Shear induced gelation of micelles -- A ring-driven thing?

Condensed Matter lunchtime seminar

Shear induced gelation of micelles -- A ring-driven thing?

  • Event time: 1:00pm
  • Event date: 13th November 2000
  • Speaker: Mike Cates (Formerly School of Physics & Astronomy, University of Edinburgh)
  • Location: Room 2511,

Event details

Many types of surfactant in water form long, flexible, chainlike micelles which can entangle to form a viscoelastic state. This state is now fairly well understood: it has a characteristic relaxation time (the Maxwell time) whose dependence on system parameters agrees with theory, and it shows shear thinning when the shear rate is large compared to the inverse Maxwell time (also as predicted) [1]. However, in one class of systems (salt free ionic surfactants) there is a regime just below the entanglement threshold which shows shear thickening instead. This bizarre behaviour has remained unexplained ever since it was first discovered about 20 years ago. Very recent experiments confirm that the state has some unidentified degrees of freedom which relax much more slowly than the Maxwell time [2]. A tentative explanation for the shear thickening regime and its exotic properties will be outlined.
[1] M. E. Cates and S. J. Candau, J. Phys. Cond. Mat. 2, 6869 (1990)
[2] See e.g. J.-F. Berret et al., Eur. Phys. J. E 2, 343 (2000)

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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