Antimicrobial Janus Filters that Break Oil-in-Water Emulsions and Separate Oil

Separation of oil from emulsions is industrially important. Existing Janus filters that bear a de-emulsifier on one surface and a hydrophobic polymer on the opposite side can break oil-in-water emulsions and selectively separate the coalesced oil. This paper reports a Janus filter that possesses the additional function of being antimicrobial. This filter is prepared by aero-spraying one side of a cotton fabric with a solution of a copolymer containing the hydrophobic poly(dimethylsiloxane) (PDMS) and soaking the other side in a solution containing a copolymer of dimethylaminoethyl methacrylate (DMAEMA). The fabric is then baked in an oven to cross-link the polymers around the cotton fibers. The DMAEMA-bearing side is further reacted with benzyl bromide to produce quaternized DMAEMA. The latter coalesces oil droplets stabilized by an ionic surfactant most likely via two mechanisms: fusion of different oil droplets around the charged fibers and fusion of overlapping oil droplets adsorbed on the fibers. The adsorption occurs probably due to the displacing of the surfactant molecules on the droplet surfaces by the surfactant-like quaternized DMAEMA units. The coalesced oil is then drawn to the hydrophobic PDMS side that repels water and gets separated from the emulsion. Moreover, the quaternary amine is antimicrobial, killing the model bacterium E. coli under various conditions, and impedes filter contamination by microorganisms. These trifunctional filters with further performance improvement may find practical applications.