Study of Aging in
Colloidal Glass-formers
(KZ Win)
We are involved in collaborative studies on the structural and
rheological studies of colloids on crossing the glass transition
concentration. We take the alpha relaxation time of colloids obtained
in multi-speckle diffusive wave spectroscopy (DWS) as a measure of
structure and keep track of it as a function of aging time. In
collaboration with Tetsuharu Narita and Francois Lequeux of ESPCI,
Paris, France, we have built a DWS system at Texas Tech. The figure is
the evolution of the intensity auto-correlation function as the aging
time increases showing that the characteristic time increases with aging
time. One of the questions we would like to answer is how far one can
push the analogy between conventional glass formers like polymers and
colloidal glasses.
The experiments we perform involve changing the colloidal concentration
rapidly similar to changing temperature in a molecular glass and to that
end we are using two different techniques. In the first technique, we
use thermosensitive polymer particles suspended in water. By changing
temperature, we effectively change its concentration which is analogous
to the temperature in conventional glass formers. The figure shows the
aging response of such a thermosensitive particle suspension after a
temperature down-jump that corresponds to a concentration change from
below to above the glass concentration; more complicated history are
been performed as well. These particles are synthesized for us by
Srinivas Pullela and Zhengdong Cheng at Texas A&M University. We have
also built a high pressure light scattering cell to change the
concentration of silica suspension by applying pressure. Results are
anticipated to provide fundamental information related to the glass
transition event.
Funding: Vice President for
Research at Texas Tech University
The John R. Bradford Endowment at Texas Tech
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Nonlinear Rheology of Colloidal Suspensions
(Nabila
Shamim)
The rheological properties of colloidal suspensions were studied
with an Advanced Rheometric Expansion System (ARES). We are
investigating the dynamic responses of Si nanoparticles in ionic
liquids. Linear and nonlinear rheological properties as a
function of particle concentration and size are being
investigated.
Synthesis
Spherical silica nanoparticles were synthesized in our
laboratory from aqueous alcohol solutions of silicon alkoxides
in the presence of ammonia as a catalyst by using sol-gel
process.
Figure1: 280 nm diameter SiO2 particle as imaged
by TEM
Figure2:
Particle size distribution from dynamic light scattering of the
same SiO2 particle as shown in Fig 1.
Funding:
Petroleum research fund
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