Bubble Clusters in Associative Polymers

Abstract

Groups of bubbles were collected and released in an associative polymer (HASE 1.5%, Hydrophobically modified Associative Soluble PolymEr). The bubbles (volume ?18 mm3) rising in this highly viscous fluid tend to form clusters. The images show clusters formed by different number of bubbles; the number below each image indicates the number of individual bubbles (N) in each cluster. In agreement with what has been observed in the case of settling particles (Jayaweera et al. J Fluid Mech 20:121, 1964; Hocking, J Fluid Mech 20:129, 1964), the bubbles form regular polyhedrons for N < 7. Surprisingly, the bubble clusters do not experience the velocity jump (Soto et al. Phys Fluids 18:121510, 2006) observed for the case of single bubbles having an equivalent total volume. However, the appearance of the characteristic cusped tail is observed on the bubbles near the trailing edge of the cluster.