A Lattice Model for the Surface Segregation of Polymer Chains Due to Molecular Weight Effects

Abstract

The effects of polydispersity on the behavior of a polymer melt near a surface are considered in this work. To study these effects we have modeled an athermal polymer melt with a bimodal molecular weight distribution in the vicinity of a neutral surface in the spirit of the mean-field lattice treatments of Sheutjens and Fleer20 and Theodorou.23 The results of the calculations show that purely entropic effects cause the shorter chains in the system to partition preferentially to the surface. This partitioning becomes more pronounced with increases in the difference between the molecular weights of the chains. The concentration profile of the segments of any one species in the vicinity of the wall can be described by a hyperbolic tangent function with a single correlation length that is a simple function of the mixture composition and the radii of gyration of the two chains. Implications of these results on the surface tension and orientation of chain segments in the interface of a bimodal polymer melt are also examined. © 1990, American Chemical Society. All rights reserved.