The intercalation of a vermiculite by cationic surfactants and its subsequent swelling with organic solvents.
We have measured the dimensions of the interlamellar space following intercalation of a vermiculite by a range of cationic surfactants and followed the subsequent swelling of the organoclay compounds with several organic solvents. A single vermiculite (Eucatex) was used with three series of surfactants, N-alkyltrimethylammonium bromides, N,N'-dialkyldimethylammonium bromides, and the gemini cationic surfactants, alpha,omega-bis (N-alkyldimethylammonium) alkanes. In all cases well-defined stoichiometric compounds are obtained and the amount of surfactant intercalating the layer indicates that there are two factors controlling this amount, charge neutralization of the clay and hydrophobic packing. Packing arguments are used to deduce the fraction of non-charge-neutralizing material in the interlamellar space. It is clear that by altering the surfactant charge and structure it is possible to control the degree to which adsorption beyond charge neutralization occurs in these complexes, which is important when the capacity of such complexes to sorb other materials is considered. The general pattern of swelling of the surfactant/vermiculite complex by toluene suggests that the maximum expansion of the intralamellar space is limited by the longest chain in the surfactant. In contrast to earlier results we found that these vermiculites could be swollen by alkanes as well as aromatic solvents. This is attributed to the greater hydrophobicity of the interior of an organoclay formed from a clay of higher charge density.
Williams-Daryn
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Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ, United Kingdom.
Thomas
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RK