(357ax) Microscale Steering of Colloids via Chemical Gradients

Overview: My Ph.D. research falls at the intersection of soft matter and transport phenomena, specifically focused on the control and manipulation of colloidal transport for enhanced oil recovery, drug delivery and consumer products applications.

During my Ph.D., I developed experimental and theoretical expertise in soft matter (colloids, surfactants, polymers), microfluidics, and fluid dynamics through R&D experience in Oil & Gas and Consumer Products industry. I am a fast, avid learner with an aptitude for hypothesis-driven, data-oriented thinking, and a passion for building stuff from "atoms" and creative problem-solving.

Research Interests: After Ph.D., I am looking to leverage my technical skills to solve exciting and challenging problems related to soft materials formulation, characterization, and transport in Pharmaceutical, Consumer Products, Materials, Chemical and Oil & Gas Companies.

PhD Research: Microscale control of colloidal motion is of vital importance in a variety of industrial and biological systems, ranging from consumer products, drug delivery, water filtration, and oil recovery. In such systems, Diffusiophoresis (DP), which refers to directed colloidal migration under solute gradients, has regained attention for targeted delivery of suspended objects, colloidal separation, etc. Most DP experiments till now have been restricted to ambient conditions and electrolyte gradients. Very little is known about how different physicochemical conditions affect DP, e.g., elevated temperatures, and very few experimental techniques exist that allow reliable quantitative DP measurements.

Here, we developed a novel microfluidic approach (Figure 1) that allows us to impose truly steady state gradients and make direct and repeatable DP measurements under a wide range of physicochemical environments. Using this approach, we studied the temperature dependence of DP. We performed experiments at temperatures ranging from 20 ⁰C to 70 ⁰C under NaCl gradients and found DP velocities and mobilities to monotonically increase with temperature in relatively good quantitative agreement with theoretical predictions [1]. Thus, our results give further confidence to DP theory to predict DP mobilities under elevated temperature conditions.

Additionally, while most work has been focused on studying DP under electrolyte gradients, we explored how gradients of dipolar molecules, known as zwitterions, can drive DP motion. Our simple theory predicts DP velocity under zwitterion gradients to scale linearly with the gradient but shows no dependence on the local concentration like in the electrolyte case. We validated the theory experimentally using our microfluidic approach. We also demonstrated that the DP mobilities scale with the square of the zwitterion dipole moment, as predicted by our theory. Our results elucidate a previously unexplored phenomenon and open the possibility for new ways to employ DP.

Overall, with the combination of careful experiments and theory, our work contributes new insights into DP and opens possibilities for new theories and tests of DP phenomena under a wide range of physical and chemical conditions encountered in real-world applications.

References:

[1] Shah, Parth R., et al. "Temperature dependence of diffusiophoresis via a novel microfluidic approach." Lab on a Chip 22.10 (2022): 1980-1988.