| The paper aims to study and apply the phenomena of laminar flow in microfluidic chip. First, the platform of microfluidic chip was established, concerning technologies of fabrication, detachable torque-actuated valve, interconnector and tubing(resistant to pressure and organic phase) connecting chip and other equipments. Second, on the basis of the established microfluidic platform, the laminar flow of miscible flow and immiscible flow and its manipulation were studied. At last, laminar flow was applied in microfabrication of glass structure, solvent extraction and in-channel metal pattern. The specific content is described below:1. Detachable torque-actuated valve. To satisfy the needs of microfluidic chip in the situations of Point-of-care and resource-poor, a detachable torque-actuated valve was developed. This kind of valve can be assembled with microfluidic chip repeatedly. After the chip has to be abandoned, the valve could be detached and continue to use with a new chip. It reduces the cost and enhances the efficiency of valve. Additional, the finite element model of a thin polydimethylsiloxane membrane was established to better understand the operation of the valve.2. Adjustable vacuum driven system. Add needle valve and T-junction to the tubing of vacuum water pump. The needle valve can adjust the vacuum and then the velocity of flow in microfluidic chip. By varying the velocity, the conversion from laminar flow to bubble flow of liquid and air was achieved. Two independent driving systems can produce laminar flow in a cross channel. By varying the ratio of velocity, the flow behavior of laminar flow and the position of stagnation point can be adjusted. The results of finite element analysis (FEA) are consistent with that of experiment.3. Laminar flow assisted wet chemical etching. Taking advantage of laminar flow in three dimension, the lateral bulk material can be protected and kept from the middle etchant flow. Therefore, the aspect ratio of glass can be improved. The aspect ratio of glass structure through laminar flow assisted wet chemical etching is up to 1, which is as twice as the max aspect ratio by conventional wet chemical etching that is 0.5. Corresponding to the etch mask used in conventional wet chemical etching, such as metal and silicon, the laminar flow was termed as "liquid etching mask". This method eliminates the need of expensive equipment or material.4. Laminar flow for extracting effective components in Traditional Chinese Medicine. By selectively modifying channel, the crude aqueous extract of Danshen (Radix Salvia Miltiorrhiza) can flow side-by-side with dichloromethane solvent. The non-polar components, such as tanshinone, can be extracted into organic phase by diffusing. Thus, the polar components, such as salvianolic acid, and non-polar components can be separated. The extract ratio, up to 92%, was determined by off-chip HPLC. In addition, we compared the efficiency of extraction in two-stream and three-stream laminar flow. A theoretical model based on diffusive length was also established.5. Laminar flow of immiscible flow and metal patterning. Utilizing geometric confinement to generate laminar flow of immiscible liquids. Such laminar flow can be employed in patterning silver and chrome inside channel. Owing to eliminating the diffusion, the pattern of metal is more regular and longer. Besides one dimensional and continuous pattern, metal dot array was also patterned on a surface. This dot array was employed for protein patterning. The laminar flow of immiscible liquids can be used in solvent extraction too. The extract of Rhodamine 6G demonstrates the stability of this kind of laminar flow.6. The theoretical model of immiscible laminar flow. The model of hydrodynamic and Laplace pressures differences was adopted. The calculated results show the ratio of these pressure difference could indicate the change of flow behavior.
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