Soft Matter Laboratory Research

Complex Fluids Inside Microfluidic Devices

Nanoporous Synthesis

BioMimetics

Bioenergy

Energy Storage

Granular Materials

Complex Fluids Inside Microfluidic Devices:

Complex fluids are liquid-like but differ from simple liquids as a result of colloid, polymer, and surfactant interactions. The internal structure of complex fluids spans nanometer to micrometer length scales and exhibits complicated dynamics with multiple characteristic time scales. As complex fluid applications broaden, it becomes increasingly important to improve their large-scale manufacturing efficiency. Microfluidics is an emerging technology concerned with the design and application of fluid networks with extremely tiny fluid networks ranging from a few microns up to as large as a few millimeters. Microfluidics holds great promise as it offers both relatively rapid transport and the ability to manipulate smaller sample volumes than what is conventionally possible. These factors allow small sample volumes to perform tests from dynamic environments and provide immediate feedback which is critical for non-equilibrium kinetic effects on the self-assembly within colloidal suspension droplets as their solvent composition changes.

Project 1: Emulsion droplet formation

The formation and manipulation of droplets, particularly on the micron scale, has many potential applications such as food production, actuators for micro-pumps, chemical reactors, the rapid screening of protein crystallization, and microcultures. Microfluidic devices offer a unique method of creating and controlling droplets on these small scales and have recently been the focus of much research. We have been exploring the length scale, fluid elasticity, and channel surface energy effects on the droplet pinch-off dynamics of both Newtonian fluids and polymer solutions.

Project 2: Droplet deposition and length scale effect

When a droplet approaches a solid surface, a thin liquid film forms between the droplet and the surface, drains until an instability forms and then ruptures. In this study, we utilize microfluidics to investigate the effects of film thickness on the time to film rupture for water droplets in a flowing continuous phase of silicone oil depositing on solid poly(dimethylsiloxane) (PDMS) surfaces. The water droplets ranged in size from millimeters to microns, resulting in estimated values of the film thickness at rupture ranging from 600 nm down to 10 nm. The Stefan-Reynolds equation was used to model the film drainage beneath the millimeter-scale and micron-scale droplets. Comparison between the analytical and experimental film rupture times revealed that the drainage Stefan-Reynolds equation was unable to accurately predict the time to rupture for micron scale droplets without taking into account increases in the effective viscosity of the thin film. These differences in film rupture times between the millimeter and micron scale indicate confinement induced entanglement of the silicone oil molecules as the film thins to thicknesses on the order of tens of nanometers underneath the micron-scale droplets.

Project 3: Liquid crystal droplets

Liquid crystal materials were first discovered in 1888 by an Austrian botanist, F.\ Renitzer. Liquid crystals are long rod-like structures known as mesogens that tend to point along a common axis. The liquid crystal phases can range from a crystalline solid to an isotropic liquid. Because of their unique features, liquid crystals are widely used in display (LCD) technology and photonics materials. Since liquid crystal droplets with adjustable size can provide certain refractive index profile, which can act as switchable prism gratings, as well as positive and negative lenses with tunable focal lengths, we have been using microfluidics to produce monodisperse or polydisperse liquid crystal droplets. This work is in collaboration with Professor James Feng from University of British Columbia.

Some Past Projects:

Project 1: Fiber coating with complex fluids:

Project 2: Roll coating with polymer solutions:

Project 3: Drying of complex fluids: