Deposition of composite coatings from particle-particle and particle-yeast blends by convective-sedimentation assembly

The structures resulting from convective-sedimentation assembly (CSA) of bimodal suspensions (4.1-10% solids) of strongly charged sulfate latex microspheres (zeta potential -55.9 +/- 1.8 mV at pH 8.0) and weakly charged Saccharomyces cerevisiae (zeta potential -18.7 +/- 0.71 mV at pH 8.0) on glass, polyester, polypropylene, and aluminum foil substrates was evaluated. This study shows how substrate wettability, suspension composition, particle size ratio and surface charge affect the deposition process and resulting coating microstructure (particle ordering and void space). Size ratio and charge influence deposition, convective mixing or demixing and relative particle locations. Substrate wettability and suspension composition influence coating microstructure by controlling suspension delivery and spreading across the substrate. S. cerevisiae behave like negatively-charged colloidal particles during CSA. CSA of particle-yeast blends result in open-packed structures (15-45% mean void space), instead of tightly packed coatings attainable with single component systems, confirming the existence of significant polymer particle-yeast interactions and formation of particle aggregates that disrupt coating microstructure during deposition. Further optimization of the process should allow void space reduction and deposition of cells plus adhesive polymer particles into tightly packed adhesive monolayer coatings for biosensors, biophotoabsorbers, energy applications, and highly reactive microbial absorbers. (C) 2012 Elsevier Inc. All rights reserved.