Dispersion phenomena and the glass transition in thin polymer films
We have studied morphologies forming in films of polyisoprene capped on both sides by polystyrene layers. As the films are heated from room temperature, a periodic, lateral morphology develops which disappears near the bulk glass transition temperature 'Tg' of polystyrene for large heating rates. At 110°C, holes form and grow within the polyisoprene layer of the trilayer films and we have characterized their growth as a function of polystyrene and polyisoprene thicknesses. We compare the results with those obtained previously for freely-standing polystyrene films. We have studied freely-standing films of cyclic polystrene and films of linear polystyrene of similar molecular weight. We have measured the temperature dependence of the thickness and the index of refraction of the films and relate these measurements to 'Tg', chain diffusion and anisotropy. Chain diffusion was further studied by measuring the growth of holes in the films as a function of film thickness and temperature.