Evaporation-induced evolution of the capillary force between two grains

Boleslaw Mielniczuk (1, 2) , Tomasz Hueckel (3) , Moulay Saïd El Youssoufi (4, 5)

1 IRSN - Institut de Radioprotection et de Sûreté Nucléaire
2 MIST - Laboratoire de micromécanique et intégrité des structures
3 Duke University [Durham]
4 SIGECO - Structures Innovantes, Géomatériaux, ECOconstruction
5 LMGC - Laboratoire de Mécanique et Génie Civil

The evolution of capillary forces during evap-oration and the corresponding changes in the geometrical characteristics of liquid (water) bridges between two glass spheres with constant separation are examined experimen-tally. For comparison, the liquid bridges were also tested for mechanical extension (at constant volume). The obtained results reveal substantial differences between the evolution of capillary force due to evaporation and the evolution due to extension of the liquid bridges. During both evaporation and extension, the change of interparticle capillary forces consists in a force decrease to zero either gradually or via rupture of the bridge. At small separations between the grains (short & wide bridges) during evaporation and at large volumes during extension, there is a slight initial increase of force. During evaporation, the capillary force decreases slowly at the begin-ning of the process and quickly at the end of the process; during extension, the capillary force decreases quickly at the beginning and slowly at the end of the process. Rup-ture during evaporation of the bridges occurs most abruptly for bridges with wider separations (tall and thin), sometimes occurring after only 25 % of the water volume was evapo-rated. The evolution (pinning/depinning) of two geometri-cal characteristics of the bridge, the diameter of the three-phase contact line and the "apparent" contact angle at the solid/liquid/gas interface, seem to control the capillary force evolution. The findings are of relevance to the mechanics of unsaturated granular media in the final phase of drying.

Mots clés: Capillary force; Capillary bridge; Evaporation; Contact angle; Surface tension

Domaines: Génie civil

Boleslaw Mielniczuk, Tomasz Hueckel, Moulay Saïd El Youssoufi. Evaporation-induced evolution of the capillary force between two grains. Granular Matter, 2014, 16, pp.815 - 828. ⟨10.1007/s10035-014-0512-6⟩. ⟨hal-01102603⟩