MOLECULAR-DYNAMICS SIMULATIONS OF LANGMUIR-BLODGETT MONOLAYERS WITH EXPLICIT HEADGROUP INTERACTIONS

Energy minimisation and molecular dynamics calculations have been perf ormed for models of Langmuir-Blodgett films containing stearic acid mo lecules. The model includes a specific representation of the atoms and dipole moment of the carboxylic acid head-group. Simulations have bee n performed at head-group areas per molecule of 20.6 angstrom2 and 21. 2 angstrom2 at room temperature. This all-atom model predicts signific ant conformational disorder at the torsional angle connecting the head -group to the hydrocarbon chain. The strong charge/image-charge intera ction doubles the tilt of the layer over that found for the united-ato m Lennard-Jones head-group. The dipoles of the head-group are aligned parallel to the surface forming a two sub-lattice structure in the pla ne of the surface.