Studies in Physico-chemical Properties of Caseins: Part VI. Selective Adsorption from Binary Solutions on Caseins

Department of Chemistry, Panjab University, Chandigarh. 160014

Manuscript received 13 September 1972; revised 12 February 1973; accepted 7 April 1973

Adsorption of water and methanol vapours on caseins isolated from milk by different methods is a physical and reversible process. There appears to be no evidence for chemisorption of any portion of the adsorbed vapours. The adsorption of these vapours takes place on the hydrophilic portion of the surface constituted by the presence of polar groups and, therefore, measures only the hydrophilic portion of the surface. The rest of the surface, constituted by the hydrophobic residues of the amino acids, escapes measurements. The composite adsorption isotherms of binary liquid solutions of methanol and benzene as well as methanol and carbon tetrachloride are V-shaped indicating strong preference for methanol in each case. The composite isotherms of binary solutions of benzene and \(n\)-heptane, in which both the components are non polar, are typical S-shaped indicating that there is no exclusive preference for any of the components. The extrapolation of the linear section of any one of the isotherms gives intercepts on the ordinates which define the composition of the adsorbed phase in the monolayer from which the total surface of the caseins including hydrophilic and hydrophobic portions, can be evaluated.