聚合物溶液凝聚过程的数学模拟与优化Ⅰ.凝聚过程的相平衡和动力学模型

对聚合物溶液在多釜凝聚过程的聚合物-溶剂-水多相体系的相平衡研究表明,当聚合物浓度为20％—30％(体积)时,可将聚合物溶液近似作为纯溶剂处理;聚合物种类对相平衡基本无影响。以稀土异戊橡胶的凝聚为例,建立了等速凝聚阶段和减速凝聚阶段的动力学模型。     

Flory溶液理论中待定参数的决定

用反相色谱法(IGLC)测定聚合物和溶剂的相互作用参数X,推算出Flory聚合物溶液理论中的交换能参数X_(12),结合本文估算的聚合物和溶剂的接触表面之比S_1/S_2,计算了聚二甲基硅氧烷(PDMS)、天然橡胶(NR)、聚苯乙烯(PS)和聚异丁烯(PIB)等溶液体系中,X和聚合物链节分率φ_2的关系,结果能与实验值很好符合,并且还计算了溶液的体积变化V~(?)/V~(?)和无限稀混合焓△H_(?)~∞.     

用拟二元方法研究iPP-DBP-DPP三元体系的热致相分离热力学

采用拟二元方法研究等规聚丙烯(iPP)-邻苯二甲酸二丁酯(DBP)-邻苯二甲酸二辛酯(DOP)三元聚合物溶液的热致相分离热力学，得出了拟二元相图的数学关联方法．采用光学显微镜法测定浊点温度，采用差式扫描量热法(DSC)测定熔点、动态结晶温度．利用浊点测定数据回归聚合物一共溶剂的交互作用参数X的表达式，X是共溶剂配比和温度的函数，以此为基础计算的拟二元相图与实验数据吻合较好．发现共溶剂中DBP份数增加，相分离类型由单纯固液分相形式转变为液液分相、固液分相依次发生形式，共溶剂配比能调控拟二元相图结构．研究表明，只需测定一个较低冷却速率下几种共溶剂配比的拟二元溶液的浊点温度、分别测定几个冷却速率下iPP-DOP二元溶液的动态结晶温度即可掌握该三元溶液热致相分离热力学的全部信息．其可用来指导制膜过程，并能准确预测形成的膜结构形貌．     

气体在混合溶液中溶解度的分子热力学计算

开发出一个分子热力学模型来预测低压下难溶于溶剂且不与溶剂发生反应的气体在二元混合溶液的溶解度,混合物中含有缔合作用成分及溶剂化作用成分,即形成配位化合物。在该模型中,Gibbs能为三个等温混合过程的和。溶质的偏摩尔过量Gibbs能由两部分组成,即化学和物理贡献。为了验证该模型的准确性,将该模型用于计算氮气在丙酮和氯仿混合物的溶解度。考虑实验的不确定度,氮气在二元混合溶液中的溶解度与实验数据吻合良好。     

涂料干燥过程中溶剂扩散系数的预测与测试方法

基于改进的自由体积模型,计算了不同温度下和溶剂质量分数的聚甲基丙烯酸甲酯(PMMA)?丙酮体系中溶剂的扩散系数,并通过称重法和热重分析法进行验证.结果表明,溶剂扩散系数的预测值与称重法的测试值吻合程度较高,证明改进的自由体积模型可以较好地预测涂料中溶剂的扩散系数.     

粒子在溶液中吸附聚电解质行为及粒子间的相互作用(Ⅰ)模型建立

以自洽场 (CSF)理论为基础 ,综合粒子、溶剂分子和聚合物链节之间的相互作用及聚合物分子链电荷的作用对粒子在溶液中吸附聚合物的影响 ,采用前末端链节决定随机行走模型 (PRDWM)建立了粒子在聚合物溶液中吸附平衡后的粒子表面的链节密度分布的数学模型———链节密度分布函数 ,并通过吸附前后粒子表面自由能的变化建立了吸附聚合物分子链的粒子间的相互作用势能模型     

残留溶剂在PMMA-CA聚合物膜中迁移及影响的多尺度分析

杂质对功能高分子聚合物理化性质的影响具有重要的学术价值与应用意义。今分别通过分子动力学(Molecular Dynamics,MD)及密度泛函(Density Functional Theory,DFT)等方法探索了聚合物玻璃态和橡胶态下溶剂扩散系数的不同以及残留溶剂对聚合物分子解离能的影响。根据自由体积理论,对聚甲基丙烯酸甲酯-丙烯酰胺杯芳烃(PMMA-CA)的玻璃化温度进行了分子动力学(MD)模拟,得到的自由体积与温度的关系曲线显示其玻璃化温度为395K。考察了玻璃态和橡胶态下溶剂扩散系数的不同,MD模拟得到的均方位移(Mean Square Displacement,MSD)曲线显示,聚合物在玻璃态下溶剂的自扩散系数远低于橡胶态下。通过密度泛函方法计算残留溶剂分子对杯芳烃解离能的影响,结果表明膜制备过程中残留的溶剂分子有利于杯芳烃的解离,但其影响比MMA分子共聚要弱得多。     

α-蒎烯-蒎烷-长叶烯体系汽液平衡及其过量Gibbs自由能与超额焓

采用改进Ellis平衡釜测定了α-蒎烯-蒎烷、α-蒎烯-长叶烯、蒎烷-长叶烯三个二元体系及α-蒎烯-蒎烷-长叶烯三元体系常压汽液平衡数据,经Herington规则检验符合热力学一致性。由汽液平衡数据求出每个二元体系中各组分的活度系数,再关联得到相应的过量Gibbs自由能与超额焓实验值。结果表明,α-蒎烯-蒎烷体系的Gibbs自由能对理想溶液呈现较小的正偏差,而α-蒎烯―长叶烯和蒎烷-长叶烯体系Gibbs自由能对理想溶液呈现负偏差。根据Wilson方程对三个二元体系的过量Gibbs自由能和超额焓进行了计算,关联值与实验值吻合,对α-蒎烯-蒎烷体系最大超额焓为120.48 J×mol~(-1),α-蒎烯―长叶烯体系最大超额焓为401.09 J×mol~(-1),蒎烷-长叶烯体系最大超额焓为685.75J×mol~(-1)。由关联得到的二元体系能量参数推算了α-蒎烯-蒎烷—长叶烯三元体系的过量Gibbs自由能和超额焓,过量Gibbs自由能的实验值与计算值基本吻合,平均相对偏差为1.7147%,该三元体系的最大超额焓为627.16 J×mol~(-1)。     

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.     

LiNO_3-KNO_3二元相图的热力学优化和计算

引入短程有序—扩展似化学模型来描述Li NO3-KNO3二元体系液相的Gibbs自由能,根据实验测定的相图数据,运用CALPHAD(Calculation of Phase Diagram)技术对该体系进行了热力学优化和计算,优化计算的结果和实测值符合很好。     

Application of the UNIFAC-FV group contribution method to the prediction of relative compatibility of plasticizers with PVC

The applicability of a modified version of UNIFAC group contribution method, UNIFAC-FV, is explored for use in predicting liquid-liquid equilibrium behavior of plasticizer/PVC systems. A Fortran program for the UNIFAC-FV model has been written to calculate the activities and changes in the Gibbs free energy for multicomponent systems. By this means, the interaction parameter X for a polymer-solvent system is defined using the well known Flory-Huggins equation. The concentration dependent Gibbs free energy of mixing is used as a criterion for the relative compatibility of the PVC-plasticizer system. The method indicates that, for the plasticizers examined, DOS is the least compatible and DBP is the most compatible with PVC. This confirms the results of the glass transition width measured by dynamic mechanical analysis previously reported.     

Sorption and diffusion measurements in ternary polymer-solvent-solvent systems by means of a magnetic suspension balance—Experimental methods and correlations with a modified Flory-Huggins and free-volume theory

Diffusion and sorption data of methanol and toluene in the ternary system methanol-toluene-poly(vinylacetate) (pvac) were measured by means of a magnetic suspension balance (MSB). Ternary diffusion coefficients were determined from sorption kinetics with a method of Crank [1975. The Mathematics of Diffusion, second ed. Claredon Press, Oxford] classically used for binary polymer solvent systems. Assumptions and limitations for this method are discussed. Sorption data of methanol and toluene in the ternary system were correlated with a modified Flory-Huggins theory taking four instead of three interaction parameters into account and compared with predictions of UNIFAC-FV. All four binary Flory-Huggins interaction parameters were correlated as a function of concentration, determined from binary polymer-solvent sorption measurements and from solvent-solvent equilibrium data. The modified Flory-Huggins approach for ternary systems predicts the two limiting cases for the binary polymer-solvent as well the two solvent-solvent equilibria. Diffusion coefficients determined from sorption kinetics measurements were correlated with free-volume theory predictions of Vrentas et al. [1984. Self diffusion in polymer-solvent-solvent systems. Journal of Polymer Science, Polymer Physics Edition, 22, 459-469] and compared with a few available literature data from Surana et al. [1998. Diffusion and equilibrium measurements in ternary polymer-solvent-solvent systems using inverse gas chromatography. Industrial and Engineering Chemistry Research, 37, 3203-3207]. Cross diffusion terms are not taken into account. Diffusion and sorption data, determined with this gravimetric method, were used in model simulations with modified Flory-Huggins and free-volume theory to predict drying curves of ternary methanol-toluene-pvac solutions. The results were compared with previously published experimental results performed by means of Inverse-Micro-Raman-Spectroscopy (IMRS) from Schabel [2004. Trocknung von Polymerfilmen - Messung von Konzentrationsprofilen mit der Inversen-Mikro-Raman-Spektroskopie. Ph.D. Thesis, Universität Karlsruhe (TH), Germany].     

A modified segment-based nonrandom two-liquid model for the calculation of vapor-liquid equilibrium of aqueous polymer-salt solutions

A new model for representation of the excess Gibbs energy of polymer-electrolyte solutions is proposed. The excess Gibbs energy of a polymer-electrolyte solution is expressed as a sum of contributions of a combinatorial, a long-range and a short-range excess Gibbs energy term. The Flory-Huggins expression and the Pitzer's extension of Debye-Hückel function are used, respectively, as a combinatorial and a long-range contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the modified nonrandom two-liquid (NRTL) model, is developed to account for the short-range contribution to the excess Gibbs energy. The model provides a versatile and flexible thermodynamic framework for both correlating and predicting the phase equilibrium of electrolyte solutions, polymer solutions and complex systems containing both electrolytes and polymers. The utility of the model is demonstrated with successful representation of vapor-liquid equilibrium of several PEG or PPG-salt-H₂O systems at different polymer molar masses. Results are compared with those obtained from the NRTL model.     

New local composition model for polymer solutions

A new segment-based local composition model is presented for the excess Gibbs energy of polymer solutions. The excess Gibbs energy of a polymer solution is expressed as a sum of contributions of a combinatorial and a residual excess Gibbs energy term. The truncated Freed correction to Flory-Huggins expression as first correction for the configurational entropy of mixing is used as a combinatorial contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the NRF-Wilson model, is developed to account for the contribution of the residual excess Gibbs energy. The main difference between this model and the segment-based NRTL model available in the literature is in the nature of the short-range energy parameter and their references states. The utility of the model is demonstrated with the successful representation of the vapor-liquid equilibria, density and viscosity of several polymer solutions. The results show that, the model is valid for the whole range of polymer concentration, from dilute solution up to saturation. The results are compared with those obtained from the segment-based NRTL and segment-based Wilson models. The model presented in this work produces better results.     

Finitely concentrated partial molar excess properties of solvent/polymer [poly(4-methylstyrene) (PMS), poly(vinylbenzyl chloride) (PVBC)] systems

The finitely concentrated activity coefficients and partial molar excess properties of solvents were measured with inverse gas chromatography (IGC) in polymer solutions containing a poly(4-methylstyrene) (PMS) or a poly(vinylbenzyl chloride) (PVBC). The experimental temperature ranges were 373.15 K to 413.15 K for PMS and 353.15 K to 393.15 K for PVBC. They were over melting point or glass transition temperature of each polymer. Ten kinds of solvents (Acetone, n-Heptane, Cyclohexane, Chloroform, Methylisobutylketone, Trichlorobenzene, Benzene, Toluene, Ethylbenzene, Chlorobenzene) that are important in the chemical engineering field were arbitrarily chosen for binary polymer solutions. The external degree of freedom of original UNIFAC-FV model was empirically modified to give flexibility to itself as a C₁=A+BT from the experimental data in finite concentration. The UNIFAC-FV model included a new external degree of freedom as a function of temperature. The parameters (A, B) were estimated by correlating the activities of solvent with the modified model and extended to predict the partial molar excess properties of solvents in the finite-concentrated polymer solutions. The predicted values were compared with them by original UNIFAC-FV as well as the experimental data. The results obtained with the revised model using the new parameter showed the higher quality than the results obtained by original model.     

A modified entropic expression for the analysis of swelling behavior of polymeric membranes in solutions

The linear mixed relation for mixed molar volume and free-volume were modified to derive our new activity expression attributed to the combined combinatorial and free volume contributions. The validity and applicability of this expression were demonstrated by calculating the solvent activity in polymer solutions and analyzing the swelling behaviors for polymeric membranes. The average absolute deviation (AAD) of these calculated results from the experimental values of solvent activities for polymer solutions was employed for comparison. It is shown that the modified model can yield better results than the original one for most of the systems considered. The swelling behavior of poly vinyl alcohol (PVA) membranes in water/glycol (EG) mixture over a wide range of concentrations was analyzed. The activity of solvents in the liquid and the membrane was calculated by the UNIQUAC model and this present modified model, respectively. The estimations are consistent with experimental data roughly at temperatures of 333 and 343 K. It is found that the modified model is a suitable alternative to the Flory-Huggins equation for the analysis of the swelling behaviors of polymeric membranes in solutions.     

VAPOR-LIQUID EQUILIBRIA OF POLYMER SOLUTION USING UNIQUAC

The UNIQUAC excess Gibbs energy model of Abrams and Prausnitz(1975)is extended to represent thevapor-liquid equilibria of polymer solution with only two adjustable parameters.Discussions on the application ofthe Staverman-Guggenheim and the Flory-Huggins combinatorial contribution in the UNIQUAC model are givenin this paper.The UNIQUAC model with either Staverman-Guggenheim or Flory-Huggins combinatorial expres-sion presents results with about the same accuracy for polymer solutions.Comparisons between the UNIQUAC model and the Flory equation show that theUNIQUAC model can give some better results than the Flory equa-tion in general.