Irreversible Aging Dynamics and Phase Behavior of Aqueous Suspensions of Laponite

Condensed Matter lunchtime seminar

Irreversible Aging Dynamics and Phase Behavior of Aqueous Suspensions of Laponite

  • Event time: 1:00pm
  • Event date: 7th June 2010
  • Speaker: Yogesh M. Joshi (Department of Chemical Engineering Indian Institute of Technology Kanpur)
  • Location: Room 2511,

Event details

In this talk, we will discuss an aging behavior of aqueous suspension of Laponite with varying concentration of NaCl using rheological tools. Laponite is synthetic layered silicate clay with individual particle having a disc like shape. In an aqueous media, particle has permanent negative charge on its surface while the charge on its edge depends on pH of the medium. Aqueous suspension of Laponite undergoes enhancement in elastic modulus and viscosity with time and demonstrates various characteristic features of soft glassy materials. In rheological experiments we observe inherent irreversibility in the aging dynamics which forces the system not to rejuvenate to the same state in the shear melting experiment carried out at a later date since preparation. The extensive rheological experiments carried out as a function of time elapsed since preparation and temperature demonstrate a self-similar trend in the aging behavior irrespective of the concentration of salt. We observe that an exploration of the low-energy states as a function of aging time is only kinetically affected by the presence of salt. We estimate that the energy barrier to attain the low-energy states decreases linearly with increase in the concentration of salt. The observed superposition of all the elapsed time, and the salt-concentration-dependent data suggests that the aging which occurs in low salt concentration systems over a very long period is qualitatively similar to the aging behavior observed in systems with high salt concentration over a shorter period. The observed behavior suggests formation of edge to surface aggregates. We will conclude by discussing various controversies associated with aqueous suspension of Laponite and our views on the same.

This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..

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