Laser-speckle-visibility acoustic spectroscopy in soft turbid media

Abstract

We image the evolution in space and time of an acoustic wave propagating along the surface of turbid soft matter by shining coherent light on the sample. The wave locally modulates the speckle interference pattern of the backscattered light, which is recorded using a camera. We show both experimentally and theoretically how the temporal and spatial correlations in this pattern can be analyzed to obtain the acoustic wavelength and attenuation length. The technique is validated using shear waves propagating in aqueous foam. It may be applied to other kinds of acoustic waves in different forms of turbid soft matter such as biological tissues, pastes, or concentrated emulsions.

Investigating the origin of acoustic attenuation in liquid foams

“…Both viscosities were found to mostly depend on the median radius R. Interestingly, values of η * wall are close to prediction of Eq. (10), suggesting that the phenomenological law found by Costa et al [16] with rheology measurements is still valid in the kHz frequency range, as already observed by Wintzenrieth et al for shaving foams [20]. As for η bub , its values are two to three orders of magnitude higher than for pure water, and it increases with R. We shall explore its dependence on R, Φ and gas nature in further details in the next section.…”

“…A cos(k th x) + B sin(k th x)] ,(20) for −2R < x < 0 andT 1 (x) = p ρ C p [1 + A cos(k th x) + B sin(k th x)] (21) for 0 < x < e, where k th = (iω/D th ) 1/2 . Constants A,B, A , and B are determined by imposing the continuity of temperature and heat flux both in x = 0 and between x = −2R and x = +e (periodic conditions).…”

Rheology of foams and highly concentrated emulsions

“…(2)) ignores viscoelastic relaxation processes which typically set in above frequencies of the order of 1 Hz and which are due to couplings with interfacial relaxations [26][27][28][29][30]. Moreover, in foams that coarsen, there is a slow mechanical relaxation process due to a temporary local loss of elasticity upon coarsening-induced rearrangements.…”

Bulk rheometry at high frequencies: a review of experimental approaches

“…Different microrheological techniques, e.g. using differential dynamic microscopy (Cerbino and Trappe 2008;Edera et al 2017), diffusive wave spectroscopy (Pine et al 1988;Scheffold et al 2004), passive particle tracking (Mason et al 1997), or active microrheology (Keller et al 2001;Wintzenrieth et al 2014), have been developed and successfully applied. However, they are indirect and therefore require the extrapolation of bulk properties, which can be an issue for instance for heterogeneous systems.…”