Effect of Chain Conformation on the Tilt Behaviour in Langmuir Monolayers

Monolayers of amphiphilic molecules at the air-water interface exhibit a phase transition from a state in which the molecules are normal to the interface to one in which they are tilted. Molecular-dynamics simulations have been used to investigate the relation between chain conformation and tilt transition, and the effect of temperature thereupon. Results show that a decrease in temperature induces an increase in tilt angle and conformational order. Monolayers at 275 and 300 K undergo a clear tilt transition at approximately 0.20 mm 2 /molecule. At high density, the tilt behaviour at equilibrium and during relaxation is coupled to the formation of gauche defects.