Route
to Rheochaos in Nonlinear Flow of Surfactant Gels.
Department of
Physics, Indian Institute of Science,
The nonlinear flow behaviour of a viscoelastic gel formed due to entangled cylindrical worm-like micelles of the surfactant CTAT shows rheochaos [1, 2]: for a suitable range of concentrations and temperatures, the stress vs shear-rate curve shows a plateau signaling a rheological phase coexistence and, in the plateau region, the time series of the shear and normal stresses at constant shear rate show deterministic chaos. Recently [3] we have shown experimentally that the route to chaos is via intermittency in the CTAT gels where the strength of flow-concentration coupling is tuned by the additional of salt. A Poincare first return map of the time series and the probability distribution of laminar lengths between burst events shows that our data is consistent with type-II intermittency. The coupling of flow to concentration fluctuations is evidenced by the Butterfly intensity pattern in Small Angle Light Scattering (SALS) measurements performed simultaneously with the rheological measurements. The scattered depolarised intensity in SALS, sensitive to orientational order fluctuations, shows the same time-dependence (like intermittency) as that of shear stress. We will also present our recent experiments when shear stress is kept constant. Attempts to understand rheochaos in our theoretical model will also be presented [4,5].
[1] R. Bandyopadhyay, G. Basappa, and A. K. Sood, Phys.
Rev. Lett. 84, 2022 (2000).
[2] R. Bandyopadhyay and A. K. Sood, Europhys. Lett. 56, 447 (2001).
[3] R. Ganapathy and A. K. Sood, Intermittency route to rheochaos
in wormlike micelles with flow-concentration coupling, To
appear in Phys. Rev. Lett. (2006).
[4] B. Chakrabarti, M. Das, C. Dasgupta, S. Ramaswamy and A. K. Sood, Spatiotemporal rheochaos in
nematic hydrodynamics, Phys. Rev. Lett. 92, 55501-1 (2004).
[5] M. Das, B. Chakrabarti, S. Ramaswamy and A. K. Sood, Routes
to spatio-temporal chaos in the rheology of nematogenic fluids, Phys.Rev.E
71, 021707(2005).