Conference paper

Some Applications of a Useful Theorem in Double Layer Theory

D. G. Hall ; Unilever Research Port Sunlight Laboratory, Port Sunlight, Wirral, Merseyside, L62 4XN, England
H. M. Rendall ; Unilever Research Port Sunlight Laboratory, Port Sunlight, Wirral, Merseyside, L62 4XN, England
A. L. Smith ; Unilever Research Port Sunlight Laboratory, Port Sunlight, Wirral, Merseyside, L62 4XN, England

Abstract

The mechanisms whereby a solid-solution interface acquires
a charge are outlined and the Grahame Model of the double layer,
frequently used to interpret such phenomena is critically reviewed.
An alternative thermodynamic approach based on a recently derived
theorem is forwarded. This approach utilises the concept of an
outer Stern plane but does not require any other electrostatic concepts
inherent in the Grahame model (including the wall potential
VJ 0 ). The thermodynamic approach leads to simple tests for the
specific adsorption of non-potential determining species and provides
a general method for estimating the amounts adsorbed of
more than one species from electrokinetic data alone. It also leads
to a general method for estimating, the electro-chemical contribution
to the interaction between like or unlike plates given that
appropriate experimental data for the two isolated interfaces is
available. For surfaces fairly close to ·their isoelectric point where
amounts adsorbed are small expressions for the chemical potentials
of adsorbed species in terms of amounts adsorbed are obtained from
consideration of the expected behaviour of the surface pressure :rr:.
These expresions are very similar in form to the corresponding
expressions used with the Grahame model but are arguably more
soundly based. When used to interpret electrokinetic studies of
surfactant adsorption on solids they give excellent agreement with
experiment.
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Keywords

Hrčak ID:

194567

URI

https://hrcak.srce.hr/194567

Publication date:

5.11.1980.

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