USE OF NEUTRON REFLECTION AND SPECTROSCOPIC ELLIPSOMETRY FOR THE STUDY OF THE INTERFACE BETWEEN MISCIBLE POLYMER-FILMS

Specular neutron reflection (NR) and spectroscopic ellipsometry (SE) were used to investigate the interface between thin films of the miscible pair poly(vinyl methyl ether) (PVME) and polystyrene (PS). Interdiffusion of PVME (T(g) = -31-degrees-C) into PS (T(g) = 104-degrees-C) was quite rapid at temperatures more than 25-degrees-C below the glass transition of polystyrene. The rate of change of the interface penetration depth into PS at 76-degrees-C was markedly non-Fickian with an observed linear dependence with time. Interface profiles and interface dimensions were determined before and after annealing by the two techniques. Before annealing the interfacial thickness varied between 5 and 22 nm depending on original film thicknesses, and after annealing at 76-degrees-C the interface broadened to approximately 55 nm. The factors controlling the broadening of the interfaces are discussed. Some evidence of asymmetric interfacial profiles with a low volume fraction of the more mobile PVME penetrating into the PS phase was also obtained with both techniques. The linear dependence with time and interface profile could be interpreted in terms of a case II diffusion process, which is typically seen for solvent penetration into glassy polymers.