Surface segregation in polymer blends due to stiffness disparity

Abstract

The entropy-driven surface segregation of polymer blends is investigated via computer simulations and integral equation theory. The model system is composed of a binary blend at a hard wall where one of the components of the blend is stiffer than the other. It is found that, at meltlike densities relevant to experiments, both simulations and microscopic theory predict the segments of the stiffer chains segregate to the surface.

Inversion Symmetry, Architecture and Dispersity, and Their Effects on Thermodynamics in Bulk and Confined Regions: From Randomly Branched Polymers to Linear Chains, Stars and Dendrimers

“…In particular, we find that smaller species segregate to the neutral surface, as expected. In the blend, we find the enrichment of the neutral surface by chains, which has been suggested earlier for small structural differences [30,31,36]. However, our results are inconsistent with the known results [31b,36] on the behaviour of endgroups and surface enrichment in the above blend.…”

“…Hence, such a theory allows us to predict many of these microscopic parameters like the chi parameter from experimental measurements, provided the theory is based on a realistic model of the system. Current interest has been to understand whether architecture plays an important role in determining nonuniversal properties like the effective chi parameter and behaviour near surfaces, or universal properties like the exponents [17,20,22,23,26,[28][29][30][31][32][33][34][35][36][37][38]42,43]. Statistical mechanics also enables us to separate out the entropic contribution from the energetic contribution to understand the effect of architectural differences.…”

Surface segregation of conformationally asymmetric polymer blends

“…It was found that for polymer blends composed of polymers with different degree of polymerization but of chemically identical monomers, shorter polymers are in excess at the wall. It was also demonstrated in simulations [4,11] and supported by calculations using the integral equation theory [18] that stiffer polymers are present in excess in the vicinity of the wall. However the self-consistent field theory developed in Ref.…”

“…Recently there has been a big deal of attention on the surface segregation due to conformational asymmetry of the molecules of the polymer blend and due to differences in topology [4,8,9,10,11,12,13,14,15,16,17]. It was established that the composition of polymer blends in the vicinity of surfaces can be different from the bulk composition even for neutral surfaces.…”

“…There exist more rigorous approaches, which allow one to derive the concentration profiles starting from the microscopic polymer statistics in the presence of a surface. One of such microscopic approaches is the integral equations method which can be applied to various sitesite or hard-particle models of a dense polymeric system [4]. This method having many advantages such as ability to predict microscopic correlations between different types of monomers and between monomers and surfaces requires a considerable amount of numerical computations.…”