Nonlinear hairy layer theory of electrophoretic fingerprinting applied to consecutive layer by layer polyelectrolyte adsorption onto charged polystyrene latex particles

The consecutive layer-by-layer adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrene-sulfonate) (PSS) on colloidal charged latex particles is investigated by measuring the electrophoretic mobility as a function of pH and ionic strength over a broad range (electrophoretic fingerprinting). Meaningful interpretation of the data required the development of a nonlinear approach to hairy particle electrophoresis including dissociation, adsorption, and association. Steric and electrostatic exclusion of mobile ions from the hairy layer has been considered. Also, the surface conductivity correction is extended to the case of charged hairy layer particles. We deposited up to three polyelectrolyte layers. The following were found: (i) Each layer deposition is accompanied by charge overcompensation and (ii) Not only the top layer but also the underneath layers and the naked latex particle surface contribute to the particle mobility. This can be interpreted as an incomplete coverage or a polyelectrolyte interpenetration. (iii) The thickness of the top adsorbed hairy layer is of the order of 1 nm. (iv) About one-third of the charged groups of the top layer form ion pairs with the underneath charges. (v) Counterion adsorption to the charged groups of the top layer can be observed.