On clay minerals and new insights in hydrophobic interactions

J. Lyklema

Wageningen Agricultural University, Department of Physical and Colloid Chemistry, Deijenplein 6, 6708 HB Wageningen, The Netherlands

Abstract The adsorption of dodecylpyridinium chloride and dodecyltrimethylammonium bromide on Na-kaolinite is investigated by studying the effect of electrolyte and temperature on the adsorption, by means of electrophoresis and microcalorimetry. A sharp distinction between adsorption in the first and second layer is observed. The point where these two regions meet is retrieved in all experiments. Second layer adsorption is driven by hydrophobic bonding, for which the enthalpy is now established as a function of temperature. It changes from endothermic at low temperature to exothermic at higher temperature. A new molecular interpretation for hydrophobic bonding is proposed, based on quasichemical lattice statistics with orientation-dependent interactions. All experimental features can at least semiquantitatively be explained by this new model.

Key words Adsorption — surfactants — clay minerals — hydrophobic bonding

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