Static and dynamic heterogeneities in irreversible gels and colloidal gelation

Abstract

We compare the slow dynamics of irreversible gels, colloidal gels, glasses and spin glasses by analyzing the behavior of the so called non-linear dynamical susceptibility, a quantity usually introduced to quantitatively characterize the dynamical heterogeneities. In glasses this quantity typically grows with the time, reaches a maximum and then decreases at large time, due to the transient nature of dynamical heterogeneities and to the absence of a diverging static correlation length. We have recently shown that in irreversible gels the dynamical susceptibility is instead an increasing function of the time, as in the case of spin glasses, and tends asymptotically to the mean cluster size. On the basis of molecular dynamics simulations, we here show that in colloidal gelation where clusters are not permanent, at very low temperature and volume fractions, i.e. when the lifetime of the bonds is much larger than the structural relaxation time, the non-linear susceptibility has a behavior similar to the one of the irreversible gel, followed, at higher volume fractions, by a crossover towards the behavior of glass forming liquids.

Colloidal gels: equilibrium and non-equilibrium routes

“…In particular, in close analogy with investigations in colloidal glasses [285], recent, intense activity is aiming to characterize dynamical heterogeneities of colloidal gels. Through diffusing wave spectroscopy and time resolved correlation techniques [286,9], confocal microscopy experiments [178,287], and simulations [288,289,87], the complexity of gels emerges also in terms of different populations of slow and fast particles, which become more and more evident approaching the gel transition, and remarks a close analogy of both gel and glass transition in terms of dynamic cooperativity. Such studies are extremely useful for the establishment of a unifying theoretical framework of a (generic) dynamical arrest transition, although, again, differences are expected among the different mechanisms.…”

Growth of a dynamical correlation length in an aging superspin glass

“…self induced, disorder) and spin glasses (with quenched disorder). In a recent paper [12], Coniglio and coworkers show that in the case of quenched disorder, the dynamical susceptibility grows with lag time and reaches a plateau, whose height increases with decreasing T. The deduced dynamical correlation length is diverging at low temperature, in the same way as the static non-linear susceptibility. This behaviour is characteristic of a static phase transition.…”

Field induced anisotropic cooperativity in a magnetic colloidal glass

“…In qualitative agreement with [18,19] we report an anomalous dynamics τ (Q) in the parallel direction to the field, together with highly cooperative dynamics, due to the field-driven fluctuations of position of the NPs. This enhanced cooperativity in the direction of reduced repulsion can be compared to simulations of hard spheres where the interaction potential is tuned [33,34]. By computing numericallly χ 4 in (isotropic) colloidal hard sphere glasses and gels, Coniglio et al show that in glasses χ 4 is peaked in time, traducing the transcient nature of cooperative process, whereas in gels χ 4 reaches a plateau, traducing the persistent presence of relaxing clusters containing a large number of particles.…”