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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.

The influence of substrate topography and interfacial polymerization (IP) conditions were investigated during the fabrication of patterned thin-film composite (TFC) membranes. Aromatic and semi-aromatic polyamide layers were formed atop patterned ultrafiltration (UF) membrane supports by IP using different concentrations of m-phenylenediamine (MPD) or piperazine (PIP) in water of 0.01-2 % w/v with a fixed concentration of trimesoyl chloride in hexane of 0.1 % w/v. For all conditions evaluated, TFC membranes with regular surface patterns were achieved by maintaining amine soaking time and IP reaction time within 120 s. Importantly, the surface topography of the patterned TFC membranes was determined to be independent of IP reaction time. Characterization of the morphological details suggests non-conformal growth of the barrier layer on the patterned UF substrates. Results indicate that the extent of such non-conformal growth can be reduced by decreasing the amine concentration as well as by choosing an amine monomer such as PIP that produces a thinner semi-aromatic barrier layer. The overall findings of this study provide a means for achieving desired surface features for specific membrane applications.

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Surface roughness of membranes is often perceived by many as a factor that promotes fouling during filtration, and thus is undesirable. Almost all liquid-based separation membranes display flat surfaces with intrinsic surface roughness that is associated with the membrane manufacturing process. Recently, polymer ultrafiltration (UF) and thin film composite (TFC) membranes containing regular, periodic surface patterns were fabricated using cost-effective lithographic methods. Here, we review the work to-date on the fabrication and characterization of these patterned membranes with a focus on processing-structure-performance relationships.In addition, the antifouling performance of these membranes against model foulants including colloidal suspensions and protein solutions are also highlighted.