物理化学学报 >> 2010, Vol. 26 >> Issue (06): 1629-1636.doi: 10.3866/PKU.WHXB20100601

量子化学及计算化学 上一篇    下一篇

平行壁面间平衡聚合物吸附行为的自洽场分析

孙喆, 岳新荣, 刘川, 章爱   

  1. 天津理工大学化学化工学院, 天津 300384
  • 收稿日期:2009-12-09 修回日期:2010-03-13 发布日期:2010-05-28
  • 通讯作者: 孙喆 E-mail:zhesun@tjut.edu.cn

Self Consistent Field Analysis on the Adsorption of Equilibrium Polymers between Two Parallel Plates

SUN Zhe, YUE Xin-Rong, LIU Chuan, ZHANG Ai   

  1. School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, P. R. China
  • Received:2009-12-09 Revised:2010-03-13 Published:2010-05-28
  • Contact: SUN Zhe E-mail:zhesun@tjut.edu.cn

摘要:

采用自洽场理论研究了平衡聚合物在平行壁面间的吸附规律. 结果表明, 平衡聚合物的吸附行为可根据壁面吸附强度划分为弱吸附和强吸附两个区间. 在强吸附区间, 平衡聚合物可以形成明确的吸附层, 增大吸附强度能够引起平均分子链长的陡增, 但不会改变链长分布的指数形式. 平衡聚合物的长链分子在强吸附条件下较短链分子更靠近吸附壁面, 在弱吸附条件下, 则更接近体系中心. 通过计算壁面压强发现: 在弱吸附作用下, 吸附壁面始终受到分子链的推斥作用; 在强吸附作用下, 分子链对壁面的作用随壁面间距的加大由推斥转变为吸引. 平衡聚合物的溶解性和排空效应以及壁面吸附作用之间存在竞争关系,加大排除体积作用参数会引起分子链密度分布的均一化和壁面承受压强的降低.

关键词: 吸附, 平衡聚合物, 自洽场理论, 密度分布, 缔合, 排空效应

Abstract:

Self-consistent field theory is proposed to investigate equilibrium polymers adsorbed between two parallel plates. According to numerical results, the adsorption behavior of the equilibrium polymers can be classified into two regimes, viz. weak adsorption and strong adsorption. For strong adsorption, the apparent adsorption layers of the equilibrium polymers are observed from density profiles. Within this regime, the average chain length increases rapidly as the adsorption strength rising but the chain length distribution remains exponential. Compared with short chain equilibrium polymers, long chain equilibrium polymers are closer to the plates in the case of strong adsorption and are more concentrated in the middle of the gap in the case of weak adsorption. Given that the adsorption strength is weak, the forces applied to the plates are always repulsive for all separation distances. Widening the gap gives rise to a transition of the forces from repulsion to attraction if the adsorption is strong. Furthermore, the density profiles of the equilibrium polymers suggest competition among solubility, adsorption, and depletion. Higher solubility not only makes the density profiles more homogeneous but also decreases the pressures applied by the polymeric chains.

Key words: Adsorption, Equilibriumpolymer, Self-consistent field theory, Density profile, Association, Depletion effect

MSC2000: 

  • O647