The phase diagram of confined fluids

The phase diagram of a Lennard-Jones fluid confined in a quenched disordered structure is studied by Grand-Canonical Monte Carlo simulation. The matrix is generated from an off-lattice diffusion-limited cluster-cluster aggregation procedure to represent a highly porous silica aerogel with a fractal structure. The Multicanonical Ensemble Sampling technique combined with the histogram reweighting method makes possible to build the liquid-vapor coexistence curve which is narrower than in the bulk. A shouldering on the liquid side of the phase diagram is observed which indicates the possibility of a second transition. Preliminary results for a larger system indicate the presence of a liquid-liquid coexistence besides the gas-liquid transition.