321 research outputs found
Note and calculations concerning elastic dilatancy in 2D glass-glass liquid foams
When deformed, liquid foams tend to raise their liquid contents like immersed
granular materials, a phenomenon called dilatancy. We have aready described a
geometrical interpretation of elastic dilatancy in 3D foams and in very dry
foams squeezed between two solid plates (2D GG foams). Here, we complement this
work in the regime of less dry 2D GG foams. In particular, we highlight the
relatively strong dilatancy effects expected in the regime where we have
predicted rapid Plateau border variations.Comment: 12 pages, 3 tables, 5 figure
Proposal to reject Illicium san-ki Perr., a threat to Clausena anisumolens (Blanco) Merr. (Rutaceae)
Non-linear oscillatory rheological properties of a generic continuum foam model: comparison with experiments and shear-banding predictions
The occurence of shear bands in a complex fluid is generally understood as
resulting from a structural evolution of the material under shear, which leads
(from a theoretical perspective) to a non-monotonic stationnary flow curve
related to the coexistence of different states of the material under shear. In
this paper we present a scenario for shear-banding in a particular class of
complex fluids, namely foams and concentrated emulsions, which differs from
other scenarii in two important ways. First, the appearance of shear bands is
shown to be possible both without any intrinsic physical evolution of the
material (e.g. via a parameter coupled to the flow such as concentration or
entanglements) and without any finite critical shear rate below which the flow
does not remain stationary and homogeneous. Secondly, the appearance of shear
bands depends on the initial conditions, i.e., the preparation of the material.
In other words, it is history dependent. This behaviour relies on the tensorial
character of the underlying model (2D or 3D) and is triggered by an initially
inhomogeneous strain distribution in the material. The shear rate displays a
discontinuity at the band boundary, whose amplitude is history dependent and
thus depends on the sample preparation.Comment: 18 pages - 17 figure
Velocity profiles in shear-banding wormlike micelles
Using Dynamic Light Scattering in heterodyne mode, we measure velocity
profiles in a much studied system of wormlike micelles (CPCl/NaSal) known to
exhibit both shear-banding and stress plateau behavior. Our data provide
evidence for the simplest shear-banding scenario, according to which the
effective viscosity drop in the system is due to the nucleation and growth of a
highly sheared band in the gap, whose thickness linearly increases with the
imposed shear rate. We discuss various details of the velocity profiles in all
the regions of the flow curve and emphasize on the complex, non-Newtonian
nature of the flow in the highly sheared band.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
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