Relationship between permeation and deformation for porous membranes

Most polymeric membranes are engineered to have high porosity in order to reduce transport resistance of the permeate(s). However, since most polymers are relatively compliant and exhibit time-dependent behavior, such membranes are prone to deformation under mechanical loading that can occur during different stages of manufacturing as well as during separation. Therefore, it is of critical importance to understand the influence of mechanical deformation on the permeability of the membranes. However, an appropriate relationship has not been established due to the lack of methods that can precisely control membrane deformation and the significant variability of membrane properties. Here, we report the systematic and quantitative examination of the permeability-deformation relationship for microfiltration (MF) and ultrafiltration (UF) membranes with different pore structure and chemistry. Polymer membranes were deformed to different levels of compressive strain using nanoimprint lithography with systematically different processing conditions. Furthermore, permeation measurements were carried out on each membrane sample before and after the compressive deformation to minimize membrane variability concerns. The experimental results reveal that the permeability of the MF and UF membranes decreases with the increase of compressive strain such that the dependency approaches the behavior of an open-cell foam. The derived relationship is simple but useful despite key differences between open-cell foams and porous membranes including pore structure asymmetry and the much smaller pore size of the latter.