Water Interaction Parameter Research Articles

Stimuli‐Responsive Hydrogels Based on Random Copolymers of the Sucrose Methacrylate

AbstractPoly(sucrose methacrylate‐co‐acrylic acid), P(SMA‐co‐AA), and poly(sucrose methacrylate‐co‐diethylene glycol methyl ether methacrylate), P(SMA‐co‐EG2MA), are synthesized by free radical polymerization using sucrose dimethacrylate as a crosslinker. The copolymers present one glass transition suggesting a random distribution of the comonomers. The copolymers–water interaction parameter χ is around 0.5, while Mc increases with SMA molar fraction. The kinetics of water swelling show a Fickian behavior for P(SMA‐co‐AA) richer in acrylic acid. The swelling is driven by the ionic character of the P(SMA‐co‐AA), except at pH = 2, and by the hydrophilicity of the SMA for the P(SMA‐co‐EG2MA). The temperature influences the swelling behavior of the P(SMA‐co‐EG2MA) due to the lower critical solution temperature (LCST) behavior. The pH‐ and thermoresponsiveness of the P(SMA‐co‐AA) and P(SMA‐co‐EG2MA) hydrogels are maintained by replacing the sensitive comonomers with SMA up to mass fractions of 85 and 20 wt%, respectively, ≈71 and 17 wt% of sucrose, a product from a renewable resource. The hydrolytic degradation of the hydrogels is more pronounced for copolymers richer in SMA and resulted in sucrose release. Hydrogels present viscoelastic behavior, and the P(SMA‐co‐AA) series is more resistant to compression. The xerogels of the copolymers richer in SMA show a foam‐like morphology with open cells.

Solubility Calculations of Methane and Ethane in Aqueous Electrolyte Solutions

Accurate calculation of light hydrocarbon solubilities in aqueous electrolyte solutions is critical for petroleum and geochemical applications. However, very few electrolyte Equations of State (e-EoS) have been used for calculation of light hydrocarbon solubilities. Thermodynamic calculation of gas (methane and ethane) solubilities in aqueous solutions of chloride salts are presented. This work introduces a new parameter estimation approach (which can predict well the liquid densities of aqueous solutions) for the electrolyte Cubic Plus Association EoS (e-CPA). The cation/anion–water interaction parameters are obtained from the regression of experimental mean ionic activity coefficients and liquid densities. The results show that the e-CPA with the new parameter estimation approach gives good agreements with the corresponding experimental data. The cation/anion–gas interaction parameters are obtained from the regression of experimental gas solubilities. The results show that the e-CPA with the new parameter estimation approach correlates the gas solubilities reasonably well. The gas dissolution mechanisms and salting effects are extensively analyzed and discussed for a deeper understanding of gas dissolution in aqueous electrolyte solutions.

Molybdenum disulfide and water interaction parameters.

Understanding the interaction between water and molybdenum disulfide (MoS2) is of crucial importance to investigate the physics of various applications involving MoS2 and water interfaces. An accurate force field is required to describe water and MoS2 interactions. In this work, water-MoS2 force field parameters are derived using the high-accuracy random phase approximation (RPA) method and validated by comparing to experiments. The parameters obtained from the RPA method result in water-MoS2 interface properties (solid-liquid work of adhesion) in good comparison to the experimental measurements. An accurate description of MoS2-water interaction will facilitate the study of MoS2 in applications such as DNA sequencing, sea water desalination, and power generation.

Electrolyte-UNIQUAC-NRF Model Based on Ion Specific Parameters for the Correlation of Mean Activity Coefficients of Electrolyte Solutions

The Electrolyte-UNIQUAC-NRF excess Gibbs function was applied to estimate ion specific adjustable parameters of various salts by global optimization of the experimental activity coefficients of 54 electrolyte solutions. Twenty-three ion specific parameters were obtained for water and several cations and anions. The estimated individual ion parameters have been used to predict osmotic coefficient of electrolyte solutions. By using only the specific values for ions, the anion–cation and ion–water interaction parameters of different salts can be precisely estimated. Consequently, the interaction parameters of sparingly insoluble salts without experimental activity data can be easily calculated. For a case study, the solubility of CaSO4 was predicted in relatively good agreement with experimental values over a wide range of temperatures up to 473.18 K.

The structural, morphological and thermal properties of grafted pH-sensitive interpenetrating highly porous polymeric composites of sodium alginate/acrylic acid copolymers for controlled delivery of diclofenac potassium

In present investigation new formulations of Sodium Alginate/Acrylic acid hydrogels with high porous structure were synthesized by free radical polymerization technique for the controlled drug delivery of analgesic agent to colon. Many structural parameters like molecular weight between crosslinks (Mc), crosslink density (Mr), volume interaction parameter (v2,s), Flory Huggins water interaction parameter and diffusion coefficient (Q) were calculated. Water uptake studies was conducted in different USP phosphate buffer solutions. All samples showed higher swelling ratio with increasing pH values because of ionization of carboxylic groups at higher pH values. Porosity and gel fraction of all the samples were calculated. New selected samples were loaded with the model drug (diclofenac potassium).The amount of drug loaded and released was determined and it was found that all the samples showed higher release of drug at higher pH values. Release of diclofenac potassium was found to be dependent on the ratio of sodium alginate/acrylic acid, EGDMA and pH of the medium. Experimental data was fitted to various model equations and corresponding parameters were calculated to study the release mechanism. The Structural, Morphological and Thermal Properties of interpenetrating hydrogels were studied by FTIR, XRD, DSC, and SEM.

Molecular Dynamics Simulation of the Effects of the Carbon–Water Interaction Parameters on the Nanofluidic Energy Absorption System

In this paper, the effects of the energy (e) and distance (σ) parameters of Lennard-Jones potential in carbon–water interaction on the nanofluidic energy absorption system are investigated using molecular dynamics simulation. These parameters show the strength of the interactions between carbon nanotube (CNT) and water. For this purpose, six values for each of e and σ used in the previous works are considered. The results show that the hydrophobic intensity of CNT is decreased by increasing each of the interaction parameters. The CNT surface at (e = 0.0599 kcal/mol and e = 0.06461 kcal/mol) and e = 0.1349 kcal/mol, at all σ’s, is obtained as hydrophobic and hydrophilic, respectively. For e between 0.06461 and 0.1349 kcal/mol, the CNT surface is changed from hydrophobic to hydrophilic by increasing σ from 3.126 to 3.835 A. When CNT surface is hydrophobic, contact angle, infiltration pressure, and absorbed energy is reduced by increasing each of the interaction parameters.

Hexagonal boron nitride and water interaction parameters.

The study of hexagonal boron nitride (hBN) in microfluidic and nanofluidic applications at the atomic level requires accurate force field parameters to describe the water-hBN interaction. In this work, we begin with benchmark quality first principles quantum Monte Carlo calculations on the interaction energy between water and hBN, which are used to validate random phase approximation (RPA) calculations. We then proceed with RPA to derive force field parameters, which are used to simulate water contact angle on bulk hBN, attaining a value within the experimental uncertainties. This paper demonstrates that end-to-end multiscale modeling, starting at detailed many-body quantum mechanics and ending with macroscopic properties, with the approximations controlled along the way, is feasible for these systems.

ChemInform Abstract: Ion Specific Effects: Decoupling Ion‐Ion and Ion‐Water Interactions

AbstractReview: 110 refs.

Structural and interaction parameters of thermosensitive native α-elastin biohybrid microgel

The structural and water interaction parameters for native, α-elastin biohybrid microgel crosslinked with hydrophilic and hydrophobic crosslinkers are obtained from the volume phase transition temperature behaviour, 1H high-resolution magic-angle sample spinning transverse magnetization relaxation NMR, and modified Flory–Rehner swelling theory. Firstly, considering a homogeneous morphology the number of subchains in the biohybrid microgel, the residual water in deswollen state as a function of crosslink density and the temperature dependence of the Flory biopolymer–water interaction parameters are reported for the biohybrid microgels prepared with hydrophilic (PEG-DGE) and hydrophobic (BS3) crosslinkers. The Flory–Rehner classical approach is subsequently modified taking into account the heterogeneities observed by NMR transverse relaxation measurements. Two differently mobile regions are determined, a hydrophobic domain and a crosslinking domain with relative reduced mobility. For the first time, the influence of chain mobility on the Flory interaction parameter is investigated through a modified Flory state equation. The contributions of amino-acids located in the hydrophobic and crosslinking domains in the polypeptide sequence are separated while analyzing the biopolymer–water interaction.

Automated Optimization of Water–Water Interaction Parameters for a Coarse-Grained Model

We have developed an automated parameter optimization software framework (ParOpt) that implements the Nelder–Mead simplex algorithm and applied it to a coarse-grained polarizable water model. The model employs a tabulated, modified Morse potential with decoupled short- and long-range interactions incorporating four water molecules per interaction site. Polarizability is introduced by the addition of a harmonic angle term defined among three charged points within each bead. The target function for parameter optimization was based on the experimental density, surface tension, electric field permittivity, and diffusion coefficient. The model was validated by comparison of statistical quantities with experimental observation. We found very good performance of the optimization procedure and good agreement of the model with experiment.

On Interfacial Tension at a Rigid Apolar Wall–Water Interface

Evidence is presented that the interfacial tension or excess free energy per unit area of the planar interface between extensive, rigid, apolar walls and modeled water is an arithmetic sum of three independent quantities: the surface tension of water, the contribution of the integrated wall-water dispersion interaction, and the contribution of the net exclusion volume associated with the rigid, noninteracting wall. The fact that the interfacial tension is linearly dependent on the wall-water interaction parameter is the inspiration for two conjectures: the interfacial water structure is independent of ε(SL), and the mean interfacial water density profile is not a measure of the interfacial water structure.

Network parameters of poly(N‐isopropylacrylamide)/montmorillonite hydrogels: effects of accelerator and clay content

AbstractThe results of network parameters of poly(N‐isopropylacrylamide)/montmorillonite (PNIPAAm/MMT) hydrogels prepared with two different types and concentrations of accelerators (tetramethylethylenediamine, TEMED and quaternary TEMED containing decyl bromide, QTEMED) using three different clay contents (1.0, 3.0, and 5.0 wt% of total monomer concentration) at two different polymerization temperatures (10 and 32°C) were presented and discussed. It was observed that when the reaction temperature of PNIPAAm crosslinked with MMT was chosen as 10°C both volume swelling ratios (i.e., thermodynamic interaction) and shear moduli, G increased. In hydrogels, thermodynamic interaction is reflected by polymer–water interaction parameter (χ). The lower is the value of χ, the stronger is the interaction between polymer and water, and the lower is the interaction between hydrophobic groups or between polymer chains. In addition, increase in MMT content was slightly affected on these intermolecular interactions. Therefore, this effect that combines high‐shear modulus with lower value of χ in the same molecular structure was defined as clay content‐independent diffusion behavior. On the other hand, in the case of the hydrogels synthesized with the higher concentration of TEMED and MMT, the values of χ and G decreased. These facts were interpreted that increase in both accelerator concentration and clay content, for fixed NIPAAm concentration made the number of effective crosslinks between MMT layers smaller. Copyright © 2010 John Wiley & Sons, Ltd.

Phase behavior and mechanism of formation of protofiber morphology of solution spun poly(acrylonitrile) copolymers in DMF-water system

Phase diagrams of a series of copolymers of acrylonitrile (AN) and acrylic acid (AAc) were constructed using linearized cloud point correlation. The miscibility region in the phase diagram was found to increase with the increase in AAc content of the copolymers. For various compositions, χ13 (polymer–water interaction parameter) values were estimated by sorption experiment. As the hydrophilic nature of the polymer increased with the increase in the content of acrylic acid, the χ13 interaction parameter was found to decrease from poly(acrylonitrile) homopolymer to its copolymer with 50 mol % acrylic acid (AA50B). The polymer–solvent interaction parameters (χ23) and composition at the critical points for all the polymers were determined by fitting the theoretical bimodal curves to the experimental cloud point curves using Kenji Kamide equations. The polymer composition at the critical point was found to increase by 400% with increasing AAc content. The polymers were solution spun in DMF-water coagulation bath at 30°C and their protofiber structures were investigated under scanning electron microscopy. The observed morphological differences in protofibers were explained on the changes brought about in the phase separation behavior of the polymer–solvent–nonsolvent systems. The copolymers with higher acrylic acid content could be solution spun into void free homogeneous fibers even at conditions that produced void-filled inhomogeneous fibers in poly(acrylonitrile) and its copolymers with lower AAc content. The experiments demonstrate the important role of thermodynamics in deciding the protofiber morphology during coagulation process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Investigation of swelling and network parameters of poly(ethylene glycol)-crosslinked poly(methyl vinyl ether- co-maleic acid) hydrogels

The influence of poly(ethylene glycol) (PEG) plasticiser content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether- co-maleic acid) was investigated using thermal analysis, swelling studies, scanning electron microscopy (SEM) and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy revealed a shift of the C O peak from 1708 to 1731 cm −1, indicating that an esterification reaction had occurred upon heating, thus producing crosslinked films. Higher molecular weight PEGs (10,000 and 1000 Da, respectively), having greater chain length, producing hydrogel networks with lower crosslink densities and higher average molecular weight between two consecutive crosslinks. Accordingly, such materials exhibited higher swelling rates. Hydrogels crosslinked with a low molecular weight PEG (PEG 200) showed rigid networks with high crosslink densities and, therefore, lower swelling rates. Polymer:plasticizer ratio alteration did not yield any discernable patterns, regardless of the method of analysis. The polymer–water interaction parameter ( χ ) increased with increases in the crosslink density. SEM studies showed that porosity of the crosslinked films increased with increasing PEG MW, confirming what had been observed with swelling studies and thermal analysis, that the crosslink density must be decreased as the M w of the crosslinker is increased. Hydrogels containing PMVE/MA/PEG 10,000 could be used for rapid delivery of drug, due to their low crosslink density. Moderately crosslinked PMVE/MA/PEG 1000 hydrogels or highly crosslinked PMVE/MA/PEG 200 systems could then be used in controlling the drug delivery rates. We are currently evaluating these systems, both alone and in combination, for use in sustained release drug delivery devices.

Correlations of Thermodynamic Properties of Aqueous Amino Acid-Electrolyte Mixtures

Suitable equations have been proposed to correlate thermodynamic properties, like mean ion activity coefficients, volumes and compressibilities, of amino acids in electrolyte solutions. An amino acid–electrolyte–water interaction parameter is extracted from the regression of the amino acid property values in aqueous electrolyte solution that is then transferred to an expression to correlate the properties of the electrolyte in mixtures. The single interaction parameter can successfully correlate the published data on mean ion activity coefficients, apparent molar volumes and compressibilities of amino acids as well as of electrolytes in their aqueous mixtures. The equations are tested against the large number of experimental data sets available in the literature.

Kinetics and thermodynamics of the water sorption of 2‐hydroxyethyl methacrylate/styrene copolymer hydrogels

AbstractA series of polymer hydrogels based on 2‐hydroxylethyl methacrylate and styrene were synthesized by bulk polymerization. The kinetic and thermodynamic swelling properties of these hydrogels were studied. The swelling mechanism of the hydrogels followed Fickian behavior. The diffusion coefficients, initial swelling rate, and maximum water uptake all decreased with the styrene content increasing because of the hydrophobicity of styrene. The swelling process was exothermic from 278 to 315 K, and the greater the styrene content was, the lower the enthalpy of mixing was in magnitude. The polymer–water interaction parameter, reflecting thermodynamic interactions, increased with increasing styrene content in the polymers. The negative values and trend of the actual partial molar enthalpy and entropy of dilution could be explained by the structuring of water through enhanced hydrogen bonding and hydrophobic interactions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Network and thermodynamic properties of hydrogels of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine

Samples of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (PSPV) have been synthesized to high conversion by free radical polymerization in aqueous solution of the zwitterionic monomer SPV with several concentrations of the crosslinker N, N′-methylene-bis-acrylamide (MBA). Hydrogels obtained by swelling them in water and aqueous KSCN solution were examined by gravimetric and dimensional analysis, and by compression–strain measurements. The derived effective crosslinking density ν e was only ca. 11% of the theoretical value, indicating low efficiency of chemical crosslinking by MBA. At 298 K increasing content of MBA produces increases in the values of ν e, elastic moduli and polymer–water interaction parameter χ. At a fixed MBA content, increasing temperature led to decreases in the values of ν e, elastic moduli and χ, but an increase in water content of hydrogel. For swelling in aq. KSCN solution the mechanical properties are insensitive to content of salt. Experimental and theoretical analysis afforded values of the water/polymer, salt/water and salt/polymer interaction parameters. Where appropriate the findings are compared with those reported for a different zwitterionic hydrogel and a neutral non-zwitterionic hydrogel.

Swelling and network parameters of crosslinked thermoreversible hydrogels of poly( N-ethylacrylamide)

Samples of Poly( N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N, N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression–strain measurements to afford values of swelling ratio, polymer–solvent interaction parameters, elastic moduli and effective crosslinking density ν e. Crosslinking inefficiency is evidenced by the low value (0.23) of ν e relative to the theoretical crosslinking density ν t based on the content of BIS in the synthesis. A small but finite extrapolated value of ν e at ν t = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer–water interaction parameter. At a fixed content of BIS the values of ν e and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of ν e and elastic moduli cf the value in water, has not been resolved satisfactorily.

Phase Behavior and Microdomain Structure in Perfluorosulfonated Ionomers via Self-Consistent Mean Field Theory

This paper describes the use of lattice-based self-consistent mean field (SCMF) theory to predict the equilibrium microstructure in perfluorinated ionomers used as separators in polymer electrolyte membrane (PEM) fuel cells. The SCMF model predicts segregation of ionomer−water mixtures into ionomer-rich and water-rich microdomains as the water content or the fluorocarbon−water interaction parameter (χFW) increases. Phase diagrams and domain structures are reported for water-swollen Nafion, Dow Short Side Chain, a new perfluorosulfonimide, and two other hypothetical ionomers. In general, the phase boundary for melting of the microdomain structure moves to lower values of χFW as the branch density decreases or the branch hydrophilicity increases. For ionomers having the same branch density and branch hydrophilicity, the position of the phase boundary depends on the details of the internal arrangement of chemical groups within the branches. Various phase transitions occur due to segregation of particular ion...

Water vapor absorption into amorphous sucrose‐poly(vinyl pyrrolidone) and trehalose–poly(vinyl pyrrolidone) mixtures

Previous studies from this laboratory suggested that a solution model (Flory–Huggins equation) modified by a free volume model (Vrentas equation) could satisfactorily describe water absorption into an amorphous solid composed of a sugar or a polymer. This paper has extended the studies of single solutes to binary mixtures of trehalose–and sucrose–poly(vinyl pyrrolidone) (trehalose–PVP and sucrose–PVP, respectively) either co‐lyophilized or individually lyophilized and then physically mixed. Water vapor absorption isotherms of the binary mixtures were determined at 30°C. Co‐lyophilized PVP–sugar mixtures take up essentially the same amount of water as predicted by the weight average of individual isotherms, whereas sugar crystallization is significant retarded in the molecular dispersions. The sugar–PVP interaction, as reflected in the Flory–Huggins χ interaction parameter, was estimated by fitting the high relative pressure (p/p0) region of the isotherm, at which the system is in a liquid state, with a three‐component Flory–Huggins‐type model. The estimated sugar–water PVP–water, and sugar–PVP interaction parameters suggest that the solute–water interactions are not significantly affected by the sugar–PVP interaction; that is, the solute–water interaction parameters in a binary solute system are similar to those in the corresponding single solute systems. Based on these interaction parameters, the sucrose–PVP interaction appears to be stronger than that of trehalose–PVP. Manipulation of the interaction parameters suggest that the water vapor absorption isotherm is not a sensitive indicator of possible sugar–PVP interactions. Density, glass transition temperature, Tg, and the heat capacity change, ΔCp, at Tg were determined to estimate the excess water absorption energy due to the plasticizing effect of water using the structural relaxation model, as described by Vrentas. Results suggest that PVP is a better antiplasticizer for sucrose than for trehalose. Consequently, the excess free energy arising from structural relaxation was disproportionally reduced by the presence of PVP in these molecular dispersions. Finally, the entire isotherms of co‐lyophilized sugar–PVP mixtures are reasonably described with an extended three‐component Flory–Huggins model and Vrentas glass structural relaxation model. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1375–1385, 2001