Electrochemical characterization of the surface of a small particle and nonequilibrium electric surface phenomena

By investigating the effects that originate from nonequilibrium double layer states, it is possible to discriminate between two types of surfaces respectively corresponding and not corresponding to the standard electrokinetic model (SEM). This goal is accomplished by measuring the induced dipole moment (i.d.m.) of a particle, which enables one to determine the specific surface conductivity κ^σ, mobile charge σ_m and efficient Stern potential Ψ_ef. Porous or rough surfaces are quite abundant, but they do not correspond to SEM which implies that Ψ_ef exceeds ζ. Since ion adsorption and the stability ratio depend exponentially on Ψ_ef, substitution of the ζ potential for Ψ_ef in these exponents results in a very large error if Ψ_ef is high. The investigation of particles with a porous or a rough surface or with an anomalous conductivity confined to Stern layer ions can be quantified through integrated measurements of the nonequilibrium electric surface phenomena (NESP) used in conjunction with the extension of DLVO theory over this more complicated type of surface.NESP which are used for measurement of κ^σ are characterized and experiments are discussed which have confirmed the correctness of the theory of NESP and of the procedure for κ^σ, σ_m and Ψ_d calculation and determination of the ζ-potential under polarization conditions. A comparative evaluation of the high- and low-frequency as well as of the stationary complexes of NESP measurements is carried out, and their advantages and disadvantages are shown as they reveal themselves in electrochemical characterization. The unsuitability of the Henry-Booth equation for the interpretation of low-frequency or stationary NESP is demonstrated as well as its apparent agreement with experiment and the complete inconsistency in the case of the nonstandard model. The software, which provides a correct extraction of information about the surface of a spherical particle from data of combined electric surface investigations of real disperse systems whose particles are usually polydisperse and do not correspond to SEM, is discussed. Attention is paid to efficient methods for measuring the i.d.m. κ^σ and Ψ_ef of a nonspherical particle, based on the anisotropy of conduction and on the electro-optic phenomena.The nonlinearity of high-voltage electrophoresis caused by surface diffusion of the adsorbed ions is predicted and described. It is proposed to use this new effect for studying the dynamic Stern layer and for measuring the adsorbed ion diffusivity. Such investigations are especially important for studying the electrostatic interaction of colloid particles which has a strong effect on the kinetics of slow coagulation according to studies made by Lyklema and Dukhin. Within the framework of the Lyklema-Klein model, the effect of gel layers on the electrostatic interaction of particles is considered and on this basis the importance is shown of identification of charged gel layers and of their electrochemical characterization.