Solid‐state microcellular and nanocellular polysulfone foams

In this article, we report on the process for creating microcellular and nanocellular polysulfone (PSU) foams. Microcellular foams with cell size up to 8 µm and nanocellular foams with cell size in the range of 20–30 nm were created. A range of CO2 concentration was achieved by varying saturation temperature, from 5% at 60 °C to 14.7% at −10 °C. The CO2 concentration has a strong influence on the cellular structure. There exists a critical concentration window, between 10.7% and 12.3%, within which cell nucleation densities increase rapidly and cell sizes drop from micrometer range to below 1 µm into the nanometer range. Nanofoams with cell nucleation densities exceeding 1015 cells/cm3 and void fraction of up to 48% are achieved. At the high CO2 concentration region, the change from closed nanocellular structure to bicontinuous nanoporous structure is observed. Also, nanostructures on the cell wall of microcells are observed and believed to be formed via stress-induced nucleation/spinodal decomposition. The PSU nanofoams produced in this study present an opportunity to produce polymer nanofoams with a relatively high service temperature. The ability to create cells of different length scales provides an opportunity to study the effect of cell size on the foams properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 975–985