Shrinkage effects during polymer phase separation on microfabricated molds

Phase separation microfabrication (PSμF) is a fabrication method that allows the preparation of membranes having micropattern surface topologies. PSμF entails the phase separation of a polymer solution cast onto structured supports. The polymer solution wets the features and upon phase separation and solidification the polymer replicates the underlying microstructure. Shrinkage of the solidifying polymer solution influences the replication precision. Through the systematic study of a PES/PVP/NMP/water system, the relation between polymer concentration and replication performance was assessed. Normal shrinkage (thickness) is found to be dependent on polymer concentration, with pore sizes varying between two limits. Outside these limits, the pore size does not vary with polymer concentration and shrinkage scales inversely with it. Lateral shrinkage proceeds according to the same mechanism. Yet, its extent is lower. Influence of the mold features on the shrinkage of the replicas and the deformation of the overlying film is explained in terms of feature size and distribution, along with the porosity of the film.