| Summary: | 碩士 === 國立成功大學 === 工程科學系碩博士班 === 94 === In this study, we investigate the electrokinetically-driven flow transport phenomena in microfluidic chips experimentally. Two main issues are studied as follows:
Firstly, we study the control of the electrokinetic multiple sample flows focusing/valveless switching in an MxN microfluidic chip based on electrokinetic forces (note: M is the number of sample stream and N is the number of outlet port). According to the electrokinetic body force term in the equation of motion or Helmholtz-Smoluchowski equation, we know that the flows are driven electrokinetically along the direction of the externally applied electrical potential gradient. Therefore, the direction of electrokinetic flow streams can be easily guided by controlling the externally applied electrical potential distributions in microchannels. Experimental and numerical simulation results both show the sample flows can be pre-focused into narrow streams and then guided directly into the desired outlet ports using this simple control model.
Secondly, the electrokinetic instability phenomenon of multi-interface layers (2M) (note: the interface layer between the sample flow and sheath flow) and its application in micro-mixing are investigated experimentally. In practice, there is a difference in electrical conductivity between sample flow and sheath flow, i.e., the electrical conductivity gradient exists at the interface between sample flow and sheath flow. According to the Poisson equation and the Ohmic current model, the net charge density can be expressed as , and then we can know that the net charge density exist in the bulk liquid when the electrical conductivity gradients exist in microchannels, i.e., there are electrical body forces away from the channel walls (i.e., electrical double layer). At critical electrical field strength, this induced electrical body force will result in an instability flow field. This unstable flow field can be used to enhance the species mixing in microchannels and the mixing length and mixing time can be reduced effectively. Finally, using the simple control model previously, the electrokinetic instability multi-streams can also be directed into desired outlet channel.
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