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The Sol Concentration Effect in n-Butylammonium Vermiculite Swelling

Published online by Cambridge University Press:  28 February 2024

G. D. Williams ,
K. R. Moody ,
M. V. Smalley  and
S. M. King
G. D. Williams
Affiliation:
Physical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ, United Kingdom
K. R. Moody
Affiliation:
Physical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ, United Kingdom
M. V. Smalley*
Affiliation:
Polymer Phasing Project, ERATO, JRDC, Keihanna Plaza 1–7 Hikari-dai, Seika-cho, Kyoto 619-02, Japan
S. M. King
Affiliation:
ISIS Science Division, Rutherford Appleton Laboratory Chilton, Didcot, Oxon, OX11 OQX, United Kingdom
*
1To whom correspondence should be addressed.
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Abstract

The swelling of n-butylammonium vermiculite in water was investigated as a function of the sol concentration (r), the salt concentration (c) and the temperature (T).

The interlayer spacing in the gel phase was investigated as a function of r and c by neutron diffraction and by laboratory experiments which measured how many times its own volume a crystal would absorb. The salt concentration was found to be the stronger variable with the interlayer spacing decreasing proportional to c0.5, which is consistent with previous results and with the Coulombic attraction theory. The sol concentration was found to affect the swelling for two reasons, the salt fractionation effect and the trapped salt effect. Both of these cause the salt concentration in the supernatant fluid to be greater than that originally added to the crystals and so reduce the swelling.

A new method was used for extracting the solution from inside the gels by collapsing the gels by the addition of potassium hydrogen carbonate. The Volhardt titration was carried out on the extracted and supernatant solutions from about 250 gels. The ratio of the external to the internal chloride concentration was found to be approximately constant across the range of salt concentrations. Its average value was equal to 2.6, again in agreement with Coulombic attraction theory and showing the surface potential to be constant at about 70 mV.

The (r, c, T) boundary of the two phase colloid region was investigated by three methods. A plot of log c against Tc was linear within experimental accuracy, with a gradient of 0.077 K−1 or 13 K per log unit. This shows that the surface potential varies by only 1 mV per decade in the salt concentration. The system is therefore governed by the Dirichlet boundary condition and not by the Nernst equation.

Keywords

CATDLVO theoryNeutron diffractionOsmotic swellingPhase transitionsSalt fractionationTrapped saltVermiculite gels
Type
Research Article
Information
Clays and Clay Minerals , Volume 42 , Issue 5 , October 1994 , pp. 614 - 627
Copyright
Copyright © 1994, Clay Minerals Society

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