Recent
Honors Theses
Seila
Selimovic ’04
“Aging Behavior of Silica Suspensions”
Abstract:
In our study of the aging phenomena in silica suspensions we immersed precipitated
silica particles in methyl-terminated PDMS (silicone oil), mineral oil, and a
mixture of glycerol and water and measured their viscoelastic properties as a
function of time. We found that the samples based on silicone oil, initially
of a pasty consistence, became fluid-like after a period of about three weeks.
Aqueous samples aged much faster than the oily samples. We also observed that
the aging time for these samples increased with increasing volume fraction. Samples
containing mineral oil did not exhibit any changes in viscosity and elasticity.
In this paper we discuss a possible mechanism for these aging behaviors.
Publication:
"
Aging Effects in Suspensions of Silica Particles", Seila Selimovic and Yue
Hu, in Dynamics in Small Confining Systems, the Materials Research Society Symposium
Proceedings Series, ed. by J.T. Fourkas, P. Levitz, M. Urbakh, and Kathryn Wahl,
Vol. 790 (2004). Download
pdf file
" Aging
Effects of Precipitated Silica in Poly(dimethylsiloxane),” Seila
Selimovic, Sarah M. Maynard, and Yue Hu, Journal of Rheology,
51, 325-340 (2007). Download
pdf file
Stella
Offner ’03
“Three Dimensional Modeling of Electrorheological Suspensions
in a Shear Flow”
Abstract:
Electrorheological fluids are suspensions of .1 – 100 mm particles in an
insulating liquid that experiences a dramatic and reversible rheological change
when an electric field is applied. Particles form long chains parallel to the
electric field causing the viscosity of the suspension to increase by as much
as several orders of magnitude. This thesis uses Matlab computer simulations
to study electrorheological fluids under a steady shear flow. The simulations
model the behavior of the suspended particles due to varied particle size, relaxation
times, and shear flow rate. Results indicate that average stress varies substantially
as a function of the particle spinning induced by the shear flow. In addition,
for high shear and for low tilt angles, the simulations suggest that the onset
of an electric field causes the viscosity of the suspension to decrease.
Publication:
"Critical role of flow-modified permittivity in electrorheology: model and
computer simulation", Ujitha M. Dassanayake, Stella S.R. Offner*, and
Yue Hu, Phys. Rev. E, 69, 021507 (2004). Download
pdf file |
