Structural similarity between dry and wet sphere packings

Abstract

The mechanical properties of granular materials change significantly in the presence of a wetting liquid which creates capillary bridges between the particles. This results e.g.in a reduced value of the volume fraction when a packing is prepared with added liquid. Here we use x-ray tomography to demonstrate that this change in mechanical properties is not accompanied by structural differences between dry and wet sphere packings when compared at the same volume fraction. We characterize the structure of the packings by the average numbers of contacts of each sphere á ñ Z and the shape isotropy b á ñ 0 2,0 of the Voronoi cells of the particles. Additionally, we show that the number of liquid bridges per sphereá ñ B is approximately equal to á ñ + Z 2, independent of the volume fraction of the packing. These findings will be helpful in guiding the development of both particle-based models and continuum mechanical descriptions of wet granular matter.

Challenges in `seeing' through particulate materials

“…A 3D scan of a typical granular sample (e.g. a plastic container of 80 mm diameter filled with 3.5 mm plastic spheres) will require between 30 to 120 minutes with a typical commercial inhouse tomography setup, assuming a resolution of 1000 3 voxels with 80 µm edge length [66]. In this time 1400 projection image are taken while the sample is rotated between the images, by 360 • in total.…”

“…Studying liquid bridges between plastic spheres is difficult due to the small contrast. However, by using bromodecane, or water with a high concentration of CsCl or KJ dissolved in it, we can generate 3D images where all three phases: plastic spheres, liquid bridges, and interstitial air, correspond to well separated gray value ranges [66]. Responsible for this effect are here the high Z components bromine, cesium, or iodine.…”

Challenges of 'imaging' particulate materials in three dimensions

“…Studying liquid bridges between plastic spheres is difficult due to the small contrast. However, by using bromodecane, or water with a high concentration of CsCl or KJ dissolved in it, we can generate 3D images where all three phases (plastic spheres, liquid bridges and interstitial air) correspond to well separated gray value ranges [91]. Responsible for this effect are here the high Z components bromine, cesium, or iodine.…”

Connecting particle clustering and rheology in attractive particle networks

“…6,7 The coordination number was also the parameter of choice used by Dibble et al 8 amongst others to describe particle mobility in depletion gels with varying attraction strength as present in less clustered morphologies. 9 Besides coordination number, several other network parameters have been investigated. In another depletion gel study, the rigidity of an attractive 3D particle network was characterised using the fractal dimension from image analysis.…”