Paper Number
NF2 

Session
Non-Newtonian Fluid Mechanics & Instabilities

Title
Dynamics of dimples on bubbles approaching free interfaces in wormlike micellar solutions

Presentation Date and Time
February 14, 2017 (Tuesday) 4:00

Track / Room
Track 2 / Audubon A

Authors (Click on name to view author profile)

1. Chandran Suja, Vineeth (Stanford University)
2. Kannan, Aadithya (Stanford University, Department of Chemical Engineering)
3. Kubicka, Andrew (Portola Valley School)
4. Fuller, Gerald G. (Stanford University, Department of Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Vineeth Chandran Suja¹, Aadithya Kannan¹, Andrew Kubicka², and Gerald G. Fuller^1
1Department of Chemical Engineering, Stanford University, Stanford, CA 94305; ²Portola Valley School, Portola Valley, CA 94028

Speaker / Presenter 
Chandran Suja, Vineeth

Text of Abstract
Bubbles approaching free interfaces from the bulk of a liquid, often deform and entrain liquid to have a local maxima in the film thickness at the centre of the bubble called as a dimple. The dynamics of these dimples are known to play an important role in bubble stability, with dimple washouts initiating complex Marangoni instabilities in the presence of surfactants. However no literature exists on the dynamics of dimples in worm-like micellar solutions where the effects of bulk rheology play a significant role. We report experimental data from single bubble drainage experiments focused on the drainage dynamics of the dimples at different Capillary (Ca) and Deborah numbers (De). In wormlike micellar solutions [cetyltrimethylammonium bromide (CTAB) + Sodium Salicylate (NaSyl)], the washout dynamics of dimples is seen to be influenced by the micellar structures. At low surfactant concentrations (spherical micelles), the dimples are seen to become unstable at low Ca and have larger washout velocities (compared to higher surfactant concentrations) for a given Ca. However, at higher concentrations, the entangled polymer structure of the micelles stabilizes the dimples against washout at low Ca. Further at these concentrations, depending on the reptation times (characterized by De), complex washout dynamics involving rapid dimple deceleration, recoil and oscillatory washouts are observed at different Ca.