Past Seminars Seminários Já Decorridos 2009

My name is bonding: self assembly and phase transitions

By: Jose Maria Castro Tavares
From: CFTC
At: Complexo Interdisciplinar, Anfiteatro
[2009-03-18] 12:00

We investigate the influence of strongly directional, or bonding, interactions on the phase diagram of complex fluids. To this end, we generalize a simple model consisting of particles interacting through a hard core repulsion and short ranged attractive bonding sites. We will start by considering a 2-dimensional lattice version with two bonding sites and show that, although the liquid vapor condensation is absent, an isotropic nematic phase transition of the self assembled chains occurs. This transition is fully characterized, both by the results of Monte Carlo simulations and by mean field theory, and we conclude that the isotropic nematic transition enhances bonding. Finally, we investigate the case of 3 bonding sites, two equal (A) and one different (B). Using Wertheim theory, we calculate the phase diagrams for the whole range of bonding energies. In the case where the AA bonding energy is much larger than the AB and the BB bonding energies, long chains (with AA bonds) are formed. We establish analytically the conditions under which these chains can condensate, and relate the liquid vapor phase transition to the underlying structure of self assembled clusters.