Study Of Microfludic Driving Based On Liquid Crystalline Backflow Effect

Micro-fluidic driving and control technology is an important branch of the micro electronic mechanical system(MEMS), the main component of most sensors and actuators in the micro system, and one of the key technologies in MEMS that needs to develop. Aiming at the disadvantages of the existing micro-fluidic driving and control technology such as the difficulty of miniaturization, small driving force etc., a new micro-fluid driving technology based on the liquid crystalline backflow effect is proposed. With this study, the technology of micro pump and valve can be rapidly developed, and the theoretical achievements of the liquid crystalline dynamics can be enriched. The main contents of this thesis are as follows:(1) Numerical simulation part: we constructed one-dimensional computation model which could connect the upper plate of the cell and the liquid crystalline backflow, deduced the equations of the backflow and reduced them by MAPLE software. On the basis of given boundary conditions, the discretization process was done with the central difference method in space and the two order Runge-Kutta method in time direction. The computation was done by MATLAB software, and the algorithm optimization was also done based on the analyzing of the parallel algorithm, for cycle and the vector calculation methods. Through the numerical simulation, the influence of the factors to the liquid crystalline backflow such as the cell thickness, the voltage and the director was achieved.(2) Experimental preparation part: in order to meet the requirements of the experiment, a high voltage output waveform generator was designed in this part. The arbitrary waveform output was achieved by the D/A chip through a current-voltage conversion circuit, and the whole process was controlled by the SCM(single chip microcomputer). The arbitrary waveform output was achieved by the D/A chip through a current-voltage conversion circuit, and the whole process was controlled by the SCM(single chip microcomputer). The high voltage output for four channels was achieved by the PA08 voltage amplification circuit. The output data source came from A/D data acquisition process by MATLAB. The amplitude adjustment of the waveform was realized by changing the data source on the base of the maximum data Dmax, and through changing the output time between two adjacent data, the frequency could be adjusted. The reference voltage was decided by the variance of the output voltage and the D ratio. The waveform generator can achieve the following functions: arbitrary output adjustment for the waveform, the amplitude, the accounted, the duty ratio and the phase angle with any one of the four channels, the highest output voltage is 110 V. The output frequency range depends on communication mode and the programming method of the D/A chip. When the PCF8591 is selected, the adjustable frequency range is 0.76Hz-1.14 Hz, and when the DAC0832 is selected, the frequency range can be expanded to 0.76Hz-625 Hz.(3) Experimental part: in order to verify the theoretical calculation results accurately, the experimental model same as the calculation model was needed, namely the liquid crystalline cell with free upper plate. But there is only one type liquid crystalline cell with two plates fixed used in the liquid crystal display field on the market, so the first step of the experiment study is to make the cell. One direction driving cell was made by the following four steps: the cutting and cleaning of the ITO glass, the alignment layer coating on the ITO glass, the rubbing alignment of the ITO plate, and the liquid crystal filling to the cell. Second step, by applying different kinds of electric fields to the different kinds of liquid crystalline cell, the observation of the upper plate movement process by the polarizing microscope was completed, and the digital image data were achieved. Last step, we did the image processing by MATLAB software and got the tracing line of upper plate. Through comparative analysis of the theoretical and the experimental data, the following conclusions can be achieved: qualitatively, the simulation data and the experimental data agree very well, and there is a certain gap between them quantitatively.On the basis of one direction driving experiments, we also did the experiments of two and four directions driving, respectively. The special liquid crystalline driving cells were designed and the self-made waveform generator was used to apply the electric field, and we achieved excellent results. By the combination of designing cell process and the electric field applying process, the upper plate of the liquid crystalline cell can be driven to move to the arbitrary direction with the arbitrary velocity.Through the study work, we confirmed the possibility of the liquid crystalline backflow used in the micro-fluidic system as the power source. The actuators or sensors based on the liquid crystalline backflow effect have many advantages comparing to other existing micro-fluidic method: simple design and production process, easy to realizing miniaturization, large driving force, and arbitrary driving directions and velocity. This new driving method based on the liquid crystalline backflow effect can effectively make up for the existing micro-fluidic methods, and has much significance to the development of the micro-fluidic system.