Next: References
Research profile
From daily experience, liquids are well-known to everybody. Besides water,
which certainly represents the most prominent example, there
is a huge variety of liquids with distinctive properties employed
for special purposes such as cooling engines or tarring roads, dilution,
lubrification, hydraulics, automatic transmissions, or glass fiber optics etc.
In the search for new materials, liquids of an extremely high viscosity --ie
glasses-- have attracted much attention, recently. It turns out that our
knowledge is still poor of how an amorphous solid (glass)
forms from a high-density fluid (liquid). Although people have been able
to produce silicon-oxide glass bowls for more
than 5000 years, they failed to understand the mechanism behind the
liquid-to-glass transition. Why does a liquid show this dramatic increase of
viscosity upon supercooling?
Thorough understanding of those dynamical processes which govern the
transport properties --eg the viscosity-- of a liquid
is, however, indispensable for developing new amorphous materials tailored
to the needs of their prospective applications.
This implies the general aim of our current research: we intend to contribute
to a better understanding of the relaxation mechanism(s) responsible for the
dynamical properties of supercooled liquids and the glass transition.
In the following you will find a selection of results obtained lately.
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We discussed the motion of a particle moving through the voids of a glassy
matrix and calculated the spatial correlation function of random-potential
fluctuations
to which the particle is exposed. Usually, in a disordered system, lacking
more accurate information, one simply assumes a Gaussian correlation of
potential fluctuations. In our work we
showed that the potential fluctuations as a function of wavenumber are
strongly non-Gaussian and definitely reflect the static structure of the
glassy matrix.[BGK94]
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For a binary mixture of disparate-size neutral particles we calculated the
partial-density relaxation functions within a mode-coupling
approximation, which, we believe, gives a good description of the
nonlinear dynamical feedback processes
dominating the relaxation of density fluctuations in the supercooled phase.
We find a glass transition at a critical packing fraction
in connection with the localization of the large particles, only.
The small spheres enter a delocalized phase. They move in an almost static
random potential produced by the large particles. At a critical packing
fraction , the random-potential fluctuations are sufficiently
large to localize the small particles within the glass. [KB95]
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Frequency-dependent self-diffusion coefficients
for both particle species of a supercooled binary hard-sphere liquid
have been calculated within
a mode-coupling approximation.
It is found that a small bump appears in of the small
particles at low frequencies when the glass transition is
approached. This is interpreted as the onset of a change in the
diffusion mechanism of the small particles. When the glass is formed,
the small-particle diffusion changes from fast liquid-like diffusion
to a slower motion (``anomalous diffusion'') in a random
potential.[BK95]
-
The long-time limits of the density-relaxation functions (non-ergodicity
parameters) of a supercooled ionic melt, a symmetric molten salt (SMS),
have been calculated within a mode-coupling approach. From the
non-ergodicity parameters the wavenumber-dependent static dielectric
function for an ionic glass was deduced.[Sed95]
Please, refer to section Recent Publications for more references.
Next: References
Juergen Bosse
Sun Feb 2 18:51:37 MET 1997