We study how electrolytic concentration gradients drive fluid and colloidal transport in confined porous geometries, where conventional advection is weak or absent. Our recent work demonstrates that the orientation of salt gradients can fundamentally alter transport in dead-end pores, enabling asymmetric injection and withdrawal of particles with markedly different time scales and spatial structures. Combining theory, microfluidic experiments, and simulations, we investigate diffusiophoretic and diffusio-osmotic transport across pore scales, from single dead-end channels to disordered and macroscale porous media.

One of our interests is in studying how microswimmers or active particles (ex: bacteria in fig. on top-left) navigate flows that are rendered complex due to confinement or inherent non-linearities like inertia and non-Newtonianness i.e., departures from Stokesian assumptions.

We intuitively know that the addition of particles in fluid & flows only makes the fluid thicker. That is why coffee/tea is thicker than water.

Active microscopic particles, however, are capable of reducing the apparent viscosity and making the fluid appear thinner due to active disturbances generated while swimming. Recently, we studied how the activity of such elongated microswimmers can yield fundamental modifications to the orientational dynamics in viscoelastic fluids (top-right schematic). These alterations are found to be activity-specific (whether it is E.coli or Chlamydomonas) and strong enough to sustain the biological noise, and hence substantially impact the bulk suspension viscosity.

Although microchannels offer a high surface area to volume ratio, several reaction processes are limited due to sole reliance on slow diffusion, which causes the formation of undesired products and safety hazards. One of our interests is in intensification methods and modeling of such systems through CFD simulations. For instance, a gently curved channel produces vortices, which generate cross-section mixing and enhancement in heat and mass transport.

Synthetic swimmers such as Janus particles and rods can propel themselves by generating concentration gradients along their surface. This results in a 'diffusio-osmotic' slip which consequently propels the particle autonomously. A significant portion of the potential applications lies in drug-delivery and biological fluid systems which exhibit non-Newtonian behavior, which motivated us to study the changes in the slip and swimming of Janus particles in complex fluids. We also developed a semi-analytical framework to model the hydrodynamic interaction of such swimmers with confinements and externally applied chemical gradients.

Cross-stream migration of particles suspended in fluid flows occurs due to inherent non-linearity: inertia or polymeric stresses. This physics, in the past, has been utilized in microfluidics to focus cells in biological fluids. Recent experimental studies, towards the manipulation of focusing via external fields, have drawn our attention to ask: how electrokinetics affects the particle migration in non-Stokesian flow conditions? The use of classical mathematical techniques (such as perturbation theory and asymptotics in conjunction with reciprocal theorem) has helped us gain fundamental insights into the migration of charged particles and reveal the primary source behind the breaking of symmetry in weakly inertial and viscoelastic flows.