The presence of inhomogeneities or feature’s gradients along polymer foams is usually an undesired defect inherent to their fabrication routes. On the contrary, accurate control of the heterogeneity of the polymer foam’s features, such as the pore size, could allow mimicking some high-performance natural materials and enhancing the performance of these polymer foams in different applications. However, up to now the controlled fabrication of foams with a well-controlled heterogeneity has not been successfully achieved.
With this aim, it was developed an approach to locally control, for the first time, the cell nucleation density of different regions of a polymer foam. A thermally induced in situ synthesis of nanoparticles were employed to create regions filled with ZnO nanoparticles on poly(methyl methacrylate) (PMMA)/Zn(OAc)2 films. In this way, templated solid PMMA samples with well-differentiated regions, presenting or not ZnO nanoparticles, were obtained. Finally, from this templated solid samples it was possible to obtain, by gas dissolution foaming and taking advantage of the heterogeneous nucleation induced by the ZnO nanoparticles, PMMA-based templated foams with well-defined areas of different cell sizes, reaching cell sizes about 500 nm in the areas filled with ZnO nanoparticles.