In the absence of electric fields or hydrostatic pressure, mass transport through various forms of polyelectrolyte complex, including multilayers, occurs via diffusion. The rate of transport depends strongly on the moving species. Transport of small molecules and ions is the fastest and occurs at similar rates as through dense hydrogels. The diffusion of polymer molecules is many orders of magnitude slower. In between these two extremes is the diffusion of defects or extrinsic sites, which are polyelectrolyte repeat units compensated by a counterion. Using values of diffusion coefficients obtained from experiments on polyelectrolyte complexes and multilayers made from poly(styrene sulfonate), PSS, and poly(diallyldimethylammonium), PDADMA, this talk will show how defect diffusion is responsible for the regular layer-by-layer accumulation of polymer during multilayer buildup. Included will be an explanation of how higher-mobility polyelectrolytes (PDADMA, in this case) appear to travel “through” strata of lower-mobility polyelectrolytes (here, PSS).

Three types of diffusion in polyelectrolyte complexes and multilayers

254th National Meeting (2017)

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