Vineeth Chandran Suja

Doctoral Candidate

Trivandrum, India

M.S. Chemical Engineering, École Polytechnique, France


Research Focus:

A. Bubble Dynamics
Bubbles and aggregates of bubbles in the form of foams are ubiquitous in nature. As part of my PhD, I am exploring the dynamics of bubbles in the following contexts:

(i) Bubble and foam stability in lubricant base oils
Entrainment of bubbles and the consequent formation of stable foam in lubricants is detrimental for the lubricated machinery. Hence, to help mitigate foaming in lubricants, using a previously reported single bubble technique we are investigating the physical mechanisms stabilizing foams in lubricants.              DFI_ExperimentalSetupFig: The experimental setup. a,b. The various parts of the setup. c. An example of the spatio-temporal measurement of the bubble wall thickness in a Group I lubricant.
Current Results: Our experiments indicate that solutocapillary Marangoni flows resulting from the differential evaporation of the various components of a lubricant, promote lubricant foaming. This novel finding underscores the importance of minimizing lubricant base oil mixing during lubricant formulation.
Future work: A common way for destroying foams is by using special additives called as anti-foams. Using a combination of experiments and theory we are currently investigating the mechanism of antifoam action in non-aqueous foams.

(ii) Expansion and contraction dynamics of bubbles on capillaries
The expansion and contraction of bubbles in capillaries are common in many industrial settings and experimental setups, for instance as shown above in the DFI. Using a combination of experiments and theory we investigated the shapes of expanding and contracting bubbles.
Current results:  A quasi-static analysis of the bubbles expanding and contracting capillaries revealed that the bubble shapes exhibit hysteresis. We have termed this novel hysteretic phenomenon as the “bubble shape hysteresis” – the details of which can be found in the paper below.
Future work: The bubble shape hysteresis is a consequence of a cusp bifurcation in the equilibrium shapes of bubbles.  Interestingly, by tuning the parameters of the system and operating the bubble close to onset of the bifurcation, we can vastly amplify the expansion/contraction rate of the bubble relative to the forcing. We are interested in understanding this phenomenon in more detail and finding applications for the same.
icon_paper-graduated-512Chandran Suja, V., Frostad, J. M., & Fuller, G. G. (2016). Impact of Compressibility on the Control of Bubble-Pressure Tensiometers. Langmuir, 32(46), 12031-12038.

(iii) Coalescence of bubbles in worm like micelles
A majority of liquids in which bubbles are commonly found are viscoelastic in nature. We are currently investigating experimentally and theoretically the coalescence of bubbles in model viscoelastic worm like micellar liquids.

Current results: As shown in the video above, our preliminary experiments revealed that bubble coalescence in worm like micellar solutions are intrinsically different from that in traditional surfactant solutions. Notably, in certain worm like micelles, we observed the elastic recoils of dimples that are formed on the bubbles.
Future work: A comprehensive understanding of bubble coalescence in worm like micellar fluids.