318 research outputs found
Complex dynamics in nanoscale phase separated supercooled liquids
The relaxation properties of supercooled AsxS100−x liquids are investigated using a combination of infrared
photon correlation spectroscopy and topological constraint theory. Results reveal two channels of relaxation
for sulfur-rich compositions that manifest by an unusual profile in the density-density autocorrelation function
involving two typical timescales. This indicates a reduced temperature-dependent dynamics for one of the
channels associated with a sulfur-rich segregated nanoscale phase that furthermore displays a low liquid fragility.
Conversely, the dynamics of the emerging cross-linked As-S network is associated with a growth of the
glass transition temperature with As content. These results can be quantitatively understood from topological
constraint theory applied to a phase separated network for which a dedicated constraint enumeration must be
achieved. The vanishing of this peculiar behavior occurs close to the reported isostatic reversibility window
observed at the glass transition
On the origin of the -transition in liquid Sulphur
Developing a novel experimental technique, we applied photon correlation
spectroscopy using infrared radiation in liquid Sulphur around ,
i.e. in the temperature range where an abrupt increase in viscosity by four
orders of magnitude is observed upon heating within few degrees. This allowed
us - overcoming photo-induced and absorption effects at visible wavelengths -
to reveal a chain relaxation process with characteristic time in the ms range.
These results do rehabilitate the validity of the Maxwell relation in Sulphur
from an apparent failure, allowing rationalizing the mechanical and
thermodynamic behavior of this system within a viscoelastic scenario.Comment: 5 pages, 4 eps figures, accepted in Phys. Rev. Let
High frequency dynamics in a monatomic glass
The high frequency dynamics of glassy Selenium has been studied by Inelastic
X-ray Scattering at beamline BL35XU (SPring-8). The high quality of the data
allows one to pinpoint the existence of a dispersing acoustic mode for
wavevectors () of nm, helping to clarify a previous
contradiction between experimental and numerical results. The sound velocity
shows a positive dispersion, exceeding the hydrodynamic value by 10%
at nm. The dependence of the sound attenuation
, reported for other glasses, is found to be the low- limit of a
more general law which applies also to the
higher region, where no longer holds.Comment: Phys. Rev. Lett. (Accepted
Effect of cluster size of chalcogenide glass nanocolloidal solutions on the surface morphology of spin-coated amorphous films
Amorphous chalcogenide thin film deposition can be achieved by a spin-coating
technique from proper solutions of the corresponding glass. Films produced in
this way exhibit certain grain texture, which is presumably related to the
cluster size in solution. This paper deals with the search of such a
correlation between grain size of surface morphology of as-deposited
spin-coated As33S67 chalcogenide thin films and cluster size of the glass in
butylamine solutions. Optical absorption spectroscopy and dynamic light
scattering were employed to study optical properties and cluster size
distributions in the solutions at various glass concentrations. Atomic force
microscopy is used to study the surface morphology of the surface of
as-deposited and thermally stabilized spin-coated films. Dynamic light
scattering revealed a concentration dependence of cluster size in solution.
Spectral-dependence dynamic light scattering studies showed an interesting
athermal photo-aggregation effect in the liquid state.Comment: 15 pages, 8 figure
Dynamics of proteins: Light scattering study of dilute and dense colloidal suspensions of eye lens homogenates
We report a dynamic light scattering study on protein suspensions of bovine
lens homogenates at conditions (pH and ionic strength) similar to the
physiological ones. Light scattering data were collected at two temperatures,
20 oC and 37 oC, over a wide range of concentrations from the very dilute limit
up to the dense regime approaching to the physiological lens concentration. A
comparison with experimental data from intact bovine lenses was advanced
revealing differences between dispersions and lenses at similar concentrations.
In the dilute regime two scattering entities were detected and identified with
the long-time, self-diffusion modes of alpha-crystallins and their aggregates,
which naturally exist in lens nucleus. Self-diffusion coefficients are
temperature insensitive, whereas the collective diffusion coefficient depends
strongly on temperature revealing a reduction of the net repulsive
interparticle forces with lowering temperature. While there are no rigorous
theoretical approaches on particle diffusion properties for multi-component,
non-ideal hard-sphere, polydispersed systems, as the suspensions studied here,
a discussion of the volume fraction dependence of the long-time, self-diffusion
coefficient in the context of existing theoretical approaches was undertaken.
This study is purported to provide some insight into the complex light
scattering pattern of intact lenses and the interactions between the
constituent proteins that are responsible for lens transparency. This would
lead to understand basic mechanisms of specific protein interactions that lead
to lens opacification (cataract) under pathological conditions.Comment: To appear in J. Chem. Phy
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