Prof. Dr. Martin Schoen:
Ordered phases in anisometric Lennard-Jones fluids

We present Monte Carlo simulations of the isotropic-polar (IP) phase transition in an amphiphilic fluid
carried out in the isothermal-isobaric ensemble. Our model consists of Lennard-Jones spheres where the 
attractive part of the potential is modified by an orientation-dependent function. This function gives 
rise to an angle dependence of the intermolecular attractions corresponding to that characteristic of 
point dipoles. Our data show a substantial system-size dependence of the dipolar order parameter. We 
analyze the system-size dependence in terms of the order parameter distribution and a cumulant involving 
its first and second moments. The order parameter, its distribution, and susceptibility observe the 
scaling behavior characteristic of the 3D-Ising universality class. Because of this scaling behavior and
because all cumulants have a common intersection irrespective of system size we conclude that the IP 
phase transition is continuous. Considering pressures 1.3 ≤ P ≤ 3.0 we demonstrate that a line of 
continuous phase transition exists which is analogous to the Curie line in systems exhibiting a 
ferroelectric transition. Our results are qualitatively consistent with Landau’s theory of continuous 
phase transitions.