10 research outputs found
A temperature-controlled device for volumetric measurements of Helium adsorption in porous media
We describe a set-up for studying adsorption of helium in silica aerogels,
where the adsorbed amount is easily and precisely controlled by varying the
temperature of a gas reservoir between 80 K and 180 K. We present validation
experiments and a first application to aerogels. This device is well adapted to
study hysteresis, relaxation, and metastable states in the adsorption and
desorption of fluids in porous media
Effects of Pore Walls and Randomness on Phase Transitions in Porous Media
We study spin models within the mean field approximation to elucidate the
topology of the phase diagrams of systems modeling the liquid-vapor transition
and the separation of He--He mixtures in periodic porous media. These
topologies are found to be identical to those of the corresponding random field
and random anisotropy spin systems with a bimodal distribution of the
randomness. Our results suggest that the presence of walls (periodic or
otherwise) are a key factor determining the nature of the phase diagram in
porous media.Comment: REVTeX, 11 eps figures, to appear in Phys. Rev.
Local mean-field study of capillary condensation in silica aerogels
We apply local mean-field (i.e. density functional) theory to a lattice model
of a fluid in contact with a dilute, disordered gel network. The gel structure
is described by a diffusion-limited cluster aggregation model. We focus on the
influence of porosity on both the hysteretic and the equilibrium behavior of
the fluid as one varies the chemical potential at low temperature. We show that
the shape of the hysteresis loop changes from smooth to rectangular as the
porosity increases and that this change is associated to disorder-induced
out-of-equilibrium phase transitions that differ on adsorption and on
desorption. Our results provide insight in the behavior of He in silica
aerogels.Comment: 19 figure
Dynamical Scaling: the Two-Dimensional XY Model Following a Quench
To sensitively test scaling in the 2D XY model quenched from
high-temperatures into the ordered phase, we study the difference between
measured correlations and the (scaling) results of a Gaussian-closure
approximation. We also directly compare various length-scales. All of our
results are consistent with dynamical scaling and an asymptotic growth law , though with a time-scale that depends on the
length-scale in question. We then reconstruct correlations from the
minimal-energy configuration consistent with the vortex positions, and find
them significantly different from the ``natural'' correlations --- though both
scale with . This indicates that both topological (vortex) and
non-topological (``spin-wave'') contributions to correlations are relevant
arbitrarily late after the quench. We also present a consistent definition of
dynamical scaling applicable more generally, and emphasize how to generalize
our approach to other quenched systems where dynamical scaling is in question.
Our approach directly applies to planar liquid-crystal systems.Comment: 10 pages, 10 figure
Development of potential antiviral strategy against coxsackievirus B4
10.1016/j.virusres.2010.02.017Virus Research1501-285-9
Multispeckle diffusing wave spectroscopy of colloidal particles suspended in a random packing of glass spheres
We use a multispeckle diffusing wave spectroscopy (MSDWS) method to study the ensemble-averaged dynamics of the fluctuating speckle pattern when illuminating colloidal particles suspended in a static and opaque porous medium with a coherent light source. Experiments were performed with Brownian latex particles in a random packing of glass spheres. The mixing of the light scattered by the moving colloidal particles and the porous matrix gives rise to a plateau value of the intensity autocorrelation function in the long-waiting-time limit. From the plateau in the correlation function, we can determine the fraction of light scattered from moving particles and estimate the photon mean free path in the colloidal solution. The method opens up promising possibilities to probe the static fraction in semisolid material