C. Buzano et Lr. Evangelista, THE PHASE-TRANSITION IN AMPHIPHILIC MONOLAYERS - ISOTHERMS IN THE CLUSTER VARIATION METHOD, Journal of physics. Condensed matter, 6(28), 1994, pp. 5323-5334
The liquid-expanded (LE)-liquid-condensed (LC) phase transition in mon
olayers of amphiphilic molecules is investigated in the pair approxima
tion of the cluster variation method. The model analysed is the model
proposed by Firpo et al which can be mapped into the Blume-Emery-Griff
iths Hamiltonian. The signatures of the LE-LC transition are searched
for as break points on the isotherms of the surface pressure-molecular
area diagram. The results obtained in the pair approximation are impr
oved with respect to those obtained in the Bragg-Williams approximatio
n for a set of typical energy and entropy parameters in the case of pe
ntadecanoic acid. In particular, the LE-LC phase transition is shown t
o be weakly first order. A comparison with experimental results gives
satisfactory agreement.