Flory-Huggins Research Articles

Highlighting Thermodynamic Coupling Effects in Alcohol/Water Pervaporation across Polymeric Membranes.

The pervaporation of binary alcohol/water mixtures across polymeric membranes is modeled by combining the Maxwell–Stefan (M-S) diffusion formulation with the Flory–Huggins (F-H) description of sorption equilibrium. The combined M-S/F-H model shows that the flux of each penetrant species is coupled to the driving force of its partner penetrant. Two types of coupling contributions can be distinguished: (i) coupling arising out of correlated motions of penetrants in the polymer matrix and (ii) thermodynamic coupling. The focus of this article is on the contribution of thermodynamic coupling, which is quantified by the set of coefficients , where ai, the activity of species i, is dependent on the volume fractions ϕi,ϕj, of both penetrants in the polymeric membrane. Detailed analyses of published experimental data for pervaporation of ethanol/water feed mixtures of varying compositions in both hydrophobic (poly(dimethylsiloxane)) and hydrophilic (cellulose acetate, polyimide, and polyvinyl alcohol/polyacrylonitrile composite) membranes show that in all cases, the cross-coefficients Γij (i ≠ j) are negative and may attain large magnitudes in relation to the diagonal elements Γii. The net result is that the permeation fluxes of each penetrant are suppressed by its partner, resulting in mutual slowing down of permeation fluxes. If thermodynamic coupling effects are ignored, significantly higher fluxes are anticipated than those that are experimentally observed.

A deep insight into the polystyrene chain in cyclohexane at theta temperature: molecular dynamics simulation and quantum chemical calculations.

Molecular characteristics of an atactic polystyrene (aPS) chain with different lengths in a theta solvent, cyclohexane at 307.65K, were studied via molecular dynamics (MD) simulation. The interaction energy of the aPS dilute solution models and Flory-Huggins (FH) interaction parameter were calculated to investigate the effect of the chain molecular weight on its compatibility with the solvent molecules. The simulation results illustrated that increasing the chain length increased the interactions between the chain and the solvent molecules. The chain dimensions via calculating the radius of gyration (Rg) and end-to-end distance, <r0>, were measured. Mean square displacement (MSD) and diffusivity coefficient of the chains were calculated to determine their dynamic behavior. The results exhibited that two factors of the chain movability and size were important for the diffusion in oligomeric state. Additionally, viscosity of the resultant dilute solutions was calculated via nonequilibrium molecular dynamics simulation (NEMD). Moreover, the steric hindrance of the chains was determined by radial distribution function (RDF) analysis. The calculated characteristics of the chain and solution viscosity results showed a good agreement with experimental published works. Measurement of the potential field of cyclohexane-cyclohexane and aPS-cyclohexane pairs was also based on their potential field via quantum chemical calculations to determine the special orientation of the solvent molecules to each other and to the polymer segments, respectively. Graphical abstract (a) The equilibrated dilute solution model of polystyrene in cyclohexane at theta temperature (the red and yellow balls represent carbon and hydrogen atoms, respectively. The cyclohexane molecules are illustrated in line style in the box), (b) the electrostatic potential field around an optimized structure containing two cyclohexane molecules, and (c) around the sole cyclohexane molecule and polystyrene with two repeating units (carbon and hydrogen atoms are represented in green and yellow, respectively).

Phase Diagrams of Binary Low Bandgap Conjugated Polymer Solutions and Blends

Liquid–liquid phase diagrams of binary polymer–solvent and fullerene–solvent mixtures were qualitatively predicted by using the Flory–Huggins (FH) lattice theory as a function of solvent, polymer, ...

All-atom molecular dynamics study on the non-solvent induced phase separation: Thermodynamics of adding water to poly(vinylidene fluoride)/N-methyl-2-pyrrolidone solution.

The change in the thermodynamics when adding water in poly(vinylidene fluoride) (PVDF)/N-methyl-2-pyrrolidone (NMP) solution is studied from all atom molecular dynamics (MD) simulations. This is done by estimating the free energy of mixing of PVDF/NMP solution with increasing volume fraction of water (ϕw) using an appropriately chosen thermodynamic cycle and the Bennett acceptance ratio method. The MD calculations predict the thermodynamic phase separation point of water/NMP/PVDF to be at ϕw = 0.08, in close agreement with the experimental cloud point measurement (ϕw = 0.05). Examining the enthalpic and entropic components of the free energy of mixing reveals that at low concentrations of water, the enthalpy term has the most significant contribution to the miscibility of the ternary system, whereas at higher concentrations of water, the entropy term dominates. Finally, the free energy of mixing was compared with the Flory-Huggins (FH) free energy of mixing by computing the concentration-dependent interaction parameters from MD simulations. The FH model inadequately predicted the miscibility of the PVDF solution, mainly due to its negligence of the excess entropy of mixing.

Effects of molecular complexation on phase equilibria in mixtures of urea/polyethylene glycol derivatives and electrochemical performance of urethane based polymer electrolyte membranes for solid-state lithium ion battery

Phase diagram approach has been extended to the determination of phase diagram of a binary pair of urea with polyethylene glycol (PEG) in order to providence guidance to the formulation window of isotropic polymer electrolyte membranes (PEMs) with emphasis on the electrochemical performance. Effect of molecular weight of PEG on solid-liquid phase diagrams of its mixtures with urea has been demonstrated experimentally and theoretically. The observed change of eutectic, immiscibility loop, azeotrope type phase diagrams with increasing PEG molecular weight (or decreasing chain-ends) has been analyzed in the context of the combined Flory-Huggins (FH) theory of liquid-liquid demixing and phase field (PF) theory of crystal solidification. This rich phase behavior has been captured via the variation of crystalline-crystalline interaction strength of the combined FH-PF free energies. Subsequently, the phase diagram of poly (ethylene glycol) diacrylate (PEGDA)/urea was constructed in the framework of the aforementioned FH-PF theory. The incorporation of urea not only dissociates lithium cation from its salt, but also enhances the ionic conductivity of urea-modified polymer electrolytes dramatically. However, small molecule hydrophilic urea was found to be electrochemically unstable in the charge/discharge cycling test. To alleviate such shortcoming, urea (or urethane) linkage was imparted into the network chains by synthesizing PEG-bis(carbamate dimethacrylate) (PEGBCDMA) and subsequently photopolymerizing in the presence of SCN plasticizer and LiTFSI salt to afford the ion conductive PEM network. The as-synthesized PEGBCDMA based PEM consisting of PEGBCDMA/SCN/LiTFSI (20/40/40 ratio by weight) turned out to be completely amorphous and transparent before and after photo-crosslinking. The incorporation of urethane linkages in the PEM network exhibited enhanced ionic conductivity, improved thermal stability, and superior tensile properties with improved capacity retention during charge/discharge cycling, suggesting potentials for application in solid-state lithium ion battery.

Investigation of the Dependence of the Flory–Huggins Interaction Parameter on Temperature and Composition in a Drug–Polymer System

The Flory-Huggins (F-H) solubility equation has been widely used to describe the solubility of a small-molecule drug in a polymeric carrier and thus determine the design space available for formulating a stable amorphous solid dispersion. The F-H interaction parameter (χ) describes the thermodynamic properties of drug-polymer solutions and accounts for any enthalpic and entropic changes in solubility. Many studies have found that for a limited compositional range, χ varies proportionally to the inverse of the melting temperature of the drug. We explored this relationship using a highly sensitive DSC technique to detect remaining residual crystalline active pharmaceutical ingredients (APIs) following annealing of ball milled mixtures of crystalline itraconazole (ITZ) and either Soluplus or hydroxypropyl methylcellulose phthalate (HPMCP) at temperatures near the estimated solubility curve. Depending on the experimental approach taken, the measurement of drug-polymer solubility can be restricted to mixtures with a high proportion of drug, but in this study, solubility was experimentally determined for mixtures with API content as low as 10 wt %. Results suggest that the proposed linear relationship does not extend to compositions with smaller amounts of API, instead indicating that χ was both temperature- and composition-dependent for the systems studied. The feasibility of this technique to measure interactions in a ternary system containing itraconazole and both polymers was also determined; ITZ-HPMCP exhibited the most favorable values of χ, while ITZ-Soluplus and ITZ-Soluplus-HPMCP demonstrated similar interaction parameters.

Flory-Huggins Based Model to Determine Thermodynamic Property of Polymeric Membrane Solution

Flory-Huggins (F-H) model has been widely used to analyze the thermodynamic behavior of polymeric membrane solution during the formation of membrane structure in a phase inversion process. The F-H model involves concentration and binary interaction parameter of components in membrane solution. Those parameters are used to calculate the composition of membrane solution at equilibrium which is then plotted on ternary diagram known as a binodal curve. The binodal curve is used to determine the type of demixing of the polymeric membrane solution and to predict the structure of resulted membrane. Several modifications of F-H model have been conducted in relation to composition (ternary or quaternary) and temperature of the membrane solution. In this paper, the development of F-H model used in designing polymeric membrane by phase inversion method, particularly immersion precipitation method, will be reviewed. The structure and performance of membranes that are governed by the thermodynamic property of the membrane solution based on F-H model will be discussed.

A novel Nanodiamond based IoNanofluid: Experimental and mathematical study of thermal properties

A novel IoNanofluid consisting of 1-Butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] as ionic liquid and Nanodiamond (ND with 8 nm size) as nanoparticle was produced and characterized. The ND surface was modified by oleic acid in order to enhance its thermal property and stability in the ionic liquid. The ND dispersion with volumetric percentages of 0.36, 0.69 and 1.04 in the ionic liquid led to thermal conductivity enhancement percentages of 4.2, 5.3 and 9.3, respectively compared to that of the base fluid. The corresponding IoNanofluid viscosity enhancement percentages were 32, 67 and 126, respectively. One of the main factors that contributes to the aforementioned thermal conductivity increases in ionic liquid is the long alkyl chains in the cations of [BMIM][BF4]. The Eyring theory coupled with the Flory-Huggins (FH) model was used as a thermodynamic model to predict the viscosity, and the results of the proposed model were in satisfactory agreement with the experimental data. The shape, structure, size and characterization of ND as well as IoNanofluid were investigated by the results of XRD, DSC, FTIR, RAMAN, DLS, TEM and SAXS analyses.

Preparation of pharmaceutical cocrystal formulations via melt mixing technique: A thermodynamic perspective

The aim of the present study was to evaluate the thermodynamic properties of in-situ formation of cocrystal formulations by the melt-mixing method. Specifically, the thermodynamic mixing behaviour of carbamazepine-nicotinamide and ibuprofen-nicotinamide cocrystals prepared with the aid of Soluplus® (SOL) were evaluated using thermodynamic lattice-based solution theories. Thermodynamic miscibility of both cocrystals with SOL was predicted by calculating Gibb′s free energy based on the Flory-Huggins (FH) interaction parameter (χ), while the activity coefficient of cocrystals estimated with the aid of solid–liquid equilibrium equation and FH lattice theory, showed good thermodynamic miscibility of the components at elevated temperatures used normally during melt-mixing based processes. Complete phase transition diagrams constructed with the aid of DSC measurements and FH solution theory, suggested the existence of two transition zones: (1) a stable cocrystal zone, located at the right-hand-side of the spinodal phase separation curve, where stable cocrystals are prepared and (2) an unstable cocrystal zone, located at the left-hand-side of the spinodal curve up to liquidus, where the matrixforming polymer sets a kinetic barrier to recrystallization and hence, a barrier to the formation of cocrystals. The validity of the suggested thermodynamic phase transition zones was experimentally verified by ATR-FTIR and hot-stage polarized light microscopy.

Influence of Hansen solubility parameters on exfoliation of organophilic fluoromica

The influence of different surface energies described by Hansen solubility parameters (HSP) on the exfoliation of organophilic fluoromicas is investigated. HSP values of four synthetic organophilic fluoromica with different surfactants have been predetermined. Those surfactants change the fluoromica surface energies described by HSP. The HSP are used to calculate the dispersibility of the various organophilic fluoromica in chloroform via Flory-Huggins (F-H) theory. The F-H parameter (χ) describes the effective difference in HSP related surface energies of particles and chloroform molecules, which is related to the energy cost of exfoliation. An influence of F-H parameter is detected on the delamination state of organophilic fluoromica. The delamination state is evaluated quantitatively using atomic force microscopy (AFM). In the case of a high F-H parameter (χ > 0.15), aggregated and unstable fluoromica dispersions are obtained. Whereas in the case of F-H parameters near zero, exfoliated and stable fluoromica dispersions are achieved. The presence of surfactant on the surface of exfoliated fluoromica flakes is proven by Fourier-transform infrared spectroscopy (FT-IR), and density functional theory (DFT) calculation.

Predictive construction of phase diagram of ternary solutions containing polymer/solvent/nonsolvent using modified Flory-Huggins model

The Flory-Huggins (FH) model has been one of the most used models in theoretical calculations which has been proved to be sensitive to values assigned as interaction parameters. In this work, a predictive equation is implemented to implicitly couple the concept of compressible regular solution theory of Ruzette and Mayes into the original FH model to obtain a new concertation-dependent interaction parameter equation. Then, the modified model (m-FH) is applied for construction of phase diagram of ternary solutions containing polymer/solvent/nonsolvent where experimental data for ternary systems were collected from the literature. In order to compare and analyze the model performance, the individual absolute relative deviation (IARD (%)) was used. The m-FH model revealed acceptable accuracy in calculations without prior need for correlation to experimental data.

Synthesis and characterization of PMMA and organic modified montmorilonites nanocomposites via in situ polymerization assisted by sonication

Abstract A variety of organo-modified montmorillonite (OMMT) and poly(methylmethacrylate) (PMMA) nanocomposites (CPN) were synthetized by in situ polymerization in a chloroform solution under probe sonication at clay loadings of 3 mass%. A factorial experimental design was used to study the effects of the synthesis variables: Flory-Huggins (F-H) interaction parameters between PMMA and clay organomodifier (three grades of OMMT) and sonication energy (26.0 kJ, 30.3 kJ and 34.6 kJ), aiming clay dispersion at nanoscale levels into the polymeric matrix and improvements in CPN properties. The distinct surfactant side groups of commercial OMMT were: hydroxyl (C30B), aryl (C10A) or alkyl (C25A), considering their similar interlayer space. Multiple techniques of analysis to evaluate the level of clay dispersion were used. Small-amplitude oscillatory shear rheology (SAOS) indicated a high level of clay dispersion for the PMMA/C25A CPN and a tendency to form a percolated network structure from the low shear thinning exponent nω of complex viscosity, either at low (nω = −0.97) or high (nω = −0.83) sonication energy. However, the rheological results showed a low level of clay dispersion for PMMA/C10A (nω = −0.70) and PMMA/C30B (nω = −0.40). The F-H interaction parameter was the statistically significant factor for the shear thinning exponent nω response. X-ray diffraction (XRD) of CPN exhibited no discernible reflections for PMMA/C25A-26 kJ and PMMA/C10A-30.3 kJ CPN, suggesting that a high level of clay dispersion was achieved. Transmission electronic microscopy (TEM) images of PMMA/C25A-36.4 kJ and PMMA/C30B-26 kJ CPN showed exfoliated/intercalated and intercalated morphologies, respectively. Thermogravimetry presented a significant increase in PMMA chain scission temperature of up to 82 °C for all CPN when compared to pristine PMMA. The UV–visible transmittance of PMMA/C25A-26 kJ CPN showed to be around 4.5% lower in comparison with pristine PMMA. The CPN refractive index showed a slight reduction, which could even candidate them for new materials in optical electronic devices. The improvements in the verified properties for PMMA/C25A CPN were attributed to the lower F-H interaction parameter of C25A alkyl surfactant with chloroform when considering the others OMMT side groups. The chemical affinity of the alkyl chain to the chloroform could contribute to the diffusion of the solvent/monomer solution into the interlayer space of the clay, prior to polymerization, and then the polymer chain growth to push the layers apart.

Measurement of Hansen solubility parameters for organophilic fluoromica and evaluation of potential solvents for exfoliation

Abstract A method to measure Hansen solubility parameters for organophilic fluoromica is developed. For this purpose, fluoromica with four different intercalated molecules (surfactants) have been dispersed in various solvents. These surfactants change the fluoromica surface energies described by Hansen solubility parameters (HSP). The three Hansen solubility parameters (dispersion, polar and hydrogen bonding) of different organophilic fluoromicas have been obtained by using gravimetric analysis. The dispersion parameters for all four organophilic fluoromicas are almost identical, with a value around 17 MPa . Whereas polar and H-bonding parameters are varying with the used surfactants. Surprisingly the polar and hydrogen bonding values for hydrophobic alkyl chain tailored surfactants are higher than those for a hydrophilic surfactant with poly(ethylene glycol) chains. The determined HSP values allow calculating the dispersibility of the organophilic fluoromica in solvents via the Flory-Huggins (F-H) parameter. These F-H parameters describes the effective difference in HSP related surface energies of particles and solvent molecules and are used to identify potential solvents for an exfoliation process. With this approach, beside known solvents such as chloroform, also new potential candidates such as trichloroethylene, and benzyl ethyl ether are identified for dispersing/exfoliating modified organophilic fluoromica. This work is accompanied by X-ray diffraction (XRD) measurements to gain knowledge about the interlayer space of the different organophilic fluoromicas.

Impact of Drug-Polymer Miscibility on Enthalpy Relaxation of Irbesartan Amorphous Solid Dispersions.

Drug-polymer miscibility has been proposed to play a critical role in physical stability of amorphous solid dispersions (ASDs). The purpose of the current work was to investigate the role of drug-polymer miscibility on molecular mobility, measured as enthalpy relaxation (ER) of amorphous irbesartan (IBS) in ASDs. Two polymers, i.e. polyvinylpyrrolidone K30 (PVP K30) and hydroxypropyl methylcellulose acetate succinate (HPMCAS), were used to generate ASDs with 10% w/w of the polymer. Drug-polymer miscibility was determined using melting point depression (MPD) method. Molecular mobility was assessed from ER studies at a common degree of undercooling (DOU) (Tg - 13.0°C ± 0.5°C). IBS exhibited higher miscibility in PVP K30 as compared to HPMCAS at temperature > 140°C. However, extrapolation of miscibility data to storage temperature (62°C) using Flory-Huggins (F-H) theory revealed a reversal of the trend. Miscibility of IBS was found to be higher in HPMCAS (2.6%) than PVP K30 (1.3%) at 62°C. Stretched relaxation time (τβ) of 17.4365h and 7.0886h was obtained for IBS-HPMCAS and IBS-PVP K30 ASDs, respectively. Miscibility of drug-polymer at storage temperature explained the behavior of the molecular mobility, while miscibility near the melting point provided a reverse trend. Results suggest that drug-polymer miscibility determined at temperatures higher than the storage temperature should be viewed cautiously.

Fe-Oxide Nanomaterial: Synthesis, Characterization and Lead Removal

Organic solvent free iron oxide nanomaterial used for lead removal was synthesized by co-precipitation method. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopic with energy dispersive X-ray analysis (SEM-EDX), X-ray diffraction (XRD) and thermo gravimetric-differential thermal (TG-DTA) analysis were used to determine the surface characteristics and analysis of iron oxide. Optimization of solution pH, adsorbent dosage, contact time, agitation speed and initial lead ion concentration were conducted for further adsorption isotherm, kinetics, thermodynamics and desorption study. Langmuir sorption isotherm model fits the adsorption data better than Freundlich, Dubinin-Radushkevich (D-RK) and Flory-Huggins (FH) models. The mean adsorption energy and free energy obtained from D-RK and FH models guides that the mechanism was under control of physical adsorption and actuality of spontaneous reaction, respectively. From kinetics of adsorption pseudo second (PSO) model fits well than pseudo first (PFO) and Elovich adsorption-reaction models. And to test whether the reaction is under control of adsorption-diffusion or not the intra particle diffusion (IPD) model was tested, but it fails to pass through the origin. This indicates that the reaction mechanism only under control of adsorption-reaction. The maximum adsorption capacity (qmax) of the adsorbent was 70.422 mg/g.

Prediction of Initial Miscibility for Ternary Polyurethane Reaction Mixtures on Basis of Solubility Parameters and Flory–Huggins Theory

AbstractThe initial miscibility in bi‐soft segment polyurethane reaction mixtures is investigated on the basis of Flory–Huggins (FH) theory and solubility parameters (SPs). Different group contribution theories are applied to estimate the SPs of polyether polyol (PEP) structures and 1,6‐hexamethylene diisocyanate (HDI). The PEP structure comprising starter molecule, ethylene oxide/propylene oxide moieties, and end‐functional hydroxyl groups is considered in the calculations. Binodal curves are determined computationally for binary PEP mixtures as well as for a ternary mixture consisting of HDI and a binary mixture of partially miscible PEPs. The computed phase equilibria are found to be in good agreement to experimental cloud points and binodal compositions. The prediction of miscibility for practically relevant ternary polyurethane systems on the basis of FH theory and SPs is thus feasible. Additionally, the study demonstrates that HDI is acting as a compatibilizer for partially miscible PEPs in the initial reaction mixture.

Measurement and Correlation of Activity, Density, and Speed of Sound for Binary Mixtures of 1-Propanol + Poly(Propylene Glycol) 400, 725, and 1025

The improved isopiestic method was used to measure 1-propanol activity data for several binary mixtures of 1-propanol + poly(propylene glycol) 400 (PPG400)/poly(propylene glycol) 725 (PPG725)/poly(propylene glycol) 1025 (PPG1025) at 298.15 K. The effect of polymer molar mass was studied on the solvent activity and vapor pressure of the studied systems. The results indicate that solvent activity increases with the increasing of the polymer molar mass. These data have been correlated with different activity models including Flory–Huggins (FH), modified Flory–Huggins, NRTL, NRF-NRTL, Wilson, and NRF–Wilson models. The obtained values of standard deviations for the models represent that modified Flory–Huggins model have good agreement with the experimental data. The apparent specific volume, excess specific volume, isentropic compressibility, isentropic compressibility increments, and apparent specific isentropic compressibility quantities were obtained with use of density and speed of sound data in the 1-propanol + poly(propylene glycol) 400/poly(propylene glycol) 725 systems at T = 288.15 to 318.15 K which supplies the strong solute–solvent interactions and more compatibility between 1-propanol with PPG400 rather than the other polymers.

Charge pattern matching as a ‘fuzzy’ mode of molecular recognition for the functional phase separations of intrinsically disordered proteins

Biologically functional liquid–liquid phase separation of intrinsically disordered proteins (IDPs) is driven by interactions encoded by their amino acid sequences. Little is currently known about the molecular recognition mechanisms for distributing different IDP sequences into various cellular membraneless compartments. Pertinent physics was addressed recently by applying random-phase-approximation (RPA) polymer theory to electrostatics, which is a major energetic component governing IDP phase properties. RPA accounts for charge patterns and thus has advantages over Flory–Huggins (FH) and Overbeek–Voorn mean-field theories. To make progress toward deciphering the phase behaviors of multiple IDP sequences, the RPA formulation for one IDP species plus solvent is hereby extended to treat polyampholyte solutions containing two IDP species plus solvent. The new formulation generally allows for binary coexistence of two phases, each containing a different set of volume fractions for the two different IDP sequences. The asymmetry between the two predicted coexisting phases with regard to their ratios for the two sequences increases with increasing mismatch between their charge patterns. This finding points to a multivalent, stochastic, ‘fuzzy’ mode of molecular recognition that helps populate various IDP sequences differentially into separate phase compartments. An intuitive illustration of this trend is provided by FH models, whereby a hypothetical case of ternary coexistence is also explored. Augmentations of the present RPA theory with a relative permittivity that depends on IDP volume fraction lead to higher propensities to phase separate, in line with the case with one IDP species we studied previously. Notably, the cooperative, phase-separation-enhancing effects predicted by the prescriptions for we deem physically plausible are much more prominent than that entailed by common effective medium approximations based on Maxwell Garnett and Bruggeman mixing formulas. Ramifications of our findings on further theoretical development for IDP phase separation are discussed.

A comprehensive molecular dynamics study of a single polystyrene chain in a good solvent

In this study, molecular characteristics of polystyrene (PS) was calculated measuring its dilute-solution properties in toluene at 288.15 K via molecular dynamics (MD) simulations. The solution models consisted of PS chains with different number of repeating units all of which were in a dilute regime. In order to investigate the compatibility between the polymer and the solvent molecules, interaction energy and Flory-Huggins (FH) interaction parameter were estimated. The simulation results indicate that increasing the chain repeating units enhanced the interaction between the solute and the solvent. Additionally, the chain dimensions were evaluated calculating the radius of gyration (Rg) and end-to-end distance, r0. To determine the dynamic behavior of the chains in the solutions, mean square displacement (MSD) and diffusivity coefficient were calculated. The simulation results indicated that the chain rigidity at low molecular weight and chain flexibility with increasing the molecular weight influenced chains dynamic behavior and diffusivity. Moreover, radial distribution function (RDF) illustrated the effect of steric hindrance of the chains in dilute solution on capturing the solvent molecules. In addition, solution viscosity was calculated by performing non-equilibrium molecular dynamics simulation (NEMD). The obtained results of chain characteristics and viscosity showed a good agreement with experimental results published previously. This agreement confirms the accuracy of the applied simulation method to characterize the dilute solutions and the chains characteristics.

Modeling non-electrolyte hydrogel swelling using the adjusted parameters from liquid-liquid equilibrium data of the linear polymer

Hydrogels are tridimensional elastic hydrophilic cross-linked polymers with the ability to absorb water in a process called swelling. The Flory-Huggins (FH) theory can be applied to model hydrogel swelling with appropriate adjustments. In the literature the FH model parameter is directly estimated from experimental data on swelling. The target of this paper is to evaluate the effect of using parameters estimated from liquid-liquid equilibria of the linear polymer directly in the swelling modeling of the respective cross-linked polymer as these data can be easily found in literature. Three methods that use different equations for the FH parameter and two methods for the mechanical contribution are evaluated. These models were applied to the polymer poly(N-isopropylacrylamide), PNIPA, and compared in three swelling intervals: the volume contraction region; the transition temperature; and the region of volume expansion. The most relevant and important behaviors of each region are shown, analyzed and discussed.