Incollection,
Modelling colloidal suspensions: Gelation, network formation and phase separation.
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)
Abstract
In colloidal gels, the deep connection existing between their unusual
dynamics and the open network
characterizing their structure is still not understood.
In the dramatic slowing down of the dynamics
accompanying the gel formation, the experimental findings suggest that
different relaxation mechanisms interplay at a microscopic level,
which have not been elucidated yet. Moreover, in colloidal suspensions
at low volume fractions the underlying thermodynamics may significantly
interplay and/or compete with gel formation via phase separation processes.
I will review some recent developments based on molecular
dynamics simulations of model systems. In particular I will illustrate
the case of a colloidal suspension with competing attraction and repulsion, where gelation results to be directly coupled to microphase separation.
Then I will discuss a model in which directional interactions
are able to produce a persistent gel network at relatively high
temperatures, where phase separation does not occur, without
imposing a local functionality of the meso-particle. The numerical study shows in this case that the formation of the gel network does induce a non-trivial length scale dependence of the dynamics in a simple model for colloidal gels: In the incipient gel, the relaxation at high wave vectors is due to the fast cooperative motion of pieces of the gel structure, whereas at low wave vectors the overall rearrangements of the heterogeneous gel make the system relax via a stretched exponential decay of the time correlators. The coexistence of such diverse relaxation mechanisms is determined by the formation of the gel network
(i.e. the onset of the elastic response of the system) and it is characterized
by a typical crossover length which is of the order of the network mesh size.
