Influence of nanoimprint lithography on membrane structure and performance

Imparting 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 non-uniform contact deformation at the membrane–mold interface provides the potential to optimize the NIL conditions for achieving desired pattern geometries without significantly increasing the membrane resistance. a) Schematic illustration of surface patterning a commercial ultrafiltration membrane with NIL. b) Typical stress–strain curves of the PES membrane during tensile tests at different temperatures at a strain rate of 0.01s−1; c) The contours of normal stress in the vertical direction of a deformed porous membrane under applied pressure of 4 MPa. [Display omitted] •Mechanical properties of porous membranes are characterized.•The deformation of the membranes are length-scale dependent.•Mechanical deformation and performance of the membranes are compared.