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Discussant: Srikanth Sastry JNCASR, Bangalore, India

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

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Discussant: Srikanth Sastry JNCASR, Bangalore, India

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  1. 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. 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)

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