Thermodynamic study on phase transition in adsorbed film of fluoroalkanol at the hexane/water interface. 7. Pressure effect on the miscibility in theadsorbed film of alkanol and fluoroalkanol mixture

The Miscibility of 1-icosanol (C20OH) and 1,1,2,2-tetrahydroheptadecafluoro decanol (FC10OH) in the adsorbed film at the hexane/water interface was stu died by measuring the pressure dependence of interfacial tension at various compositions and analyzing the experimental results thermodynamically. The criterion of ideal mixing in the adsorbed film with respect to the volume of adsorption Delta(w)(H)upsilon was constructed and used to examine the HV value deviates nonideal mixing of C20OH and FC10OH in the adsorbed film. I t is found that the Delta(w)(H)upsilon positively from the ideal mixing lin e, and therefore the mixing of C20OH and FC10OH molecules causes a larger i ncrease in volume in the adsorbed film than in the bulk solution. Furthermo re, the excess volume of adsorption upsilon(H,E) was positive and its magni tude was comparable to that of the liquid alkane and perfluoroalkane mixtur e. This result is probably due to the increase in the occupied area of indi vidual components at the interface. To gain a better understanding of the m iscibility of C20OH and FC10OH in the adsorbed film, the phase diagram of a dsorption (PDA) was constructed at various pressures. We found that these a lcohol molecules become less miscible and therefore the activity coefficien ts of alcohols become larger in the expanded state with increasing pressure . This is in accord with the positive upsilon(H,E) value, Furthermore the C 20OH and FC10OH molecules were practically immiscible in the condensed stat e at high pressure.