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 hydrochlo ride) (PAH) and poly(styrene-sulfonate) (PSS) on colloidal charged lat ex particles is investigated by measuring the electrophoretic mobility as a function of pH and ionic strength over a broad range (electropho retic fingerprinting). Meaningful interpretation of the data required the development of a nonlinear approach to hairy particle electrophore sis including dissociation, adsorption, and association. Steric and el ectrostatic exclusion of mobile ions from the hairy layer has been con sidered. Also, the surface conductivity correction is extended to the case of charged hairy layer particles. We deposited up to three polyel ectrolyte layers. The following were found: (i) Each layer deposition is accompanied by charge overcompensation and (ii) Not only the top la yer but also the underneath layers and the naked latex particle surfac e contribute to the particle mobility. This can be interpreted as an i ncomplete coverage or a polyelectrolyte interpenetration. (iii) The th ickness 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.