Research

Self-propulsion by spontaneous symmetry breaking

At the UNC Physical Mathematics Lab, we are investigating a novel class of fluid transport methods using external vibrations that result from a spontaneous symmetry breaking of the interface.  We found that bubbles exhibit self-propulsion by shape oscillation when they are periodically forced inside a vibrating liquid against a wall. The novelty of these "galloping bubbles" lies in the fact they are able to move efficiently in directions perpendicular to external forcing, which would be useful for guided propulsion for heat transfer and microfluidic applications.

Forced vibrations may also allow millimetric particles on an interface to break the symmetry of vertical motion and undergo a spontaneous "walk" along the interface. The self-propelling particles provide new directions of interfacial manipulation and wave-mediated granular material.

Diffusion-induced transport in stratified fluid

At the UNC Fluids Lab, we are interested in the spontaneously generated horizontal motion of neutrally buoyant particles suspended within a stratified domain. The diffusion of solute external to a curved boundary naturally creates a boundary layer flow that creates a mutually attractive force between particles leading to large-scale aggregration. Similar phenomena may even be observed in particles in stratification close to a solid wall, which shows a horizontal settling mechanism that may help us understand marine particulate flows.

Wetting on complex surfaces

Spreading and transport of liquid drops on solid surfaces is important in many applications such as coating, condensation, and microfluidics. We study wetting phenomena on soft substrates, where substrate deformation from liquid surface tension introduces unique phenomena that can be harnessed in novel fluid technologies. One such example is the potential to generate passive droplet transport inspired by cellular durotaxis. Soft wetting gives rise to a two-way coupled mechanism between a deformable viscous drop and a deformable solid surface that does not follow classic wetting laws for rigid substrates.

Elastocapillary instabilities

Multiscale interaction between bulk and surface forces of low-elasticity solid materials gives rise to a wide range of pattern formations that are relevant in practical problems like tissue bioprinting. Many intriguing fluid-like instabilities are caused in soft materials by non-trivial capillary actions, among which we have studied the dynamics of drop vibration, Plateau-Rayleigh, and Rayleigh-Taylor instabilities through first principle modeling and comparing with experiments.

Free surface flow

I am also interested in the steady interfacial patterns that may be formed on a free surface fluid flow where the characteristic geometry is governed by capillary effects. We have investigated the curious phenomenon of polygonal hydraulic jumps where, under certain experimental conditions, a circular hydraulic jump can break its symmetry and assume a steady polygonal shape whose corners show a universal shape regardless of the overall geometry.