a b s t r a c tImparting sub-micron periodic patterns on the surface of ultrafiltration (UF) membranes has been shown to improve their antifouling characteristics. However, the deformation mechanism underlying membrane surface-patterning with nanoimprint lithography (NIL) is currently unclear. In response to this need, this study addresses the influence of nanoimprinting on the structural and performance characteristics of a commercial polyethersulfone (PES) UF membrane. The work utilized a flat (no pattern) as well as a pattern-containing mold such that local surface deformation associated with pattern formation could be isolated from the overall mechanical deformation in compression. The mechanical properties of the UF membrane as a function of temperature and deformation rate were characterized, and the overall thickness, molecular weight cutoff, and DI water permeance were measured for membranes imprinted using the flat mold. The data show that the influence of the NIL process on the membrane structure is length-scale dependent. Furthermore, imprinting of the UF membrane with the pattern-containing mold was examined experimentally as well as with finite element simulation. Results indicate that the nonuniform contact deformation at the membraneemold interface provides the potential to optimize the NIL conditions for achieving desired pattern geometries without significantly increasing the membrane resistance.

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.