Effect of solvent evaporation rate on thermally stimulated current spectra of solution-cast PMMA films

Thermally stimulated current (TSC) spectra, isothermal surface potential decay (ITSPD) and morphology were examined for polymethylmethacrylate (PMMA) films cast from an acetonic PMMA solution at variously controlled evaporation rates of the solvent. Observed TSC spectra, ITSPD and morphology for these films remarkably depended on the solvent evaporation rate. At high evaporation rates, charge retention power of these films was large and their appearance became white and cloudy. Fine cellular structure of about 300 μm formed by Benard convection was also found in the films cast at high evaporation rates. Deep charge traps were found in the central parts of the Benard convection cells by a charge-visualization technique with fine dye particles. While, at low evaporation rates, charge decay in the PMMA cast films was fast and the films were transparent in their appearance. Annealing the cloudy PMMA films at 130°C for 1 hour destructed their cellular structure and made them transparent.