CHARACTERIZATION OF PSS PDADMAC-CO-AA POLYELECTROLYTE COMPLEXES AND THEIR STOICHIOMETRY USING ANALYTICAL ULTRACENTRIFUGATION/

Analytical ultracentrifugation was successfully applied to the determi nation of the complex composition and characterization of the particle s of water insoluble polyelectrolyte complexes between sodium poly(sty renesulfonate) (PSS) and copolymers of various ratios of diallyldimety lammonium chloride (DADMAC) and acrylamide (AA). Sedimentation velocit y experiments in an analytical ultracentrifuge with absorption optics allow the observation of individual species in a system of strongly po lydisperse, aggregated particles of colloidal level in the presence of free polymer. It was found that the complexes are remarkably polydisp erse and form nonstoichiometric particles including the major componen t in considerable excess. The stoichiometry factor depends strongly on the ionic strength of the solution and the concentration of the compo nents. At low initial mixing ratios and ionic strengths of about 10(-2 )-10(-3) N, sedimentation equilibrium experiments can be performed. Th e results of the evaluation of free PSS and complex concentration grad ients using the Omega-function are similar to the findings obtained wi th sedimentation velocity experiments. A model where secondary aggrega tes are surrounded by free polymers is discussed for the sedimentation of these particles. It is demonstrated that polyelectrolyte complexes with the copolymer containing 50% DADMAC and AA form comparatively mo nodisperse species in aqueous salt solution having sedimentation coeff icients between 4 and 40 Sv.