Experimental study of forces between quasi-two-dimensional emulsion droplets near jamming

Abstract

We experimentally study the jamming of quasi-two-dimensional emulsions. Our experiments consist of oil-in-water emulsion droplets confined between two parallel plates. From the droplet outlines, we can determine the forces between every droplet pair to within 8% over a wide range of area fractions φ . We study three bidisperse samples that jam at area fractions φ c ≈ 0.86. Our data show that for φ > φ c , the contact numbers and pressure have power-law dependence on φ − φ c in agreement with the critical scaling found in numerical simulations. Furthermore, we see a link between the interparticle force law and the exponent for the pressure scaling, supporting prior computational observations. We also observe linear-like force chains (chains of large interdroplet forces) that extend over 10 particle lengths, and examine the origin of their linearity. We find that the relative orientation of large force segments are random and that the tendency for force chains to be linear is not due to correlations in the direction of neighboring large forces, but instead occurs because the directions are biased towards being linear to balance the forces on each droplet.

Dependence of the atomic level Green-Kubo stress correlation function on wavevector and frequency: Molecular dynamics results from a model liquid

“…For example, one would not suppose from our results, as they are the averages over many atoms and times, about the presence of force chains [73][74][75][76][77] or chain-like displacements [78]. It appears that the spherical averaging that we perform also averages out the long range Eshelby field present in the system [39][40][41].…”

Jammed elastic shells – a 3D experimental soft frictionless granular system

“…With 4 th we found a similar power law scaling of hZi, shown in the inset plot with exponent 0.490 AE 0.038, this time in good agreement with numerical simulations 4,8 and 2D experiments on frictional particles, 9 frictionless systems like foams 15 and emulsions. 19,20 However, the double counting of overlap volumes is unsatisfactory, and leads to unphysical volume fractions larger than unity. Note that in 2D frictional disks 9 and 3D emulsions 20 a value of b close to 0.50 was found without applying the double counting of overlap volume.…”

“…Compressed emulsions and foams are the two most widely studied experimental so frictionless systems to date, of which studies on compressed emulsions were performed in 3D. [15][16][17][18][19][20][21][22][23][24] These latter studies have produced a detailed characterization of jammed packings of spherical particles. There are not many other so particles available today to study the nature of jammed matter experimentally.…”

“…This is different from the case of emulsions and foams, jammed packings of which have also been studied. 8,[15][16][17]19 The formation of dimples on the shells resulted in asymmetrical shapes. This asymmetry both in shape of these deformable shells and in intensity distribution precluded a straightforward use of available particle nding and tracking algorithms.…”

Preface: Focus on imaging methods in granular physics

“…Since then, the emulsion measurement technique has grown to include a range of 3D force measurement techniques, including at larger granular length scales for frictionless particles. 66,78,79 In all cases, the central challenge is to measure the size of the contacts, which proceeds using similar techniques to those described in Section II. As described in a Focus Issue article, 34 such measurements are now possible while simultaneously performing mechanical tests under realistic strains.…”