Surface tension and elasticity of gel studied with laser-induced surface-deformation spectroscopy

Abstract

The laser manipulation technique was effectively used for agarose solutions and the frequency specstrum of the surface response to the periodical laser irradiation yielded shear elasticity G and surface tension sigma in the gel. The laser spot size, from 60 mum to 200 mum in radius, was chosen so that either the Rayleigh waves or the capillary waves, selectively excited, associated with G or sigma , respectively. The result of G showed a dependence on the agarose concentration that is consistent with the theoretical prediction of the percolation model, while sigma has little dependence on the concentration. The surface state of 0.2 wt.% agarose solution was controlled with sodium-dodecyl-sulfate (SDS) additives, and sigma of the gel and the sol was observed at different SDS concentrations: The result showed (i) sigma decreased with increasing SDS concentration up to 39 x 10-3 mol/l and kept a constant value thereafter, and (ii) the gel and the sol have the same value of sigma and the same dependence on the concentration. These results were considered from a viewpoint of surface pressure and a partially quantitative discussion was made on the surface adsorbed with SDS and agarose molecules.

Vibrations of sessile drops of soft hydrogels

“…Where, V is the volume of the gel sphere. Similar equation has been observed by various authors for the case of a half space, in which the surface wave vector takes the place of 1/R [1,[3][4][5][6]. In our problem, as stated above, the wave vector is pinned by the perimeter of the drop.…”

“…In recent years, estimation of the surface tension and the elasticity of soft gels has become the subject of considerable interests [1,2]. Starting with the pioneering study of Harden, Pleiner and Pincus (HPP) [3], several studies have focused on identifying the capillary and the elastic modes of vibration of either a half space or a thin film of the gel in terms of the various wave vectors that its free surface displays [4][5][6][7].…”

Slow flows of yield stress fluids: yielding liquids or flowing solids?

“…This assumption appears to be in agreement with existing measurements (Yoshitake et al 2008, Jalila and Coussot 2013, Aytouna et al 2013, Jorgensen et al 2015. It remains that a direct measure of interfacial tension with YSF is a challenge because, in such materials, there might exist, even at rest, residual stresses which can preclude a straightforward appreciation of interfacial stresses.…”

Straight contact lines on a soft, incompressible solid

“…where sgn(x'-x) designates the sign of x'-x. Note that (34) is not a first order development but a rigorous result, valid for any value of δγ=γ SL −γ S (but of course while remaining in the limit γ<<γ S and γ<<γ SL of the whole paper). It seems difficult, for this first exploration of our method, to solve the obtained integral equation ruling ζ(x), but it is possible to calculate this extra term in the limit δγ=γ SL −γ S << γ S , by using a perturbation method that consists in replacing ζ'(x') with ζ S '(x') in the integral.…”

“…It would be now interesting to measure extensively the wetting hysteresis presented by various soft substrates (polymers, gels, elastomers…) and to try to correlate the results with their surface tension, as well as with their elastic and plastic properties. Surface tensions of the substrate are not always easy to measure, especially the mismatch between wet and dry values, though forcing of waves at the substrate surface by acoustics or optics could offer some means to measure in situ both bulk rheology and surface properties [34].…”