Relaxation of Thin Films of Polystyrene Floating on Ionic Liquid Surface

We have investigated the dynamics of polymer films, free of physical constraints, floating on the surface of an ionic liquid (IL) to minimize substrate−polymer interactions and constraints arising from the adhesion of the polymer to the substrate. ILs, which have a negligible vapor pressure, were used to support polystyrene (PS) thin films to investigate the relaxation behavior and glass transition temperature ( T g ) of thin polymer films. Freely floating films relaxed when heated to the temperatures above the bulk T g, resulting in a thickening of the film and a concomitant shrinkage in the lateral dimensions of the film. The relaxation behavior depended on the temperature, film thickness, and molecular weight of the polymer. Completely relaxed films showed T g values similar to that in the bulk, independent of the initial thicknesses, molecular weight, and cooling rate.