Microphase separation in mixtures of Lennard-Jones particles

Several binary systems composed of one-centre Lennard-Jones particles with identical size and interaction parameters, sigma(11), sigma(22), epsilon(11), epsilon(22) and epsilon(12), but different cross diameter parameters sigma(12), were simulated using an extended version of the Gibbs ensemble Monte Carlo method, in an attempt to predict the fluid phase behaviour in such systems. No liquid-liquid phase separation was found in the mixtures but all cases studied exhibit a structured liquid phase in equilibrium with its vapour. The domain shapes and patterns observed both in three- and two-dimensional simulations (stripe and bubble phases) were interpreted within the framework of the phenomenology of modulated phases, also known as microphase separated fluids. The appearance of stripe patterns occurs when sigma(12) is larger than sigma(11), while the bubble phases are characteristic of systems with sigma(12) smaller than sigma(11).