Incollection,
Order disorder transition in a model of colloidal particles
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)
Abstract
An interesting feature of colloidal suspensions is
that the interaction between particles can be well controlled.
In fact particles can be coated and stabilized
leading to a hard sphere behavior, an attractive depletion
interaction can be brought out by adding some nonadsorbing
polymers, and finally a net charge on the surface gives
rise to a long-range electrostatic repulsion.
The competition between such attractive and repulsive interactions
produces a rich phenomenology both in the structure and in the dynamics.
For particular choices of the interaction parameters,
the aggregation of particles is favored but the liquid-gas
phase transition can be avoided and the cluster size can be
stabilized at an optimum value. On increasing the volume fraction,
the system undergoes a percolation transition, transforming into a
nonergodic disordered gel, where structural arrest occurs.
Using Molecular Dynamics we showed that, for our choice of the interaction
parameters, such phase is a metastable one,
and eventually the system spontaneusly orders, to form a periodic
structure composed of parallel columns of particles. We then study the phase diagram of the system, by evaluating the free energy of the disordered and ordered phases, and find the region where the columnar phase is the
stable one. Such phases are rarely seen in experiments due to the presence
of a little polydispersity in the particles, that makes nucleation times
much longer. We also find that at still higher volume fractions the stable
phase is a lamellar one.
