Poly(ethylene glycols) of molecular weights 200 to 20000 were strongly adsorbed on montmorillonite from aqueous solution. Free energies of adsorption calculated from the adsorption isotherms became more negative with increase in molecular weight and the entropy change became increasingly positive, probably due to a net desorption of water from the clay surface as the organic compound was adsorbed. The adsorption of the higher molecular weight polymers caused an increase in the interlamellar separation. The effect of the exchangeable cation on the adsorption followed the order Cs > Na > Ca > Al, indicating that the cation retained its hydration shell and did not form a direct association with the adsorbed organic molecules. Some evidence was obtained that 'water bridges' were formed between exchangeable calcium an aluminium ions and the ether groups of the polymers.
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