ELLIPSOMETRIC MODEL FOR 2-DIMENSIONAL PHASE-TRANSITION IN LANGMUIR MONOLAYERS

A microscopic ellipsometric model of dioctadecyldimethylammonium bromi de monolayer compression has been proposed. The suggested model explai ns the dependence of the ellipsometric parameters on the surface densi ty throughout the entire range of compression, comprising the liquid e xpanded (LE) and liquid condensed (LC) phases, as well as their coexis tence region. The model uses unique microscopic parameters, such as mo lecular polarizabilities, Lorentz factors and geometric molecular dime nsions. Molecules are treated as rods whose cross-section decreases li nearly during the LE-LC phase transition. During compression the rods change their orientation from parallel to the interface to almost perp endicular. It was shown that the volume density of the LE phase is 10- 15% lower than that of the LC phase. (C) 1998 Published by Elsevier Sc ience S.A.