157 research outputs found
Single particles accelerate final stages of capillary break up
Droplet formation of suspensions is present in many industrial and
technological processes such as coating and food engineering. Whilst the finite
time singularity of the minimum neck diameter in capillary break-up of simple
liquids can be described by well known self-similarity solutions, the pinching
of non-Brownian suspension depends in a complex way on the particle dynamics in
the thinning thread. Here we focus on the very dilute regime where the filament
contains only isolated beads to identify the physical mechanisms leading to the
pronounced acceleration of the filament thinning observed. This accelerated
regime is characterized by an asymmetric shape of the filament with an enhanced
curvature that depends on the size and the spatial distribution of the
particles within the capillary thread.Comment: accepted for Europhysics Letter
Quantitative analysis of the debonding structure of soft adhesives
We experimentally investigate the growth dynamics of cavities nucleating
during the first stages of debonding of three different model adhesives. The
material properties of these adhesives range from a more liquid-like material
to a soft viscoelastic solid and are carefully characterized by small strain
oscillatory shear rheology as well as large strain uniaxial extension. The
debonding experiments are performed on a probe tack set-up. Using high contrast
images of the debonding process and precise image analysis tools we quantify
the total projected area of the cavities, the average cavity shape and growth
rate and link these observations to the material properties. These measurements
are then used to access corrected effective stress and strain curves that can
be directly compared to the results from the uniaxial extension
Serpentine channels: micro -- rheometers for fluid relaxation times
We propose a novel device capable of measuring the relaxation time of
viscoelastic fluids as small as 1\,ms. In contrast to most rheometers, which by
their very nature are concerned with producing viscometric or
nearly-viscometric flows, here we make use of an elastic instability which
occurs in the flow of viscoelastic fluids with curved streamlines. To calibrate
the rheometer we combine simple scaling arguments with relaxation times
obtained from first normal-stress difference data measured in a classical shear
rheometer. As an additional check we also compare these relaxation times to
those obtained from Zimm theory and good agreement is observed. Once
calibrated, we show how the serpentine rheometer can be used to access smaller
polymer concentrations and lower solvent viscosities where classical
measurements become difficult or impossible to use due to inertial and/or
resolution limitations. In the absence of calibration the serpentine channel
can still be a very useful comparative or index device.Comment: accepted for for publication in Lab on a chi
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