Discussant: Srikanth SastryJNCASR, Bangalore, India

Dynamical heterogeneities in Chemical gels Dynamical heterogeneities in Chemical gels and attractive colloidsand attractive colloids

Antonio ConiglioAntonio Coniglio

• Summary of main points in Antonio’s talk.

• What is new and interesting.

• Discussion of these in the context of glass formers and gel formers.

OutlineOutline

Systems of interest: Chemical and colloidal gels

Model systems: i. LJ + FENE bonds (chemical gel),

ii. DLVO (colloidal gel)

Phenomenon: Dynamical heterogeneity

Chemical gels: • in the limit of large time mean cluster size of

percolation. • k dependence of yields percolation exponents.

Colloids: • given by the mean cluster size of mobile

particles. • Differences in the behavior of depending on

definition (Fs(k,t) vs. overlap Q).

Summary of resultsSummary of results

• The asymptotic (t -> infinity, k -> 0) value of gives the mean size of percolation clusters.

as(k) gives additional information about the structure of percolation clusters.

• In this case, dynamical heterogeneity is understood from geometry.

• Looking at dynamical heterogeneity offers a way of obtaining geometric information.

•

What is new and interesting: Connection between What is new and interesting: Connection between dynamical heterogeneity and percolation dynamical heterogeneity and percolation

• Is dynamical heterogeneity that arises from structural heterogeneity interesting?

• In “attractive glasses”, gels etc, aspects of bonding and connectivity play a definite role, so has to be taken into account.

• Are there circumstances where looking at

dynamical heterogeneity would be a relevant approach to getting information on structure?

• ?

What is new and interesting: Connection between What is new and interesting: Connection between dynamical heterogeneity and percolation: Questions dynamical heterogeneity and percolation: Questions

• Description of dynamics in terms of the size dependent mobility of clusters.

• Useful in the case of transient clusters?

What is new and interesting: Describing dynamics What is new and interesting: Describing dynamics

• Qualitative dependence of dynamical susceptibility on definition via Fs(k,t) or overlap Q(t;a).

• Unlikely to affect results in high density glassy systems but a caution to heed.

What is new and interesting: Matters of What is new and interesting: Matters of definitiondefinition

• For transient bonds, dynamical susceptibility related to mean cluster size of mobile particles.

• At high densities, “excess” heterogeneity indicative of crossover in dynamics?

• But mean cluster size captures peak value in both cases.

• ?• It will be interesting to study this

relation in gel other models, with tunable bond life times ec (Hurtado, Chaudhuri, Berthier, Kob; Saw, Kob, Sastry; Del Gado, Kob)

What is new and interesting: Transient bonds What is new and interesting: Transient bonds