Order and chaos in soft condensed matter
A K
SOOD and RAJESH GANAPATHY
Department of Physics, Indian Institute of Science,
E-mail: asood@physics.iisc.ernet.in
Abstract. Soft
matter, like
colloidal suspensions and surfactant
gels, exhibit strong response to
modest external perturbations. This
paper reviews our recent
experiments on the nonlinear flow behaviour
of surfactant worm-like micellar gels. A rich dynamic behaviour
exhibiting regular, quasi-periodic,
intermittency and chaos is
observed. In particular, we have
shown experimentally that the route
to chaos is via Type-II
intermittency in shear thinning worm-like
micellar
solution of cetyltrimethylammonium tosylate where the
strength of flow-concentration
coupling is tuned by the addition of
sodium chloride. A Poincar\'e first
return map of the time series
and the probability distribution of
laminar length between burst
events show that our data are
consistent with Type-II intermittency.
The existence of a `Butterfly' intensity pattern in small
angle light
scattering (SALS) measurements
performed simultaneously with the
rheological
measurements confirms the coupling of flow to
concentration fluctuations in the
system under study. The scattered
depolarised
intensity in SALS, sensitive to orientational order
fluctuations, shows the same
time-dependence (like intermittency) as
that of shear stress.
Keywords. Surfactants; stress relaxation; flow
instabilities; rheo-optics.
PACS Nos 82.70.Uv; 83.85.St; 83.85.Ei; 82.70.Gg; 83.60.Wc