Free surfaces of polymer blends. II. Effects of molecular weight and applications to asymmetric polymer blends

Abstract

The composition of the free surface of a binary polymer blend has been investigated in this work as a function of molecular weights, energetic parameters, and composition. The approach involved the use of a compressible mean-field lattice model that was developed in the spirit of the Scheutjens and Fleer theory of polymer solutions [J. Chem. Phys. 98, 6516 (1993)]. For symmetric polymer blends it was found that the surface segregation was driven by the degree of incompatibility of the blend, with the segregation increasing monotonically with the quantity χ1,2 r. These results are in qualitative agreement with conclusions obtained from an incompressible model for polymer blends near a surface, and suggests that the inclusion of compressibility effects do not change the predicted surface segregation significantly in these cases. In contrast, the behavior of isotopic polymer blends of disparate molecular weights, which could not be reproduced in the case of incompressible models, can be captured by the compressible model [J. Chem. Phys. 98, 4163 (1993)]. This fact therefore stresses the importance of compressibility effects in the context of segregation to free surfaces, especially for blends of disparate molecular weight polymers, and suggests that such models have to be utilized to incorporate all of the physics in these situations.

Influence of Osmotic Pressure on Nanostructures in Thin Films of a Weakly-Segregated Block Copolymer and Its Blends with a Homopolymer

“…Thus, the patchy PS overlayer may be due to partial surface aggregation from short PS 6 chains. Such surface aggregation of short chains in our system is similar to the segregation behavior of short chains in a binary mixture of two homopolymers with different molecular weights [ 56 , 57 ].…”

Anomalous Dynamics of Polymer Films

“…ratio). 24 For a binary blend of polymers with disparate molecular weights, Hariharan et al 61 showed that entropic effect would drive the low-M w component to the film surface, producing a local enrichment of the low-M w component. Thus, one expects the 13.7 K constituent in the blend films to segregate to the surface.…”

The Role of Intefacial Diffuseness on Surface Segregation From Polymer Blends

“…Hariharan et al (16,19,23,24) conducted mean-field Scheutjens-Fleer calculations for the surface segregation from miscible polymer mixtures. They considered the segregation to both neutral hard surfaces, and to the free air surface.…”