Versatile surface micropatterning and functionalization enabled by microcontact printing of poly(4-aminostyrene).

Microcontact printing (µCP) of polyelectrolytes is a facile and powerful method for surface micro/nanopatterning and functionalization. Poly(4-aminostyrene) (PAS) is a polyelectrolyte that can be converted to aryldiazonium salt and exhibits pH-dependent hydrophobicity. Here we demonstrate µCP of PAS and the expansion of this technique in various directions. First, the microcontact-printed PAS can be diazotized to micropattern biomolecules including DNA and protein and nanomaterials including single-walled carbon nanotubes and gold nanoparticles. Second, the diazotized PAS enables µCP of a metallic structure on a carbon surface. Third, the hydrophobic nature of PAS at the neutral pH allows the microcontact-printed PAS-based polyelectrolyte multilayer to be used as masks for wet etching. Lastly, this technique allows facile fabrication of highly engineered microparticles with a unique structure. Overall, this work has established a novel µCP platform with various potential applications.

Development of anti-biofouling feed spacers to improve performance of reverse osmosis modules.

This study investigates the biofouling resistance of modified reverse osmosis (RO) feed spacers. Control spacers (made of polypropylene) were functionalized with a biocidal coating (silver), hydrophilic (SiO2 nanoparticles) or superhydrophobic (TMPSi-TiO2 nanoparticles) anti-adhesive coatings, or a hybrid hydrophilic-biocidal coating (graphene oxide). Performance was measured by adhesion assays, viability tests, and permeate flow decline in a bench scale RO system. The control spacers proved to be one of the better performing materials based on bacterial deposition and dynamic RO fouling experiments. The good anti-adhesive properties of the control can be explained by its near ideal surface free energy (SFE). The only surface modification that significantly reduced biofouling compared to the control was the biocidal silver coating, which outperformed the other spacers by all measured indicators. Therefore, future efforts to improve spacer materials for biofouling control should focus on engineering biocidal coatings, rather than anti-adhesive ones.