Capillary interaction-induced rolling resistance between elliptical particles and its influence on grain column length at pendular state

Abstract This paper investigates capillary torque induced by capillary interaction between mono-sized elliptical disks within the pendular regime. When relative rotation between a pair of elliptical particles (2D disks) takes place, the liquid meniscus between the particles is distorted and generates unbalanced capillary forces around the contact, which further induces capillary torque that is a resistance to particle rotation. The variations of capillary-bridge force and capillary torque with relative particle rotation are determined as functions of relative particle rotation, the degree of saturation and particle shapes. For small rotation between particles, an approximate linear relation can be used to describe the dependency of capillary torque on particle rotation. The maximum capillary torque develops when the rotation angle reaches a critical value. The net capillary attraction between particles, however, monotonically decreases as particles rotate. Comparing with dry conditions, the characteristic length of grain columns of mono-sized elliptical particles within the pendular regime does not change significantly, particularly when the capillary stress is much lower than the net stress.