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 sur faces respectively corresponding and not corresponding to the standard electrokinetic model (SEM). This goal is accomplished by measuring th e induced dipole moment (i.d.m.) of a particle, which enables one to d etermine the specific surface conductivity kappa(sigma), mobile charge sigma(m) and efficient Stern potential Psi(ef). Porous or rough surfa ces are quite abundant, but they do not correspond to SEM which implie s that Psi(ef) exceeds zeta. Since ion adsorption and the stability ra tio depend exponentially on Psi(ef), substitution of the zeta potentia l for Psi(ef) in these exponents results in a very large error if Psi( ef) is high. Tile 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 nonequilibri um electric surface phenomena (NESP) used in conjunction with the exte nsion of DLVO theory over this more complicated type of surface. NESP which are used for measurement of kappa(sigma) are characterized and e xperiments are discussed which have confirmed the correctness of the t heory of NESP and of the procedure for kappa(sigma), sigma(m) and Psi( d) calculation and determination of the zeta-potential under polarizat ion conditions. A comparative evaluation of the high- and low-frequenc y as well as of the stationary complexes of NESP measurements is carri ed out, and their advantages and disadvantages are shown as they revea l themselves in electrochemical characterization. The unsuitability of the Henry-Booth equation for the interpretation of low-frequency or s tationary NESP is demonstrated as well as its apparent agreement with experiment and the complete inconsistency in the case of the nonstanda rd model. The software, which provides a correct extraction of informa tion about the surface of a spherical particle from data of combined e lectric surface investigations of real disperse systems whose particle s are usually polydisperse and do not correspond to SEM, is discussed. Attention is paid to efficient methods for measuring the i.d.m. kappa (sigma) and Psi(ef) of a nonspherical particle, based on the anisotrop y of conduction and on the electro-optic phenomena. The nonlinearity o f high-voltage electrophoresis caused by surface diffusion of the adso rbed ions is predicted and described. It is proposed to use this new e ffect for studying the dynamic Stern layer and for measuring the adsor bed 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 studi es made by Lyklema and Dukhin. Within the framework of the Lyklema-Kle in 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 char acterization.