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The surface energies of cation substituted Laponite

Published online by Cambridge University Press:  09 July 2018

J. Norris
Affiliation:
Department of Geology, State University of New York, 4240 Ridge Lea, Amherst NY 14226
R. F. Giese
Affiliation:
Department of Geology, State University of New York, 4240 Ridge Lea, Amherst NY 14226
P. M. Costanzo
Affiliation:
Unilever Research, US, Inc., 45 River Road, Edgewater NJ 07020
C. J. van Oss
Affiliation:
Departments of Microbiology and Chemical Engineering, State University of New York, 3435 Main Street, Buffalo NY 14214, USA

Abstract

Laponite RD forms stable, coherent films which adhere strongly to glass slides. Such films are capable of supporting liquid drops allowing the direct measurement of contact angles for five liquids of which, two were apolar (0:-bromonaphthalene and diiodomethane) and three were polar (water, formamide, glycerol); surface tension components and parameters (γLw, γ and γ) were determined by solving the Young equation. These determinations were made for homoionic samples saturated with Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba and NH4 as well as the natural material. Whereas the values of γLw (the apolar Lifshitz-van der Waals component) varied only within narrow limits (41-44 mJ/m2), the Lewis base parameter varied comparatively widely (24-41 mJ/m2). The Lewis acid parameter was small and relatively constant (1·3-3·0 mJ/m2). The variation of γ as a function of the exchangeable cation suggests that the divalent cations are shielded from the silicate surface by the water molecules of their sphere of hydration, whereas the monovalent cations are in direct contact with the oxygen atoms of the silicate surface. Furthermore, the divalent cations may screen the Lewis base sites to a greater degree than do the monovalent cations. Lithium behaves anomalously and this may indicate that it physically enters into the ditrigonal hole in the silicate layer.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

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