@article{siripurapu_coughlan_spontak_khan_2004, title={Surface-constrained foaming of polymer thin films with supercritical carbon dioxide}, volume={37}, ISSN={["1520-5835"]}, DOI={10.1021/ma0484983}, abstractNote={Microcellular polymer foams afford a wide variety of attributes relative to their dense analogues, and efforts remain underway to establish viable routes to generate foams with substantially reduced pore cell size and increased pore cell density. Barrier constraints are applied in the present work to achieve diffusion-controlled isothermal foaming of thin polymer films in the presence of supercritical carbon dioxide (scCO2). Poly(methyl methacrylate) (PMMA) films measuring ca. 95−100 μm in thickness are physically constrained between two impenetrable plates so that scCO2 exit diffusion is restricted to the film edges. Results obtained here demonstrate that the pore size can be systematically reduced to less than 100 nm in such systems by applying high saturation scCO2 pressures, relatively low foaming temperatures (near the glass transition temperature of the scCO2-plasticized polymer), and a rapid pressure quench. Classical nucleation theory (CNT) modified to account for the compressible nature of scCO2 ...}, number={26}, journal={MACROMOLECULES}, author={Siripurapu, S and Coughlan, JA and Spontak, RJ and Khan, SA}, year={2004}, month={Dec}, pages={9872–9879} }