and simple geometric considerations. For apolar solutes in polystyrene and protic solutes in poly(butyl acrylate), the preferred molecular orientation does not coincide with the longest molecular axis (steric aligment). This behavior may be explained by specific π-π and hydrogen bonding interactions between solute and polymer, respectively, the latter being confirmed by molecular dynamics simulations.

Quantifying the Interactions in the Aggregation of Thermoresponsive Polymers: The Effect of Cononsolvency.

The aggregation kinetics of thermoresponsive core-shell micelles with a poly(N-isopropyl acrylamide) shell in pure water or in mixtures of water with the cosolvents methanol or ethanol at mole fractions of 5% is investigated during a temperature jump across the respective cloud point. Characteristically, these mixtures give rise to cononsolvency behavior. At the cloud point, aggregates are formed, and their growth is followed with time-resolved small-angle neutron scattering. Using the reversible association model, the interaction potential between the aggregates is determined from their growth rate in dependence on the cosolvents. The effect of the cosolvent is attributed to the interaction potential on the structured layer of hydration water around the aggregates. It is surmised that the latter is perturbed by the cosolvent and thus the residual repulsive hydration force between the aggregates is reduced. The larger the molar volume of the cosolvent, the more pronounced is the effect. This framework provides a molecular-level understanding of solvent-mediated effective interactions in polymer solutions and new opportunities for the rational control of self-assembly in complex soft matter systems.

Effect of calcium/sodium ion exchange on the osmotic properties and structure of polyelectrolyte gels.

We discuss the main findings of a long-term research program exploring the consequences of sodium/calcium ion exchange on the macroscopic osmotic and elastic properties, and the microscopic structure of representative synthetic polyelectrolyte (sodium polyacrylate, (polyacrylic acid)) and biopolymer gels (DNA). A common feature of these gels is that above a threshold calcium ion concentration, they exhibit a reversible volume phase transition. At the macroscopic level, the concentration dependence of the osmotic pressure shows that calcium ions influence primarily the third-order interaction term in the Flory-Huggins model of polymer solutions. Mechanical tests reveal that the elastic modulus is practically unaffected by the presence of calcium ions, indicating that ion bridging does not create permanent cross-links. At the microscopic level, small-angle neutron scattering shows that polyacrylic acid and DNA gels exhibit qualitatively similar structural features in spite of important differences (e.g. chain flexibility and chemical composition) between the two polymers. The main effect of calcium ions is that the neutron scattering intensity increases due to the decrease in the osmotic modulus. At the level of the counterion cloud around dissolved macroions, anomalous small-angle X-ray scattering measurements made on DNA indicate that divalent ions form a cylindrical sheath enveloping the chain, but they are not localized. Small-angle neutron scattering and small-angle X-ray scattering provide complementary information on the structure and interactions in polymer solutions and gels.

Nanoconfinement and Chemical Structure Effects on Permeation Selectivity of Self-Assembling Graft Copolymers.

Permeation of small molecule solutes through thin films is typically described by the solution-diffusion model, but this model cannot predict the effects of nanostructure due to self-assembly or additives. Other models focusing on diffusion through isolated nanopores indicate that confining permeation to channels slightly larger than the size of the solute can lead to an increased influence of solute-pore wall interactions on permeation rate. In this study, we analyze how differences in polymer nanostructure affect the relative contributions of solute size and polymer-solute interactions on transport rate. We compared the diffusion rates of several small molecules through two polymer thin films: A cross-linked, homogeneous film of poly(ethylene glycol phenyl ether acrylate) (PEGPEA) and a graft copolymer with a poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-co-CTFE)) backbone and PEGPEA side chains that self-assemble into continuous ∼1-3 nm PEGPEA domains through which transport occurs. We correlated these rates with the size of each solute and its chemical affinity to PEGPEA, as measured by the difference between their solubility parameters. Diffusion rate through the homogeneous polymer film was controlled by solute size, whereas diffusion rate through the copolymer was strongly controlled by the difference between the solubility parameters. Furthermore, permeation selectivity between two selected molecules was 2.5× higher for the nanostructured copolymer, likely enhanced by the nanoconfinement effects. These initial results indicate that polymer self-assembly is a promising tool for designing polymeric membranes that can differentiate between solutes of similar size but differing chemical structures.

Photoisomerization of trans-Stilbene in Poly(vinyl alcohol) and Importance of Solute–Polymer Interactions

Abstract We have measured the polarized absorption and picosecond transient absorption spectra of trans-stilbene in poly(vinyl alcohol) (PVA) films. We found that the dichroic ratio in the first absorption band and the lifetime of the S1 state increased as the hold-time was increased. The hold-time is the duration in which sample films were kept wet before they were dried. For similar values of the hold-time, the absorption spectra showed a red shift and slight sharpening. These results indicate that during the hold-time, solute–polymer interactions become strong; these interactions not only act as the orienting force during film stretching but also act as friction that opposes isomerization.

Biocompatible Alginate Microgel Particles as Heteronucleants and Encapsulating Vehicles for Hydrophilic and Hydrophobic Drugs

Biocompatible materials that can control crystallization while carrying large amounts of active pharmaceutical ingredients (APIs) with diverse chemical properties are in demand in industrial practice. In this study, we investigate the utility of biocompatible alginate (ALG) hydrogels as a rational material for crystallizing and encapsulating model APIs that present drastically different solubilities in water. Acetaminophen (ACM) and fenofibrate (FEN) are utilized as the model hydrophilic and hydrophobic moieties, respectively. ALG hydrogels with different ALG concentrations (hence different mesh sizes) are utilized as heteronucleants to control the nucleation kinetics of ACM from solution. ALG hydrogels with smaller mesh sizes showed faster nucleation kinetics. We hypothesize that this behavior is due to the interplay between the polymer–solute interactions and the mesh-induced confinement effects. The loading of ACM into hydrogels by equilibrium partitioning is quantified and found to be inversely proportional to ALG concentration. For hydrophobic model APIs, loading via equilibrium partitioning is inefficient; hence, we suggest emulsion-laden hydrogels where emulsion droplets are encapsulated inside the hydrogel matrix. The incorporation of emulsion droplets inside hydrogels enables the high loading of the hydrophobic API leveraging the high solubility of the hydrophobic API in the dispersed emulsion droplets. By carefully choosing the emulsification method and the dispersed phase, we demonstrate significant loading (up to ∼80% w/w) and crystallization of the stable form of FEN. Our results provide new insights for designing biocompatible nucleation-active materials capable of carrying industrially significant amounts of water-soluble and insoluble APIs in the crystalline form.

Polymer-Induced Selective Nucleation of Mono or Ortho Polymorphs of Paracetamol through Swift Cooling of Boiled Aqueous Solution

A novel method of inducing the preferred polymorph of paracetamol through swift cooling of boiled aqueous solution in the presence of selective polymers has been identified. Depending upon the molecular interaction between the selected polymers such as nylon 6/6, polypropylene, and polyvinylchloride and the paracetamol, nucleation of either mono or ortho or both polymorphic forms of paracetamol were induced at well-distinguished supersaturation regions, whereas in the absence of the polymers, pure aqueous solution yielded only stable mono form. Nucleations induced by three different polymers have different induction periods. The percentage of mono, ortho, and mixed polymorphs nucleated at different supersaturation regions was estimated. Their external morphologies were identified through optical in situ microscopy, and their internal crystallographic structure was confirmed by powder X-ray diffraction (PXRD). It is found that the specific polymer–solute interaction induces nucleations with preferential gr...

Solution structure: defining polymer film morphology and optoelectronic device performance

Film structure plays a critical role in defining the performance of all organic optoelectronic devices, with the importance clearly illustrated in the development of organic acceptor–donor bulk heterojunction (BHJ) photovoltaic (OPV) devices where solvent and/or thermal annealing of the deposited active layer affect solar cell output. Herein we report that the polymer–polymer interactions in solution, which are dependent on the thermal history of the solution, are a first order parameter in controlling the properties of the final active layer and hence device performance. We illustrate the key role played by organic semiconductor interactions in solution with the high efficiency donor–acceptor co-polymer, poly[N-9′′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), and its blends with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Differences in the cooling rate of the casting solution after dissolution can lead to a 20% variation in the ultimate efficiency of cells with identical active layer thicknesses with slow-cooled solutions giving rise to poorer devices. The oft-ignored intermolecular (polymer–polymer) interactions that occur in solution are manifest by dramatic differences in viscosity and are a function of concentration and molecular weight. Hence solution thermal history represents a critical new dimension in the processing landscape for organic polymer semiconductors.

Fluorescent polymer coatings with tuneable sensitive range for remote temperature sensing

Polymer films of poly(vinyl alcohol) containing the fluorescent dyes 4-aminophthalimide (AP) or 6-propionyl-2-dimethylamino-naphthalene (Prodan) are used as temperature-sensitive fluorescent coatings for remote temperature sensing. Temperature can be obtained by a two-wavelength ratiometric-based emission intensity measurement. The coatings are sensitive in a 100K temperature range that can be tuned by polymer–solute interactions. The usable range is 200–300K for AP and 280–380K for Prodan.

Maintaining Supersaturation in Aqueous Drug Solutions: Impact of Different Polymers on Induction Times

The use of polymeric additives is an increasingly common approach for inhibiting crystallization from the supersaturated solutions used to enhance the delivery of poorly water-soluble drugs. Maintaining supersaturation by employing polymeric additives depends on their ability to inhibit nucleation and crystal growth. In solution crystallization, nucleation initiates the process of crystallization, and therefore adequate control over crystallization from supersaturated solutions cannot be achieved without understanding the mechanism of nucleation inhibition by polymers. In this study, the effectiveness of a group of chemically diverse polymers, including several recently synthesized cellulose derivatives, on induction times in aqueous solutions was quantified. Nucleation was quantified by measuring the induction time for the appearance of particulates from unseeded desupersaturation experiments for three model pharmaceutical compounds: celecoxib, efavirenz, and ritonavir. Induction times in the absence of the polymers varied from approximately 2 min for celecoxib to 2 h for ritonavir. Some polymers were found to extend induction times by up to a factor of 5–6 at the highest supersaturations tested. The effectiveness of the various polymers appeared to depend on the hydrophobicity of the polymer relative to that of the drug. The hydrophobicity of the polymer most likely influences the ability of the polymer to form polymer–solute interactions relative to polymer–solvent and polymer–polymer interactions. Polymer–solute interactions would be expected to hinder the reorganization of a cluster of solute molecules into an ordered crystal structure.

STUDY OF THERMODYNAMICAL PROPERTIES OF POLYVINYL ACETATE IN TETRAHYDROFURAN

The propagation of ultrasonic waves and the measurement of their velocity in solutions form an important tool for the evaluation of various acoustical and thermodynamical parameters which give an insight into the nature of miscibility and molecular interactions in polymer solutions. In the present study, the ultrasonic velocity, density, viscosity measurements have been made in 0.1 M solution using pulse echo overlap technique at 293 K at the different concentrations of polyvinyl acetate in tetrahydrofuran. Thermo-acoustical parameters viz., adiabatic compressibility, molar sound velocity, molar compressibility, expansion coefficient, acoustic impedance, van der Waals' constant and internal pressure have been computed from the experimental data. The nature of polymer/solvent interaction and the effect of concentration on the molecular interaction are studied. The nonlinear variations of polyvinyl acetate in tetrahydrofuran have been studied. The variation of ultrasonic velocity and other thermo-acoustical parameters shows nonlinear increase or decrease with molar concentration which suggest semi-compatibility of the polymer in the given solvent.