Microstructure Evolution in Polymer Latex Coatings for Whole-Cell Biocatalyst Application

The microstructure evolution of two poly(vinyl acetate-co-acrylic acid) latex coatings was elucidated by cryogenic scanning electron microscopy (cryo-SEM) and atomic force microscopy. The stages documented are particle suspension, consolidation, deformation, partial coalescence into a coherent film, and rehydration of the latter. Of particular interest is formation of a porous polymeric matrix of desired porosity and permeability of remnant interstices between deformed and partially coalesced particles; the application is to biocatalytic coatings in which viable bacteria are imprisoned in porous latex coatings. Effects of drying condition and time, rehydration behavior of latex, and the presence of glycerol on the microstructure of latex coatings were revealed by time-sectioning and cryofracture techniques of cryo-SEM. Results showed that porosity and permeability can be controlled by choice of drying and rehydration protocols. Evidence showed that glycerol retarded particle deformation, compaction, and coalescence and that substantial amounts of glycerol were expelled to the surface of the coating as drying proceeded. Implications for design of bacteria-laden and bacteria-free coating layers are discussed. Copyright 1999 Academic Press.