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

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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.

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