PHASE-TRANSITIONS IN DENSE LIPID MONOLAYERS GRAFTED TO A SURFACE - MONTE-CARLO INVESTIGATION OF A COARSE-GRAINED OFF-LATTICE MODEL

Semiflexible amphiphilic molecules end-grafted at a flat surface are m odeled by a bead-spring chain with stiff bond angle potentials. Consta nt density Monte Carlo simulations are performed varying temperature, density, and chain length of the molecules, whose effective monomers i nteract with Lennard-Jones potentials. For not too large densities and low temperatures the monolayer is in a quasi-two-dimensional crystall ine state, characterized by uniform tilt of the (stretched) chains. Ra ising the temperature causes a second-order transition into a (still s olid) phase with no tilt. For the first time, finite size scaling conc epts are applied to a model of a surfactant monolayer, and it is found that the technique in this case again is useful to locate the transit ion more precisely. For comparison, also a one-dimensional version of the model is studied, and directions for future extensions of this mod eling are discussed.