Minnikanti Venkatachala S, Archer Lynden A
School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA.
J Chem Phys. 2005 Feb 22;122(8):84904. doi: 10.1063/1.1850452.
Variable density lattice treatment of surface enrichment of f-arm star-branched chains in star/linear polymer blends is compared with results of an analytical response theory proposed by Wu and Fredrickson [Macromolecules 29, 7919 (1996)]. We find that differences in treating the intersegmental interactions in the small interfacial region near a free surface lead to significant differences in the potentials by which polymer chain ends are attracted towards the surface. Consideration of an asymmetric relationship between segment potentials and density changes in polystyrene at 450 K and 0.1 MPa, for example, gives typically a threefold to fourfold enhancement in composition of star molecules at a vacuum interface. When contributions from gradients in density are included in the analysis even greater levels of surface enhancement (fivefold to sixfold increases) are observed. By appropriately estimating the attraction of chain ends and repulsion of branch points at a free surface, we show that concentration profiles of branched polymers predicted in the lattice model are consistent with results obtained in the analytical response theory.
将星型/线性聚合物共混物中 f 臂星型支化链表面富集的可变密度晶格处理方法与 Wu 和 Fredrickson 提出的解析响应理论结果进行了比较[《高分子》29, 7919 (1996)]。我们发现，在自由表面附近的小界面区域处理链段间相互作用的差异会导致聚合物链端被吸引到表面的势存在显著差异。例如，考虑 450 K 和 0.1 MPa 下聚苯乙烯中链段势与密度变化之间的不对称关系，在真空界面处星型分子的组成通常会提高三到四倍。当分析中包括密度梯度的贡献时，会观察到更高水平的表面富集（增加五到六倍）。通过适当估计自由表面处链端的吸引力和支化点的排斥力，我们表明晶格模型中预测的支化聚合物浓度分布与解析响应理论中获得的结果一致。
