Static and dynamic heterogeneities in irreversible gels and colloidal gelation

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.Comment: 9 pages, 3 figure

Metastable Water Under Pressure

We have summarized some of the recent results, including studies for bulk, confined and interfacial water. By analyzing a cell model within a mean field approximation and with Monte Carlo simulations, we have showed that all the scenarios proposed for water's P-T phase diagram may be viewed as special cases of a more general scheme. In particular, our study shows that it is the relationship between H bond strength and H bond cooperativity that governs which scenario is valid. The investigation of the properties of metastable liquid water under pressure could provide essential information that could allow us to understand the mechanisms ruling the anomalous behavior of water. This understanding could, ultimately, lead us to the explanation of the reasons why water is such an essential liquid for life