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, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
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)
[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)
About Condensed Matter lunchtime seminars
This is a weekly series of informal talks given primarily by members of the institute of condensed matter and complex systems, 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..