Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Abstract: S1.00208 : Bistable Shear-Induced Alignment and Isotropy in Nematic Cylindrical Micelles
Author:
Wormlike micelles (WLMs), such as cetyltrimethylammonium
bromide in water, are long flexible cylinders of surfactant
molecules that self-assemble as a function of concentration and
temperature. By placing a driven rheological cell into an NMR
instrument, we use ``rheo-NMR'' to correlate molecular-scale to
micron-scale details available by NMR with macroscopic
behaviors, with precise control over the sample shear rate. We
directly observe alignment of WLMs induced by shear and
magnetic field, as well as anisotropic diffusion, providing us
with a nematic phase diagram that is modulated by shear. Here
we focus on conditions where WLMs do not spontaneously field
align (at 9.4 T), but rapidly and stably field align after
application of shear. This ``bistable'' fluid persists in either
the isotropic state or the field aligned state (after shearing)
for $>$ 12 hrs. We will further describe measurements of the
nonlinear dynamics of director reorientation, with which we
quantify anisotropic elastic constants and viscosities.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.S1.208
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