Revised thermodynamic and dynamical properties of the hard sphere (HS) system are obtained from extensive molecular dynamics calculations carried out with large system sizes (number of particles, N) and long times.
Abstract.
We have studied the dewetting dynamics of partially wetting liquid films confined between a soft elastic hemisphere and an elastomer layer by means of systematic experiments. We focused on the experimentally most relevant case of non-axisymmetric dewetting, which initiated at the locations of minimum film thickness near the perimeter of the contact area. We found the contact line speed to be highly anisotropic in this case. It is significantly faster in the azimuthal direction along the perimeter of the contact spot than in the radially inwards direction. We developed a three-dimensional, fully coupled numerical model that reproduces many features observed in the experiments.
Graphical abstract
Micropatterned
dry adhesives rely mainly on van der Waals interactions.
In this paper, we explore the adhesion strength increase that can
be achieved by superimposing an electrostatic field through interdigitated
subsurface electrodes. Micropatterns were produced by replica molding
in silicone. The adhesion forces were characterized systematically
by means of experiments and numerical modeling. The force increased
with the square of the applied voltage for electric fields up to 800
V. For larger fields, a less-than-quadratic scaling was observed,
which is likely due to the small, field-dependent electrical conductivity
of the materials involved. The additional adhesion force was found
to be up to twice of the field-free adhesion. The results suggest
an alternative method for the controlled handling of fragile or miniaturized
objects.
In
underwater adhesion of a topographically patterned surface with
a very soft material such as human skin, the elastic deformation can
be large enough to achieve solid-on-solid contact not only on top
of the hills but also in the valleys of the substrate topography.
In this context, we have studied the dynamics of dewetting of a thin
liquid film confined between a rigid, periodic micropillar array and
a soft, elastic sphere. In our experiments, we observed two very distinct
dewetting morphologies. For large ratios of array period to micropillar
height and width, the dewetted areas tend to have a diamond-like shape
and expand with a rate similar to a flat, unpatterned substrate. When
the array period is reduced, the morphology of the dry spot becomes
irregular and its expansion rate is significantly reduced. We developed
a fully coupled numerical model of the dewetting process that reproduces
the key features observed in experiments. Moreover, we performed contact
mechanics simulations to characterize the deformation of the elastomer
and the shape of the dewetted area in a unit cell of the micropillar
array.
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