Surface segregation in athermal polymer blends due to conformational asymmetry

Abstract

Monte Carlo simulations are used to investigate the surfaces of athermal blends of stiff and flexible polymers as the bending modulus of the stiff polymers, kappa, is increased from zero to the point where the bulk undergoes an isotropic-nematic transition. For hard walls characteristic of polymer/solid surfaces, the flexible polymers generally segregate to the surface. However, just prior to the bulk transition, a surface transition occurs where a thin nematic layer rich in stiff polymers forms next to the wall. This appears to be followed by a second surface transition where the degree of order abruptly increases, which in turn causes a rapid thickening of the nematic layer that nucleates the bulk nematic phase. For soft boundaries representative of polymer/air surfaces, a thin layer rich in stiff polymers but without nematic order forms on the outer edge of the surface with a more significant layer rich in flexible polymers beneath. In this case, the surface transitions are lost and the qualitative behavior remains unchanged as kappa increases.