Transport Properties Of Electroosmotic Flow In Microfluidic Chips

Microfluidic Chip (MFC) is a novel kind of micro total analytical system. It can enhance the performance of chemical analysis with respect to smaller amounts of samples, higher analysis speed, better sensitivity and low cost, which can be used to in the fields of the analytical chemistry, biomedicine, etc. In this thesis, on the basis of deep analyzing and studying domestic and foreign development conditions and existing problems of MFC, aiming at the problems in the process of the manufacturing and application, the transporting rules of fluid in MFC were studied systematically, using the methods of theoretical analysis, numerical simulation and experimental instruments. The main innovative jobs are as followed:The electrokinetic phenomena, as well as the driving and controlling mechanism of the microfluid are studied firstly. The total project of electrokinetic microfluid was summarized based on its multiphysics field coupling characters, and the general mathematical models of MFC were also analyzed. Based on the finite element method (FEM), the Poisson-Boltzmann equation of electric double layer electric field, the Laplace equation of external electric field and the Navier-Stokes equation of electroosmotic flow (EOF) field were discretized, which form the detailed research scheme of the theoretical analysis and numerical simulation.On the basis of the EOF characteristics in smooth microchannel, the EOF was modeled in rough microchannel with rectangle, triangle, sinusoidal and quasi-fractal roughness element, using the COMSOL Multiphysics based on the FEM, which were all divided into the near-wall and bulk flow area. The simulation results indicate that there is a local max value of EOF velocity in the near-wall area of the rough microchannel and the bulk flow EOF velocity almost keep invariable while the roughness is in the scope of the micrometers. In the whole channel, the average EOF velocity decreased nonlinearly with the increasing of the roughness, which decrease quickly when the roughness element height is 0.3 times of the EDL thickness. The results show the mechanisms of the rough element to EOF, which can guide the friction research of the microflow.The transient and the steady state of the EOF were modeled in hydrophobic and hydrophilic microchannel. The results show that the transient characteristics of EOF are similar in hydrophobic and hydrophilic microchannels, the steady time of EOF is proportional to the square of microchannel scale, and the magnitude is microsecond. EOF velocity in hydrophobic microchannel is proportional to the electric strength and independent of the channel height, and decreases slowly with the ionic concentration, which is lower than that in hydrophilic microchannel. The results can provide the reference for the EOF control in hydrophobic microchannel.The microflow processes, such as sample transport and separation in smooth and rough 3D MFC, were modeled in the level of system. The results indicate that the surface roughness can enlarge the sample zone and there is a "delay phenomenon" in the profile of the microflow, which can be eliminated by adjusting the applied electric strength in microchannels. The results can improve the separate efficiency and accuracy of sample in rough microfluidic chips.Two kinds of polymethyl methacrylate (PMMA) microfluidic chips were planed and manufactured. The surface parameters were also tested. Based on the current monitoring method, the multi-channel EOF experimental systems was designed and build up and the virtual instrument LabVIEW software was also used to develop the data acquisition human machine interface. The EOF in PMMA microfluidic chips was achieved on the experiment system at last.The results of the theoretical analysis, numerical simulation and experiment coincide very well, which have important theoretical significance and practical values to the fundamental research, development and application of MFC.