1. Discussant: Srikanth Sastry JNCASR, Bangalore, India
Dynamical heterogeneities in Chemical gels and attractive colloids
Antonio Coniglio
Discussant: Srikanth Sastry
JNCASR, Bangalore, India

2. Outline 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.

3. Summary of results 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).

4. In this case, dynamical heterogeneity is understood from geometry.
What is new and interesting: Connection between dynamical heterogeneity and percolation
The asymptotic (t -> infinity, k -> 0) value of c4 gives the mean size of percolation clusters.
cas(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.

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

6. What is new and interesting: Describing dynamics
Description of dynamics in terms of the size dependent mobility of clusters.
Useful in the case of transient clusters?

7. What is new and interesting: Matters of definition
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.

8. What is new and interesting: Transient bonds
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)