Thermodynamics of adsorption of O-n-dodecylpentaethylene glycol from aqueous solution on to carbon and silica at 313 K

Abstract

Adsorption isotherms and enthalpies of adsorption from an aqueous solution of O-n-dodecylpentaethylene glycol on to graphitised carbon and silica at 313 K are reported. Adsorption on carbon initially gives a monolayer in which n-dodecyl chains interact with, but are also partially lifted from the surface and pentaethylene glycol chains protrude from the surface at saturation coverage to form a structured E₅/water layer in the interfacial region. At higher C₁₂E₅ concentrations in solution, further adsorption led to the formation of multilayers likened to a surface-nucleated liquidcrystalline lamellar phase. Adsorption on silica led to monolayer formation followed by bilayer formation. Interactions between surface silanol groups and E₅ chains governed the mean area occupied by each C₁₂E₅ molecule in the first layer of the bilayer and this in turn determined the distribution of C₁₂E₅ in the second layer. The results are compared with previous isotherm and enthalpy data for the same systems at 298 K.