(4bq) Soft and Biological Material Odes: Optics, Dynamics, Elasticity-Extensibility, and Self-Assembly

Motivation and Interests Polymers, colloids, surfactants, liquid crystals and gels are all termed as complex fluids or soft materials, for they respond to stress like semi-solids or squishy materials. A combination of spring-like elasticity and ability to flow makes their behavior viscoelastic. Their ability to flow is itself distinguished by behavior unlike that of common liquids or gases: the complexity comes from their time-dependent, or stress-dependent behavior. Many industrial and biological materials exist or are processed in the form of multicomponent, complex fluids. The ultimate function and use of these materials is dependent on both the physical properties of the constituents as well as on the microstructure formed by them. The relation of the optics, structure and dynamics of complex fluids to order and entropy, thermodynamics and kinetics of phase transitions, elasticity and extensibility and self-assembly is of both scientific and technological interest. My goal is to establish a research program to develop multicomponent, multifunctional materials for use in applications ranging from inkjet printing and spraying of complex, functional materials to the understanding of multicomponent biological fluids . In my graduate studies and post-doctoral research [1-12], I have focused primarily on the optics, dynamics, self-assembly and/or pattern formation in dilute two-component (solute & solvent phase) colloidal dispersions, associative polymer solutions, globular proteins and evaporating polymer or colloidal solutions as described below:

1. Doctoral research [1-7]: "Colloidal gold nanorods, iridescent beetles and breath figure- templated assembly of ordered arrays of pores in polymer films". (Advised by Mohan Srinivasaro, Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA).

(a) Structural origin of circularly polarized iridescence in jeweled beetles [1] (with M. Crne, J. O. Park and M.Srinivasarao) * We determined that the patterns on iridescent beetle Chrysina Gloriosa are structurally and optically analogous to cholesteric focal conics on a free surface.

(b) Colloidal Gold Nanorods [2-3] (with K. Park and M. Srinivasarao) * Using hydrodynamic arguments, determined the conditions required to separate gold nanorods from nanospheres by centrifugation; essential for getting purer gold nanorod dispersions. ** Analyzed patterns formed by self-assembly of gold nanorods to show how ordered patterns formed on TEM grids need not be liquid crystalline. Compiled an extensive review that critically examines optics (absorption and scattering), plasmonics, hydrodynamics and self-assembly of colloidal gold nanorods, along with retracing the historical development of the colloidal science.

(c) Breath-figure-templated assembly of ordered arrays of pores in polymer films [4-7] * Developed a theoretical framework to describe the mechanistic aspects of breath-figure-templated assembly, relating pore size to experimentally-tunable parameters. ** Using transport phenomenon (heat and mass transport), themodynamics and kinetics (nucleation and growth and self-assembly), capillarity, fluid mechanics underlying non-coalescence, and elucidated physics underlying the formation of ordered arrays of non-coalescent water drops.

2. Other research as graduate student

(a) Biomimicry of the structural color of Papilio palinurus butterfly [8] : (with M. Crne, J. Blair , J. O. Park , C. J. Summers and M. Srinivasarao, Materials Science & Engineering) provide an exemplary study where we use coat these films with inorganic oxides and : ?Simulated the reflactance of multilayer stack of Al2O3 and TiO2 films on a breath-figure-templated textured surface to determine the layer thicknesses needed to replicate optical effects of the butterfly Papilio Palinarus.

(b) Opto-microfluidics: Chaotic mixing in microdroplets [9] (Advisors Michael F. Schatz & Roman O. Grigoriev, School of Physics, Georgia Institute of Technology, Atlanta, GA). *Developed a unique technique for fast micro-fluidic mixing & control of flow using thermo-optic actuation. **Imaged 2D sections of flow inside the drops to demonstrate the importance of symmetry breaking and drop viscosity for chaotic mixing.

3. Post-doctoral research [10-13] Advised by Gareth McKinley, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA

(a) Extensional rheology of complex fluids and particle-filled fluids for improved spraying performance [10-12] (with Arezoo Ardekani, James Serdy and Gareth McKinley, Massachusetts Institute of Technology). I am developing experimental protocols for testing shear and extensional properties of associative polymer solutions and particle-filled systems over a wide range of shear and extensional rates, using microfluidic devices and by studying capillary break-up of liquid bridges and viscoelastic jets. Surface tension driven break-up of cylindrical fluid elements into droplets plays a crucial role in the use or processing of many multicomponent, microstructured complex fluids like paints, inks, insecticides and pesticides, cosmetics, food, etc. These industrial fluids are typically formulated using dilute polymer solutions, and are exposed to a wide range of shear (1 - 10⁶ s^-1) and extension rates (in excess of 10³ s^-1). Since the polymer solutions and the resulting dispersions have low viscosity (~10 mPas) and short relaxation times (<1 ms), their non-Newtonian behavior is not apparent in the conventional rheometric measurements. However, the presence of even a dilute amount of polymer alters the character of instability growth and capillary break-up during jetting. The interplay of capillary, inertial, elastic and viscous effects on small length and time scales typically leads to complex dynamics in a necking fluid thread and in some cases, the extensional stresses generated in the neck lead to formation of very thin and stable filaments between drops, or to ?beads-on-a-string' structures. I experimentally study the influence of both elasticity and extensibility on the growth of instability and capillary break-up of harmonically perturbed jets of the viscoelastic fluids. By combining experiments with simulations, we show how and when capillary thinning analysis can be applied to capillary break-up during jetting to measure rheological response of fluids. We also show that how the dynamics of the capillary break-up and satellite formation during jetting is influenced by the amplitude and frequency of the imposed disturbances. (b) Rheology of globular proteins [13] (with A. Jaishankar, MIT & YC Wang, Rheosense Inc) Apparent yield stress, high shear rate viscosity and interfacial viscosity and viscoelasticity of globular proteins.

Synopsis & Future Goals In my poster, I will present snippets from my graduate research as well as from my current post-doctoral work, and a summary of my proposed research. My goal is to establish a research program to develop multicomponent, multifunctional materials incorporating colloids, polymers and liquid crystals for use in applications ranging from fluids for inkjet printing and spraying applications to understanding of multicomponent biological fluids. We will focus first on how rheology and capillarity affect the solution-based processing of functional materials and thereafter study how the drying-induced phase behavior and transport processes affect the microstructure/pattern formation. One of the application-orientated goals of my research would be to develop materials that combine structural integrity and robustness with the required optical functionality (reflection, transmission, absorption) for harvesting solar energy. While the understanding of dynamics and principles of self-assembly is crucial for developing practically useful processing methods, the knowledge of interaction of light with matter is essential not only for observing changes in microstructure during flow abut also for the design of optical or photonic devices. The poster will also present an outline of my future goals in fundamental studies of Soft Matter ODES in biology, .

References

1. V. Sharma, M. Crne, J. O. Park and M. Srinivasarao ?Structural Origin of Circularly Polarized Iridescence in Jeweled Beetles,? Science, 325, 449 (2009).

2. V. Sharma, K. Park and M. Srinivasarao ?Shape Separation of gold nanorods using centrifugation,? Proceedings of National Academy of Sciences, 106(13), 4981 (2009).

3. V. Sharma, K. Park and M. Srinivasarao ?Colloidal dispersion of gold nanorods: Historical background, optical properties, synthesis, separation and self-assembly,? Material Science and Engineering Reports, 65, 1 (2009). 4. V. Sharma, L. Song, R. L. Jones, P. R. Williams and M. Srinivasarao ??Effect of solvent choice on breath-figure-templated assembly of ?holey' polymer films?, EPL, 91, 38001 (2010) .

5. L. Song, V. Sharma, J. O. Park and M. Srinivasarao, ?Characterization of ordered arrays of micropores in a polymer film,? accepted in Soft Matter.

6. V. Sharma and M. Srinivasarao ?Growth of ordered arrays of non-coalescing and monodisperse water drops over evaporating polymer solutions,? (under review in PRL).

7. V. Sharma and M. Srinivasarao ?Non-coalescent water drops,? (in preparation).

8. M. Crne, V. Sharma, J. Blair, J. O. Park, C. J. Summers and M. Srinivasarao ?Mimicry of Papilio Palinurus Butterfly Optical Effects? (under review in EPL).

9. R.O. Grigoriev, M.F. Schatz and V. Sharma ?Chaotic mixing in microdroplets,? Lab on a chip, 6, 1369 (2006).

10. A. M. Ardekani, V. Sharma and G. H. McKinley, ?Dynamics of bead formation, filament thinning and breakup in weakly viscoelastic jets?, accepted in JFM.

11. V. Sharma, A. M. Ardekani, J. G. Serdy, P. Threfall-Holmes and G. H. McKinley, ?The life and death of a viscoelastic jet: Fluid mechanics and rheometry,? (in preparation).

12. V. Sharma, A. M. Aredkani and G. H. McKinley, ?'Beads on a string' structures and extensional rheometry using jet break-up?, 5th Pacific Rim Conference on Rheology, Japan, August 2010.

13. V. Sharma, A. Jaishankar, Y. Wang and G. H. McKinley, ?Apparent yield stress, interfacial viscosity and high shear rate viscosity of Bovine Serum Albumin Solutions,? under review in Biophysical Journal).