This project has been cancelled. The intention of these
NASA-sponsored experiments was to study colloidal suspensions
in microgravity conditions, on
the International Space Station. Our particular question
was the behavior of binary colloidal glasses in microgravity.
Glasses show aging behavior: their properties slowly change
over time, which we have been
studying already on Earth. Our objectives
for the microgravity studies were:
Study the influence of microgravity on colloidal
glasses. NASA's previous two microgravity studies
of monodisperse colloidal glasses were thwarted by unexpected
difficulties with crystallization. We planned to study a mixture
of two sizes of particles, choosing the sizes and relative
concentrations to prevent crystallization. This would
highlight differences between colloidal glasses on Earth
and in microgravity that were previously masked by the
microgravity-related crystallization.
Study heterogeneous dynamics in an aging system
over a much longer range of time scales than previously
accessible. Earth-based experiments are inherently
limited by sedimentation effects; invariably the sample begins
to change due to sedimentation before long time scales are
reached. It is precisely the asymptotic, long-time behavior
that is most interesting in studies of aging.
Clarify similarities and differences of aging
materials. Our current work (at Emory) focused on
monodisperse colloidal glasses on Earth, and Dr. Cipelletti's
work has studied colloidal gels. This proposal extended these
studies to binary hard sphere samples.