Studies On Fabrication Of Polydimethylsiloxane Pneumatic Valves And Its Function As A Mixer

Control of the microfluid is the key to the microfluidic systems. Microvalves are one of the most important microfluidic components, and play a critical role in controlling fluid flows in microfluidic systems. Mixing in microscale relies mainly on molecular diffusion due to the laminar behavior at low Reynolds numbers. However, molecular diffusion is generally a slow process, so accelerating microfluid mixing and improving mixing efficiency are important. Based on the advantages of polydimethylsiloxane (PDMS) material and easy fabrication and integration of pneumatic valves, multi-layer and single-layer pneumatic valves were manufactured using PDMS and glass slide in the present work, and microfluid mixing was realized using the multi-layer pneumatic valves.In chapter1, the classification, development and application of PDMS pneumatic valves were reviewed, including multi-layer normally open valve, single-layer normally open valve, normally closed valve. Micro-mixers based on the working principle of PDMS pneumatic valve and integration of PDMS pneumatic valves were also reviewed. Finally, the consideration of our work design was given.In chapter2, a novel pneumatic ejection mixer made of PDMS and glass slide was developed. We investigated the influence factors on mixing efficiency, such as the thickness of PDMS driving film, the applied pressure and driving frequency. The fast and effective mixing with flow rates ranging from1-700μL/min was achieved under the conditions of the pressure of0.24MPa, the driving frequency of62.5Hz and the PDMS diaphragm of30μm in thickness. Meanwhile the mixing was realized with flow rates ranging from750-3500μL/min without the gas disturbance. Passive mixing function of the active mixer was further developed, and the influence factors, such as the number of mixing unit and two fluid barriers, were investigated. Experimental results showed that the effective mixing was realized with flow rates ranging from550-3500μL/min using five fluid mixing units and two fluid barriers in the microchannel.In chapter3, single-layer normally open valve was manufactured using PDMS and glass slide. The operating conditions and geometric parameters of the chip were systematically optimized. The single-layer PDMS pneumatic valves closed effectively the fluid channel with the fluidic channel of100μm in width, gas control channels ranging from1.0-2.0mm in width, PDMS diaphragm of130μm in thickness, an air pressure of0.18MPa, two PDMS components ratio of20:1.In the last chapter, a summary and perspective were given for PDMS pneumatic valves.