Discussant: Srikanth Sastry

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Dynamical heterogeneities in Chemical gels
and attractive colloids Antonio Coniglio

• Discussant Srikanth Sastry
• JNCASR, Bangalore, India

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Outline

• Summary of main points in Antonios talk.
• What is new and interesting.
• Discussion of these in the context of glass
  formers and gel formers.

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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).

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What is new and interesting Connection between
dynamical heterogeneity and percolation

• The asymptotic (t -gt infinity, k -gt 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.

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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?
• ?

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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?

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What is new and interesting Matters of definition

• Qualitative dependence of dynamical
  susceptibility on definition via Fs(k,t) or
  overlap Q(ta).
• Unlikely to affect results in high density glassy
  systems but a caution to heed.

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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)