Yung-Chieh Tan

Alternating droplet generation and controlled dynamic droplet fusion in microfluidic device for CdS nanoparticle synthesis

A multifunctional and high-efficiency microfluidic device for droplet generation and fusion is presented. Through unique design of the micro-channels, the device is able to alternately generate droplets, generating droplet ratios ranging from 1 ratio 5 to 5 ratio 1, and fuse droplets, enabling precise chemical reactions in several picoliters on a single chip. The controlled fusion is managed by passive control based on the channel geometry and liquid phase flow. The synthesis of CdS nanoparticles utilizing each fused droplet as a microreactor for rapid and efficient mixing of reagents is demonstrated in this paper. Following alternating droplet generation, the channel geometry allows the exclusive fusion of alternate droplets with concomitant rapid mixing and produces supersaturated solution of Cd2+ and S2- ions to form CdS nanoparticles in each fused droplet. The spectroscopic properties of the CdS nanoparticles produced by this method are compared with CdS prepared by bulk mixing.

Optimization of Shear Driven Droplet Generation in a Microfluidic Device

Hydrophilic and lipophilic interfaces of fluids play an important role in the formation of droplets. A large collection of droplets constitutes emulsions of water dispersive phase into oil continuous phase. Since droplet generation forms the basis of the manufacturing of emulsion, great efforts have been made to understand the science, technological and industrial problems associated with the generation of droplets. This paper presents the optimization of a novel method of droplet generation [1] in a microchannel resulting from the laminar co-flow of water and oil in a T type channel. Water in oil droplets are formed with olive oil (interfacial tension 28mN/m, viscosity 84mPa/s, density 918Kg/m3). At the T-junction, the water stream sent through the middle channel is sheared and cut by the oil stream sent through the outer channel. Competition between interfacial tension and the Laplace pressure at the oil/water interface results in droplets of finite diameter. Fluid properties such as density, viscosity and surface tension and the flow parameters such as pressure, mass flow rate and velocity are varied at the inlets and outlets to optimize size, frequency and periodicity of droplets using CFD-ACE+, a multiphysics modeling tool (CFDRC, Huntsville, AL).Copyright

Controlled fission of droplet emulsion in bifurcating microfluidic channels

An integrated micro fluidic system for controlled fission of water-in-oil droplet emulsions has been designed, fabricated, and analyzed. The system consists of a droplet generator connected to a divergent channel. The fission of water droplets is achieved through bifurcating the flow of the continuous phase surrounding the droplet to generate pressure gradients that deform the droplet until it breaks. The sizes of the splitted droplets are controlled through varying the channel widths and the angle of the bifurcating junction. The fission phenomenon matches with simulation results at defined conditions.

Micro and nano fluidic chips for biosensors

Micro and nanofluidics provide very controlled delivery of reagents and samples for highly sensitive biosensors. Two fluidic platforms are introduced in this paper, the microfluidic droplet emulsion and the electrical field-based microfluidics. Traditional issues in microfluidics such as mixing in low Reynolds numbers can be mitigated using some of our active microfluidic techniques