Short grafted chains: Monte Carlo simulations of a model for monolayers ofamphiphiles

We present Monte Carlo simulations of a coarse-grained model for Langmuir m onolayers of amphiphile molecules on a polar substrate. The molecules are m odeled as chains of Lennard-Jones beads, with one slightly larger end bead confined in a planar surface. They are simulated in continuous space under conditions of constant pressure, using a simulation box of variable size an d shape. The model exhibits a disordered phase (corresponding to the liquid expanded phase) and various ordered phases (corresponding to the condensed phases) with different types of tilt. We calculate the phase diagrams and characterize the different phases and phase transitions. The effect of vary ing the chain stiffness is also discussed.