聚合物-溶剂体系中溶剂的活度模型

引言 GE模型与溶液的活度因子等紧密相联,在计算流体相平衡中具有重要地位.经过以van Laar、Margules方程与Wilson、NRTL关联式以及UNIQUAC和UNIFAC模型为代表的三个阶段的发展,预测准确度已达到实验误差范围,能较好地关联多组分体系的汽液平衡,在电解质溶液、高分子溶液及高度非理想体系中结果亦较满意.     

Upper critical solution temperature-type thermosensitive hydrogel phase equilibrium of poly(2-hydroxyethyl methacrylate)/water/n-alkanol mixtures

We investigated the swelling behavior of upper critical solution temperature (UCST)-type nano-sized poly(2-hydroxyethylmethacrylate) (PHEMA) particle gel with n-propanol and n-butanol in the presence of water. Because PHEMA is a biocompatible hydrogel and is highly water absorptive, it is worthwhile to investigate the phase behavior between PHEMA and water. The swelling behavior of the cross-linked PHEMA particle gel and the phase miscibility of the linear PHEMA mixed with the n-alkanol/water solution were evaluated. Our experimental results showed that increasing the water fraction in the mixed solvent gradually reduces the swelling temperature. Moreover, the two phase region of the PHEMA/water/n-butanol mixture showed sudden expansion at ∼15 vol% water in the ternary diagram. In these systems, oriented interactions among each component exist, which strongly affect the chemical association. The modified double lattice (MDL) and Flory-Huggins (FH) models were employed to describe the swelling and phase behaviors of the given ternary systems. The MDL model matched our data much better than the FH model because it was able to correctly represent the oriented interactions from hydrogen bonding or other specific forces encountered in the systems. To demonstrate the model compatibility to UCST-type swelling behavior, we also examined other polymer solutions. Polyvinyl acetate (PVAc) gel/2-propanol was studied as an associating system and polystyrene (PS)/cyclohexane was evaluated as a non-associating system.     

用状态方程改进的高聚物中溶剂扩散系数预测模型

将Simha-Somcynsky状态方程引入Vrentas-Duda自由体积理论模型,提出改进的高聚物-溶剂体系扩散系数模型,计算常压下橡胶态高聚物中有机溶剂扩散系数对浓度和温度的依存关系.利用高聚物结构单元的范德华体积导出高聚物自由体积分数表达式,通过Simha-Somcynsky方程求取高聚物体积以及对溶剂分子扩散有效的自由体积,避免原模型中繁琐的高聚物粘弹性实验测定和回归高聚物自由体积参数,提高了自由体积理论的预测能力.使用改进的模型预测了苯、甲苯、乙苯和三氯甲烷在聚苯乙烯、聚异丁烯和聚醋酸乙烯酯中的自扩散系数和互扩散系数,计算结果表明改进的自由体积模型具有较高的预测精度.     

A novel transport model for sorption and desorption of penetrants in dense polymeric membranes

The transport of penetrants in polymeric membranes is assumed to be a process of mixing of penetrant and polymer molecules, in which a creep strain is induced concurrently. Based on the assumption and combined with the mass conservation equation and phenomenological diffusive flux expression, a new transport model of penetrant in polymeric membrane is established, in which the total change of excess Gibbs free energy is considered as a sum of three parts calculated by the modified Scatchard-Hildebrand model, Flory-Huggins theory and linear viscoelastic theory, respectively. The partial difference equations in the model are solved by implicit finite difference method of Crank-Nicolson form, and the model parameters are optimized by simplex algorithm. The model is used to calculate various diffusions (Fickian diffusion, and non-Fickian diffusion) of ethanol in polyphthalazine ether sulfone (PPES), and polyphthalazine ether sulfone ketone (PPESK) membranes at 293.15, 298.15, and 303.15 K. The calculated results are in agreement with the experimental data and the maximal relative deviation is no more than 10.54% and the average relative deviation is 4.35%.     

平均球近似法计算电解质活度系数的研究(Ⅱ)——混合电解质水溶液

用(I)报中所得到的阳离子有效直径参数,用平均球近似(MSA)法,在不用混合参数的条件下,预测了32个混合电解质水溶液的离子平均活度系教.预测的Inγ_± 与实验值的平均标准偏差为0.0113.文中还用Pitzer方程作了计算.结果表明本文预测结果比无混合参数的Pitzer方程好得多,接近于带混合参数的Pitzer方程的关联结果,作者还分别预测了各温度下4个混合电解质水溶液饱和浓度时的活度系数,结果令人满意.     

Phase equilibria and surface tension in castor oil-based polyols-water–methanol mixture: Thermodynamic basis

Considering the current environmental issues with petro-polymers, castor oil is a promising green alternative to the polyols to be used as the main raw material for polyurethane. However, the basic information regarding the processability of castor oil-based polyol (CP) such as its miscibility in different solvents is still elusive. Herein we have investigated the phase equilibria and surface tension of various CP solutions using thermo-optical analysis and pendent drop method, respectively. The modified double lattice (MDL) model was employed to theoretically describe those phase equilibria and surface behaviors. The phase diagrams of CPs/methanol binary systems represent upper critical solution temperature (UCST) behaviors, and CPs/methanol/water ternary systems show Treybal Type 2 behaviors. The surface tension results exhibit preferential solvent adsorption, which means affinity of the solvent to be present in surface is higher than that of the polymer. The calculated results showed good agreement with the experimental observations.     

Correlation for volume phase transition of polymeric gel (vinyl alcohol-sodium acrylate copolymer) in alcohol-water solutions

A thermodynamic model was proposed to correlate the phase behavior of a swelling polymeric gel (vinyl alcohol-sodium acrylate copolymer) and the volume phase transition in alcohol (methanol, ethanol or propanol)-water solutions. The model is based on the Flory-Huggins formula for polymer solution coupled with the osmotic pressure by rubber elasticity proposed by Flory. The volume change behavior and the equilibrium concentrations inside and outside the gel were successfully correlated using the present model.     

Estimation of solvent diffusion coefficient in amorphous polymers using the Sanchez-Lacombe equation-of-state

A modified free-volume model was proposed to predict the solvent diffusion coefficient in rubbery polymers without knowledge of any diffusion data. With the introduction of the Sanchez-Lacombe (SL) equation-of-state (EOS) into the Vrentas-Duda model, this model is an attempt to bridge the gap between the thermodynamic and transport properties of polymer solutions. The free volume provided by polymers for solvent diffusion can be estimated solely using the parameters of the SL EOS characteristics and the polymer glass transition temperature; thus the proposed model avoids the need to use polymer viscoelastic data in determination of polymer free-volume parameters. The other parameters in the Vrentas-Duda model remain applicable. Calculated results of solvent self- and mutual-diffusion coefficients of four common solvents in two polymers indicated that the modified model can give reliable predictions. In addition, it can reflect the effect of pressure on solvent diffusivity for concentrated polymer solutions.     

A Molecular Thermodynamic Model for Restricted Swelling Behaviors of Thermo-sensitive Hydrogel

A molecular thermodynamic model was developed for describing the restricted swelling behavior of a thermo-sensitive hydrogel confined in a limited space. The Gibbs free energy includes two contributions, the contribution of mixing of polymer and solvent calculated by using the lattice model of random polymer solution, and the contribution due to the elasticity of polymer network. This model can accurately describe the swelling behavior of restricted hydrogels under uniaxial and biaxial constraints by using two model parameters. One is the interaction energy parameter between polymer network and solvent, and the other is the size parameter depending on the degree of cross-linking. The calculated results show that the swelling ratio reduces significantly and the phase transition temperature decreases slightly as the restricted degree increases, which agree well with the experimental data.     

Influence of the environment on swelling of hydrophilic polymers

The influence of water activity on swelling of cross-linked hydrophilic polymers in electrolyte solutions of various concentrations was studied. A heterophase model was proposed to explain the polymer swelling. It was shown that the change in polymer swelling deals with different water sorption, and is described by water vapour sorption isotherm. At the same time, the volume of external solution taken up by polymer at swelling is constant and independent of concentration of the solution. Three models describing the structure of polymer gels were suggested and discussed on the base of the obtained results.     

Excess volume of polymer/solvent mixtures and proposed model for prediction of activity of solvents based on excess volume data

Density measurements were used to evaluate the excess volume of binary mixtures of poly(ethylene glycol) in water and ethanol solvents, poly(propylene glycol) in water and ethanol solvents, and poly(vinyl alcohol) in water solvent at different temperatures for various molecular weights of polymers. The excess volumes were correlated and expressed by a polynomial in terms of the weight fraction of the polymer. The activity of the solvent was expressed in terms of three parts: excess internal energy, excess entropy, and excess volume. The excess volume was derived from the expression obtained in this work, the excess entropy was derived from Flory's lattice model, and the excess internal energy was used as a weight average of the excess volume and entropy parts. The results indicated good agreement between the activity of the solvent calculated by the proposed model and the experimental data. The proposed model has the advantage that using only simple density measurements the activity values that are necessary in the calculation of thermodynamic properties can be evaluated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1219–1227, 2005     

Swelling and deswelling transition of water-soluble poly(N-isopropylacrylamide) by a method of blob rescaling

The transition behavior of swelling and deswelling of water-soluble poly(N-isopropylacrylamide) was calculated by adecorated UNIQUAC model with blob concept. The deswelling behavior of hydrogels at high temperatures was also reported with shrinking volumes during the transition. Polymer chains were scaled within a directly interacting size as blobs, which are composed of a segmentalized polymer chain and solvent molecules and counted blobs of hypothetical components or segments. The interaction parameters of bulks, UNIQUAC interaction parameters, were approximated with temperature-independent site interaction energies following the blob renormalization transformation. The swelling gel transition volume at each given temperature was calculated with the decorated UNIQUAC model. The blob rescaling model successfully described the first order transition of swelling-deswelling behaviors. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

Thermodynamic properties of polymer solutions: effect of free volume fraction of solvent molecules

Knowledge about the thermodynamic properties of a polymer solution is essential to its applications. These properties are derived on the basis of a statistical mechanics approach by modifying the classic Flory–Huggins theory in this study. The analytical result derived is fitted to the available experimental data such as toluene–polystyrene and benzene–silicone polymer solutions in the literature, and its performance is satisfactory. We show that the inconsistency between the Flory–Huggins theory and experimental observations for many polymer solutions might arise from the negligence of the effects of the free volume fractions of solvent and polymer and the change in the disorientation entropy of polymer molecules.     

Extraordinary swelling behavior of poly(AMPS) organogel in solvent/DMSO binary mixed media

The present article deals with super‐swelling behavior of crosslinked homopolymer of 2‐acrylamido‐2‐methylpropane sulfonic acid, poly(AMPS), in binary mixtures of dimethyl sulfoxide (DMSO) and various polar solvents including water, mono‐, and polyhydric alcohols, and amide solvents such as N‐methyl pyrrolidone. Extraordinary phase transition sequences including a new unusual swelling phenomenon, referred to as “overentrant” swelling, was observed for this polymeric organogel in the solvent/DMSO mixtures. The swelling behaviors were preliminarily explained based on the major interactions involved in the solvation process and dielectric constant of the swelling media. It was established that the “overentrant” region of the swelling profiles was progressed with the increase of dielectric constant of the mixed solvent media. The overentrant region was disappeared with partial replacement of AMPS units with acrylic acid. This was taken as an additional practical evidence for a major role of the sulfonic acid as the main interactive group involved in the solvation process. The unusual phase transitions were also explained via a semiquantitative approach based on the Gutmann's acceptor number and donor number values to emphasis on the key effect of dissociation degree of the sulfonic acid group (as a function of the solvent type and composition) on the swelling behaviors. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Swelling behavior of submicron gel particles

We prepared submicron Poly(N-isopropylacrylamide) gel particles. Their swelling behavior was investigated by a photon correlation spectroscopy (PCS) technique. The swelling behavior of submicron gel particles showed a continuous volume phase transition for various temperatures. We combined the extended Flory-Huggins model for mixing solvent and network with a modified Flory-Rehner theory for the elastic contribution. The proposed model agreed very well with swelling behaviors of both submicron gel particles and bulk gels. A continuous volume phase transition behavior of submicron gel particles was predicted successfully by the proposed model. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 109–114, 1998     

MBr(M=Na,K)在离子液体[Bmim]Br水溶液中的溶解度

为探索溴化1-丁基-3-甲基咪唑([Bmim]Br)离子液体对无机溴化物MBr(M=Na,K)在水中溶解度的影响,采用等温溶解平衡法在常压下测定了298.15~328.15 K范围内MBr在[Bmim]Br(1)+H₂O(2)溶液中的溶解度,考察了离子液体含量对溶解度的影响。实验结果表明,[Bmim]Br的加入会显著降低MBr(M=Na,K)在水中的溶解度,离子液体[Bmim]Br对KBr的盐析作用比对NaBr的盐析作用大。不同温度下的溶解度数据可用Pitzer混合电解质溶液模型进行关联,得到了混合离子相互作用参数以及MBr在混合溶剂中的平均活度因子和溶剂的渗透系数。模型计算的溶解度与实验结果吻合良好,平均活度因子和溶剂的渗透系数均随离子液体含量的增加而增加。     

The effects of interaction energy on the volume phase transition of N-isopropylacrylamide-co-N-isopropylmethacrylamide nano-sized gel particles: Applicability of molecular simulation technique

We investigated the volume phase transition temperatures of N-isopropylmethacrylamide (NIPMA)-co-N-isopropylacrylamide (NIPA) gels with various mole ratios. Nanometer-sized NIPA-co-NIPMA gel particles were prepared by precipitation polymerization and their swelling behaviors were measured using photon correlation spectroscopy (PCS). After applying the interaction energies found using the molecular simulation technique, we predicted the swelling equilibria for the hydrogels in a water system. For studying cross-linked hydrogel particles in water, we have combined the modified double-lattice theory with Flory and Erman's theory of elasticity. To correct for the deviation of the volume transition temperature, we considered the additional energy parameter (?_h) between the cross-linker and solvent molecules. We used the corrected model to describe the swelling behavior of the hydrogel and the volume transition temperature. The corrected model was agreed well with their experimental data with no fitting parameters.     

A model to predict the solubility and permeability of gaseous penetrant in the glassy polymeric membrane at high pressure

In this work, the transport properties of gaseous penetrant through several dense glassy polymeric membranes are studied. The nonequilibrium lattice fluid (NELF) in conjunction with the modified Fick's law and dual mode sorption model was used to simulate the gas transport in glassy polymeric membranes. The approach is based on the sorption, diffusion, in which solubility is calculated based on the NELF model, and diffusion coefficient is obtained from the product thermodynamic coefficient and molecular mobility. The governing equation is solved by the finite element method using COMSOL multi-physics software. The developed model for gas permeability of glassy polymeric membrane can be applied in a wide range of pressure and temperature. The comparison of the calculated permeability and solubility of gasses with the experimental data represented the ability of the developed model. Increasing feed gas temperature increases the gas permeability, while this variation leads to lower gas solubility in the glassy polymeric membranes. The effect of feed temperature and pressure on permeability and solubility is investigated, and the experimental data from literature are described by the developed model. A good prediction of the experimental data can be observed over the considered condition.     

Effect of degree of cross-linking on swelling and on drug release of low viscous chitosan/poly(vinyl alcohol) hydrogels

In the present work, a series of cross-linked LVCS/PVA hydrogels with various feed compositions were prepared using glutaraldehyde as cross-linking agent. The prepared hydrogels were used for dynamic and equilibrium swelling studies. The swelling behavior of these hydrogels was investigated as functions of effect of pH, polymeric compositions and degree of cross-linking. Swelling studies were performed in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing PVA contents in the structure of hydrogels in solutions of higher pH values. This is due to the presence of more hydroxyl groups (–OH) in the PVA structure. On the other hand, by increasing LVCS contents, swelling increased in a solution of acidic pH and it is due to ionization of amino groups (–NH₂), but this swelling was not significant. Swelling of hydrogels was decreased with increase in cross-linking ratio due to tighter hydrogel structure. Porosity and sol–gel fraction were also investigated. It was found that with increase in LVCS and PVA contents porosity and gel fraction increased, whereas by increasing glutaraldehyde content gel fraction increased and porosity decreased. Diffusion coefficient (D) and network parameters, i.e., the average molecular weight between cross-links (M _C), solvent interaction parameters (χ), polymer volume fraction in swollen state (V _2S) and cross-linked density (q) were calculated using Flory–Rehner theory. Selected samples were loaded with model drug diphenhydramine HCl. The release of diphenhydramine HCl was studied for 12 h period in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5 and 7.5. It was observed that drug release increased with increasing PVA contents in the hydrogels, while release of drug decreased as the ratio of cross-linking agent increased in the hydrogel structure owing to strong physical entanglements between polymers. The release mechanisms were studied by fitting experimental data to model equations like zero order, first order, Higuchi and Peppas. Results showed that the kinetics of drug release from hydrogels in buffer solutions of pH 1.2, 5.5 and 7.5 was mainly non-fickian diffusion. Hydrogels were characterized by Fourier transform infrared and X-ray diffraction to confirm the structure and study the crystallinity of hydrogel, respectively.