- Siddarth Srinivasan
- Doctoral Candidate, Chemical Engineering
- Project: Fabrication of Non-Wetting Surfaces for Drag Reduction and Dynamic Wetting
- co-advised by Gareth McKinley, Dept. of Mechanical Engineering
- B.Tech. Chemical Engineering, IIT Madras, 2009
- Email: firstname.lastname@example.org
- Website: http://www.mit.edu/~ssid/
- Phone: (617) 253-6478
- Office: 66-357
My primary work is on understanding the break-up of non-newtonian fluid jets to control the formation of various structured polymeric surfaces to fabricate liquid-repellent surfaces. The surface morphology generated during our simple air assisted spraying process can be tuned systematically from 'corpuscular' spherical microstructures to a beads-on-string morphology and finally to bundled fibers. I have applied knowledge of polymer theory and fluid dynamics to relate the semi-dilute overlap concentration (c*) and molecular weight (Mw) for our system in which the transition in microstructure is associated with a corresponding transition from the ultra-dilute to the semi-dilute regime; the latter associated with a power-law increase in shear and extensional viscosity that stabilizes the cylindrical jet leading to fiber formation (Srinivasan et al., Polymer, 2011).
My thesis research also involves understanding and characterizing how the wetted-solid fraction of the liquid-repellent surface can be designed to reduce fluid drag in both viscous laminar flows and moderately turbulent flows, leading to a number of practical applications. In laminar flows, we estimate the effective Navier-slip length (bslip) for flow over the 'corpuscular' spray-fabricated liquid-repellent surface which supports a composite solid/air/liquid interface or Cassie-Baxter state (Srinivasan et al, Soft Matter, 2013). The reduction in viscous skin friction due to the plastron is evaluated using torque measurements in a parallel plate rheometer resulting in a measured slip length of bslip=39 microns, comparable to the mean periodicity of the microstructure evaluated from confocal fluorescence microscopy. The introduction of a large primary length-scale using dual-textured spray-coated meshes increases the magnitude of the effective slip length to values in the range 94 microns < bslip < 213 microns depending on the geometric features of the mesh. The wetted solid fractions on each mesh are calculated from free surface simulations on model sinusoidal mesh geometries. The trend in measured values of bslip with the mesh periodicity L and the computed wetted solid-fraction are found to be consistent with existing analytic predictions. We are currently investigating the behavior of this system in moderately turbulent Taylor-Couette flows, where we have obtained drag reductions in excess of 30% at Reynolds numbers of Re ~ 30000.
I have also worked on a mathematical analysis of the gravity driven deformation of drops on non-wetting surfaces (Srinivasan et al., Langmuir, 2011), correlating the wetting dynamics on the barbs and barbules of aquatic birds with diving and wing-spreading behavior (under review) and on developing a hierarchical model to design oleophobic woven fabrics.This work is in collaboration with Prof. Gareth McKinley in the Mechanical Engineering Department.
- Srinivasan, S., Choi, W., Park, K.-C., Chhatre, S.S., Cohen, R.E., and McKinley, G.H. "Drag Reduction for Viscous Laminar Flow on Spray-Coated Non-Wetting Surfaces" Soft Matter 9, 5691-5702 (2013)
- Srinivasan, S., McKinley, G.H., and Cohen, R.E., "Assessing the Accuracy of Contact Angle Measurements for Sessile Drops on Liquid-Repellent Surfaces". Langmuir, 27 (22), pp 13582-13589 (2011)
- Srinivasan, S., Chhatre, S.S., Mabry, J.M., Cohen, R.E., and McKinley, G.H., "Solution spraying of poly(methyl methacrylate) blends to fabricate microtextured, superoleophobic surfaces". Polymer 52, 3209-3218 (2011).
- Kleingartner, J.A., Srinivasan, S., Mabry, J., R. E. Cohen, G. H. McKinley. Utilizing dynamic tensiometry to quantify contact angle hysteresis and wetting state transitions on nonwetting surfaces, Langmuir (2013)
- K-C. Park, S. S. Chhatre, Srinivasan, S., R. E. Cohen, G. H. McKinley.Optimal Design of Permeable Fiber Network Structures for Fog HarvestingLangmuir (2013)