Molecular dynamics simulation of domain formation in Langmuir monolayers of molecules with dipole moments

Abstract

A two-dimensional molecular dynamics model of dimers and monomers with in-plane and off-plane dipole moments is set up in order to test the importance of different anisotropic forces on the creations of pinned labyrinthine-like domains, observed in monolayers. The model is designed especially in such a way as to simulate the domain growth in Langmuir monolayers of diglycerides or phospholipids. The simulations show that in-plane dipole moments only have a minor impact on the domain growth, whereas the off-plane dipole moments inhibit the domain formation. The dimers align for big values of the off-plane dipole moment and maintain in a pinned, non-equilibrium conformation. For smaller values of the off-plane dipole moments the mean size of the phases grow algebraically, R(t) = at ⁿ ; but slower than in the case of no dipole moment. This behaviour is explained by that the created interfaces constitute a strong and repulsive field which slows down the phase separation.