Finite-size effects on surface segregation in polymer blend films above and below the critical point of phase separation

We investigate the influence of temperature and confinement, on surface segregation in thin films of deuterated polybutadiene and polyisoprene near the critical point for phase separation. Neutron reflectivity measurements show that, polyisoprene enriches at the air and silicon interfaces in both the 1- and 2-phase region. A transition between in-plane and surface-directed (layered) phase separation is observed with increasing film thickness. Weak critical adsorption effects cause the blend composition profile to be rounded in comparison with profiles normally measured in small liquid mixtures.