EFFECT OF TEMPERATURE ON THE ADSORPTION OF ORGANIC CATIONS ON CHARGED SURFACES

A study has been made of the adsorption of tetrabutylammonium nitrate (TBAN) on silver iodide and of dodecylpyridinium chloride (DPC) and dodecyltrimethylammonium bromide (DTAB) on sodium kaolinite. Our goal was to identify the Coulombic and non-Coulombic contributions to the driving force. Investigation of the temperature dependence is very suitable for that, besides studying the effects of indifferent electrolytes. All adsorption isotherms, if measured at different salt concentration, exhibit the development of a common intersection point (cip), which almost or exactly coincides with the isoelectric point. Before this point adsorption is reduced by electrolyte addition; beyond it, electrolytes promote adsorption. On the hydrophobic AgI, adsorption of TBAN proceeds until monolayer coverage, exhibiting a maximum as a function of temperature. For the amphiphilic molecules DPC and DTAB, adsorption on sodium kaolinite is not or not much dependent on temperature before the cip, whereas beyond the cip adsorption again passes through a maximum as a function of temperature. This second part is driven by hydrophobic bonding; the effect of temperature on the enthalpy shows the same trend as that for micellization of these surfactants.