Engineering the Microstructure and Permeability of Thin Multilayer Latex Biocatalytic Coatings Containing E. coli

The microstructure and permeability of rehydrated 20—100 m thick partially coalesced vinyl-actetate acrylic copolymer) SF091 latex coatings and a 118 /m thick model trilayer biocatalytic coating consisting of two sealant SF091 layers containing a middle layer of viable E. coli HBIOI + latex were studied as delaminated films in a diffusion apparatus with KNOs as the diffussant. The permeability of the hydrated coatings is due to diffusive transport through the pore space between the partially coalesced SF091 latex particles. Coating microstructure was visualized by fast freeze cryogenic scanning electron microscopy (cryo-SEM). The effective diffusion coefficient of SF091 latex coatings (diffusive permeability/film thickness) was determined as the ratio of the effective diffusivity of KNOs to its diffusivity in water (Peff/D). Polymer particle coalescence was arrested by two methods to increase coating permeability. The first used glycerol with coating drying at 4 °C, near the glass transition temperature (Tg). The second method used sucrose or trehalose as a filler to arrest coalescence; the filler was then dissolved away. DD was measured as a function of film thickness; content of glycerol, sucrose, and trehalose; drying time; and rehydration time. D^D varied from 3 x 10 for unmodified SF091 coatings to 6.8 x 10 for coatings containing sucrose. D D was reduced by the flattening of latex particles against the surface of the solid substrate, as well as by the presence of the colloid stabilizer hydroxyethyl-