Nano- and Micro-fluidics
Miniature fluidics and networks are designed, fabricated, and used to understand various transport and interfacial problems and applications at small scales. For example, slippage phenomenon in microfluidics is experimentally investigated for a pressure-driven flow in a variety of micro- and nano-structured hydrophobic microchannels. These channels are chemically hydrophobic and microscopically patterned. The combination of surface roughness and water repellency can promote gas layers upon the hydrophobic walls, thereby providing shear-free boundary conditions and enhancing flow velocity. Other current investigations of the group include electrokinetic flow for electrodialysis and desalination, heat, and momentum transport over slippery, superhydrophobic surfaces, and complex fluids such as emulsions and soft matter in micro-channels. We often utilize experimental techniques such as micro-particle image velocimetry and high-speed, microscopic imaging to obtain high-resolution flow fields and ultrafast dynamics at the pore scale.
In contrast to a simple Newtonian fluid with a constant liquid viscosity, complex fluids--binary mixtures of different phases-- have a nonlinear response of liquid viscosity to the external shear stress. Complex fluids are omnipresent in food, cosmetics, oil, biological and medical industries; some examples are colloids (solid in liquid), foams (liquid-gas mixtures), emulsions (droplet in another immiscible liquid), and biofluids. We measure rheological properties (i.e., viscous and elastic responses) of complex fluids and investigate their motions and stability under extreme conditions (such as under high shear, temperature, pressure).
Wetting & Drop Impact
A droplet sitting or impinging on a surface is a ubiquitous and essential process in Nature and industry. For instance, the static wetting and dynamical interactions between a droplet and solid play an important role in agrochemical, spraying, heating, cooling and (3D) printing technologies. The interplay of several parameters: liquid type, surface property, and surrounding gas, often produces surprising outcomes. We experimentally examine wetting and impact dynamics of a droplet on a variety of surfaces using high-speed imaging. The aim is to understand the effects of small-scale roughness, micro-textures, impact velocity, droplet rheology, and air pressure on the drop impact outcomes in different applications.
Porous Media Flow
Flow motion in porous media plays a crucial role in fuel cells, membrane technology, oil and gas industry, and biological applications. We investigate two-phase flow in both pore structures and large-scale porous media. In particular, we study how interface property, pore structures, and fluid mixtures influence the flow paths in a porous medium. The direct implications from our experimental or numerical results include convective transport in porous media for CO2 sequestration and utilization for enhanced oil recovery.