Macroion adsorption− electrokinetic and optical methods

Michna, Aneta

Macroion adsorption− electrokinetic and optical methods

Abstract

Recent studies on macroion adsorption at solid/ liquid interfaces evaluated by electrokinetic and optical methods are reviewed. In the first section the description of the electrokinetic phenomena at solid surface is briefly outlined. Various methods for determining both the static and the dynamic properties of electrical double layer, such as: the appropriate location of the slip plane, were presented. The theoretical approaches are discussed concerning quantitative interpretation of the streaming potential/ current measurements of homogeneous macroscopic interfaces, both bare and formed by microsphere adsorption. Experimental results are presented, involving the electrokinetic characteristics of bare surfaces, such as mica, silicon, glass etc. obtained from various types of electrokinetic cells. The effect of surface conductivity on the zeta potential was underlined. In the next section, various theoretical approaches, proposed to determine the distribution of electrostatic potential and flow distribution within macroion layers, were disscused. Accordingly, the influence of the uniform as well as non−uniform distribution of charges within macroion layer, the dissociation degree, and the surface conductance on electrokinetic parameters were discussed. The last section was devoted to the discussion of experimental data obtained by the streaming potential/ current measurements and optical methods, such as reflectometry, ellipsometry, surface plasmon resonance (SPR), colloid enhancement, and fluorescence technique, for mono− and multilayers of macroions. Results of polcations (PEI, PAMAM dendrimers, PAH, PDADMAC) and polyanions (PAA, PSS) adsorption on mica, silicon, gold, and PTFE are quantitatively interpreted in terms of theoretical approaches postulating the three dimensional charge distribution or random sequential adsorption model (RSA). Macroion bilayer formation, experimentally examined by streaming current measurements, and theoretically interpreted in terms of the comprehensive formalism was also reviewed. The utility of the electrokinetic measurements, combined with optical methods, for a precise, in situ characteristics of macroion mono− and multilayer formation at soid/ liquid interfaces is pointed out.