Partition coefficients and the free energy of confinement from simulations of nonideal polymer systems
Partition coefficients and the free energy of confinement from simulations of nonideal polymer systems
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DOI：
10.1021/ma000964a
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发表时间：
2001-01-30
期刊：
影响因子：
5.5
通讯作者：
Bleha, T
中科院分区：
文献类型：
--
作者：
Cifra, P;Bleha, T
报道了通过蒙特卡罗 (MC) 模拟研究实际聚合物体系中的分配平衡。与理想的链处理相比，计算中考虑了诸如真实链中的柔韧性和排除体积、大分子phi的有限浓度以及吸引力强度ε（w）的孔壁上的聚合物吸附等因素。通过模拟估算了非理想条件下狭缝结构中由于链限制而导致的自由能变化 DeltaA/kT。计算了与静态分配和尺寸排阻色谱 (SEC) 相关的分配系数 K 对 lambda、溶质与孔径之比的依赖性。在所有情况下，所考虑的因素都会增强给定 lambda 的分配系数 K，并导致 K 随 lambda 的变化更加渐变；即，非理想分配的分辨率相对于理想链分配的情况降低。发现浓度对空间分配系数 K 的影响明显取决于稀溶液中的溶剂质量。在空间排斥和吸附相结合的混合模式分配中，函数 K(lambda,epsilon (w)) 通过模拟数据的拟合来计算。该函数正确地再现了非理想链的所有液相色谱方案，包括临界色谱。讨论了非理想分配中自由能变化 DeltaA/kT 的解释，该解释基于线圈在其限制下的构象和取向熵的损失。
The investigation of the partitioning equilibrium in real polymer systems by Monte Carlo (MC) simulations is reported. In contrast to ideal chain treatments the factors such as flexibility and excluded volume in real chains, the finite concentration of macromolecules phi, and polymer adsorption on pore walls of the attractive strength epsilon (w) are considered in computations. The free energy change DeltaA/kT due to chain confinement in slitlike structures under nonideal conditions is estimated from simulations. The dependencies of the partition coefficient K on lambda, the solute to pore size ratio, relevant to the static partitioning and to size exclusion chromatography (SEC), were computed. In all cases the factors considered enhance the partition coefficient K for a given lambda and lead to more gradual changes of K with lambda; i.e., the resolving power of the nonideal partitioning decreases relative to a case of ideal chain partitioning. The concentration effect on the steric partitioning coefficient K was found to depend markedly on the solvent quality in dilute solutions. In mixed-mode partitioning by a combination of steric exclusion and adsorption, the function K(lambda,epsilon (w)) is computed by a fit of the simulation data. This function properly reproduces for nonideal chains all liquid chromatography regimes, including the critical chromatography. An interpreta tion of the free energy changes DeltaA/kT in nonideal partitioning, based on the loss of conformational and orientational entropies of coils on their confinement, is discussed.