Eur. Phys. J. E 1, 41-53
Ultrasound and light scattering from a suspension of reversible fractal clusters in shear flow
P. Snabre1 - L. Haider2 - M. Boynard2
1 Institut de Science et de
génie des matériaux et procédés,
B.P. 5, 66125 Font-Romeu Cedex, France
2 Groupe de Biophysique (GRPB), UFR Biomédicale, 45 rue des
Sts-Peres, 75270 Paris Cedex 06, France
snabre@imp-odeillo.fr
Received 12 November 1998 and Received in final form 17 May 1999
Abstract
Shear break-up of reversible fractal clusters is investigated by
ultrasound and multiple light scattering in the low shear regime. We consider a
dense suspension of Rayleigh scatterers (particles or clusters) with acoustic
properties close to those of the surrounding liquid so that the attenuation of
the ultrasonic coherent field is weak and multiple scattering is negligible. The
concept of variance in local particle volume fraction is used to derive an
original expression of the ultrasound scattering
cross-section per unit volume
for Rayleigh fractal clusters. On the basis of a scaling law for the shear
break-up of aggregates, then we derive the shear stress dependence of the
ultrasound scattered intensity from a suspension of reversible fractal clusters.
In a second part, we present rheo-acoustical experiments to study the shear
break-up of hardened red cell aggregates in
plane-plane flow geometry and
we examine both the self consistent field approximation and the scaling laws
used in microrheological models. We further compare the ability of acoustical
backscattering and optical reflectometry techniques to estimate the critical
disaggregation shear stress and the particle surface adhesive energy. Finally,
the microrheological model from Snabre and Mills
[5] based on a fractal
approach is shown to describe the non Newtonian behavior of a dense
distribution of hardened red cell aggregates.
PACS
42.25.Fx Diffraction and scattering
-
43.35.+d Ultrasonics, quantum acoustics, and physical effects
of sound
-
43.80.+p Bioacoustics
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
