Investigation of Dynamic Stern Layer of Liposomes by Measurements of Conductivity and Electrophoresis

Abstract

Ionic surface diffusitivity is important parameter for the electrostatic interaction between colloid particles and hence its measurement is a new important factor for the surface characterization of colloid particles. If the adsorbed ion mobility is small the approximation of the interaction at constant charge can be valid,but in opposite case the charge regulation occurs during their interaction. The large surface diffusitivities of polyvalent ions adsorbed on negatively charged liposomes are found combining measurements of conductivity and electrophoresis. At a rather low surface charge and high adsorbability of polyvalent cations, the diffuse-layer charge can be very small in comparison with the Stern-layer charge, which can predominate in surface conductivity and provide information about the diffusitivity of adsorbed ions if it is not small. An efficient and simple method for the discrimination between small and large surface diffusitivities of adsorbed ions based on the determination of both iso-electric point and iso-conducting point is proposed and experimentally proved.