Research

My primary research areas are wettability, droplet dynamics, lubrication flows, interfacial phenomena, rheologically complex fluids, and nonlinear dynamics. I am particularly interested in identifying key fundamental questions in industrial challenges, and translating them into lab-scale bench-top experiments. An up-to-date list of my publications can be found in my Google Scholar page, while a chronological summary of some of my projects are presented below. Please feel free to reach out if you have any questions or comments.

Spreading of gas bubbles on submerged wettability-confined tracks

An experimental investigation of the spreading of a gas bubble on a submerged, wettability-confined track revealed that the gas bubble, while remaining pinned at one end, spreads at a linear rate. Moreover, an inertio-capillary force balance was found to describe the experimentally-observed spreading dynamics with excellent agreement. Please refer to the corresponding publication for more details.

Precision handling of gas microvolumes via wettability-patterned permeable surfaces

The interactions of rising gas bubbles with submerged air-attracting, air-repelling, and wettability-patterned permeable surfaces were studied experimentally, with the goal being to precisely manipulate gas microvolumes by modifying the extent of wettability-patterning of the surface. Superaerophobic meshes were observed to selectively allow the passage of air bubbles depending on its geometry and the momentum of the incoming bubble, while superaerophilic meshes reduce or amplify the volume captured from a train of incoming bubbles. A spatial wettability pattern on the mesh can control the size of the outgoing bubble. This work was supported by the TOP-UIC program between Politecnico di Torino and University of Illinois at Chicago, and the UIC Graduate College via the Dean's Scholar Fellowship. Please refer to the corresponding publication for more details.

Explosive behavior during bicomponent droplet impact on superheated substrates

An experimental investigation of the impact of bicomponent droplets on superheated substrates revealed a new regime, termed as 'explosive boiling', in the traditional temperature-Weber number map. In this regime, the droplet, upon impact, was observed to spontaneously disintegrate into smaller volumes. We proposed that this new regime has its roots in the non-ideal behavior of the liquid mixtures. Furthermore, we present a possible mechanism of the post-impact disintegration of the droplets in this regime. This work was supported by the UIC Graduate College via the Dean's Scholar Fellowship. Please refer to the corresponding publication for more details.

Drop impact on a wettability-patterned permeable substrate

A water droplet impacting a superhydrophobic permeable substrate bounces on top of the substrate, with some liquid penetration being observed on the other side. On the other hand, when it impacts on a permeable superhydrophilic substrate, it penetrates through without any bounce. In this work, we experimentally demonstrate that drop impact on a wettability-patterned substrate can show both bouncing and penetration behavior, with the heterogeneity in the wettability of the substrate resulting in a conversion of the pre-impact vertical momentum of the drop into horizontal momentum post-impact. Furthermore, we present a simplified model based on the energetics, which qualitatively predicts the experimental observations. This work was supported by the UIC Graduate College via the Dean's Scholar Fellowship and Kimberly-Clark Corporation. Please refer to the corresponding publication for more details.

Manipulating circular hydraulic jumps via wettability-patterned substrates

Orthogonal liquid jet impingement on a wettable (hydrophilic) substrate results in a circular hydraulic jump, while the thin liquid film breaks up into droplets post jet-impact on a non-wettable (superhydrophobic) substrate. In this work, we demonstrated experimentally that wettability patterning an initially non-wettable substrate not only arrests the thin film break up by forcing a hydraulic jump, but can also result in the precise control of the location and radial extent of the jump. Furthermore, we developed a theoretical model which demonstrated excellent agreement with the experimental observations. This work was supported by Kimberly-Clark Corporation. Please refer to the corresponding publication for more details.

Directional spreading of droplets on wettability-patterned substrates

Droplets deposited on a wettability-patterned substrate were observed to spontaneously spread, at rates up to 40 cm/s, without any external actuation. The diverging shape of the wettability pattern results in an unbalanced Laplace force in the forward direction, which drives the spreading. From experiments and corresponding scaling analyses, three distinct regimes of spreading were observed: a Washburn-type slow spreading, a much faster (and novel) Laplace pressure-driven spreading, and, finally, a sluggish density-augmented Tanner-type film spreading. This work was supported by Kimberly-Clark Corporation. Please refer to the corresponding publication for more details.

Distributing high-momentum liquid jets on wettability-patterned permeable substrates

A scalable wettability-patterning approach was developed for distributing high-momentum impinging liquid jets on wettability-patterned porous polymeric substrates. A systematic parametric variation resulted in the selection of an optimum design that allowed for the uniform distribution of a liquid jet (flow rates exceeding 1 L/min) on a 7 cm x 7 cm area with minimal or no spilling over the sample edges. The novelty of the method lies in its ability to harness the momentum of the iquid jet, acting alongside an unbalanced Laplace pressure mechanism, to spread the liquid away from the impact point of the jet and to specific dispensing areas on the porous substrate. This work was supported by Kimberly-Clark Corporation. Please refer to the corresponding publication for more details.

Characterization of the nonlinear dynamics of a ducted inverse diffusion flame

Experimental characterization of the dynamics of a laboratory-scale ducted inverse diffusion flame was carried out using tools of nonlinear dynamics. Several interesting dynamic characteristics were observed such as limit cycles, intermittency, and homoclinic orbits. As the position of the flame within the duct was varied, the system was observed to transition from a type-II intermittency regime to a limit cycle and then again to intermittent behavior. Please refer to the corresponding publication for more details.

Active control of ferrofluid droplet generation in a microfluidic T-junction

The formation of ferrofluid droplets in a microfluidic T-junction, in the presence of an external magnetic dipole, was investigated through 3D numerical simulations employing the Volume-of-Fluid (VOF) method. The position of the dipole with respect to the T-junction was varied. It was observed that the dynamics of the fluid inside the T-junction is strongly dependent on both the position and the strength of the dipole. Please refer to the corresponding publication for more details.

Flow past a circular cylinder with fluid injection from its periphery

2D numerical simulations of flow past a circular cylinder with a miscible fluid being injected from two peripheral slots on the cylinder were carried out. It was observed that the orientation of the slots with respect to the cylinder plays a major role in the downstream flow profile. For an injection of comparable strength, a co-counter flow suppresses vortex shedding, while vortex shedding is still present in the cross-flow. A proper orthogonal decomposition (POD) of the flow field was carried out in order to gain insight into the vortex shedding and mixing modes of the various flow configurations. Please refer to the corresponding publication for more details.