Abstract
A multilayer model of the
interface between a solid and a regular solution
has been developed by
treating the solution phase in the grand canonical ensemble.
The partition functions
necessary for the evaluation of the grand partition function
are obtained using either
the quasi-chemical or Bragg-Williams approximations.
The equilibrium
concentration profile normal to the interface is then found from the
maximum term in the
multiple sum for the grand partition function. The adsorption,
surface tension, and heat
of wetting for the multilayer model are derived, and
methods of obtaining the
model parameters from experimental data are suggested.
A comparison has been made
between the quasi-chemical and Bragg-TVilliams
approximations for the multilayer
model. The monolayer model is also discussed, and
compared with the
multilayer for both the solid-regular solution and the low-density
vapour-regular solution
interfaces. It is shown that the monolayer model can often be
fitted to the multilayer model
by a suitable choice of parameters. It is concluded
that in the absence of
absolute methods of obtaining the area of the solid-solution
interface, the experimental
data may not provide outright support for the multi-
layer model, but internal
inconsistencies discourage the use of the monolayer model.
There is an increasing
interest in the properties of the interface between a solid
and a non-electrolyte
solution.1 The majority of experimental studies of this type
of interface have been
restricted to the measurement of adsorption, but in some
instances the heat of
wetting as a function of bulk phase composition has also been
determined. In most cases,
the complexity of the liquid phase and the surface region
has allowed only a
qualitative interpretation of the experimental results. Neverthe-
less, there have been a few
investigations in which solutions of comparatively simple
molecules have been used
and the experimental results have been treated in a
quantitative manner.2-5
Some simple monolayer models of the solid-solution inter-
face have been proposed for
which the structure of the solid phase has been ignored,
Division of Applied
Chemistry, CSIRO Chemical Research Laboratories, Melbourne,
Vic. 3001.
Kipling, J. J.,
"Adsorption from Solutions of Non-Electrolytes." (Academic Press:
London 1965.)
Billet, D. F., Everett, D.
H., and Wright, E. H. &I., Proc. chem. Soc. 1964, 216.
3 Blackburn, A., and
Kipling, J. J., J. chem. Soc., 1954, 3819.
4 Blackburn, A., Kipling,
J. J., and Tester, D. A., J. chem. Soc. 1957, 2373.
5 Wright, E. H. &I.,
Trans. Paraday Soc., 1966, 62, 1275.
Aust. J. Chem., 1968, 21,
827-51