Research On Liquid Crystals Microflow Measurement Based On Micro-PIV

Liquid crystal(LC) is a kind of special state between the solid and the liquid, and has both the fluidity of liquid and crystal anisotropy of the solid. These two features make the LC more active under the electrical, magnetic, and temperature field and micro flow which can be controlled precisely can be induced. This makes it possible that the LC can be used as the media for micro-fluidic driving and control field. In order to explore the characteristics and formation mechanism, and the overall features of the liquid crystalline micro-flows, a Micro-PIV system special for measuring the liquid crystalline micro flow was set up in this study. Besides, we did the experiments to measure the LC micro flow induced by the electric field and the temperature field with this system, and got more satisfactory results.(1) In order to verify the results of this system, in this paper we calculated the micro flow under the applied electric field. We combined the continuity equation and the equations referring to the small molecule nematic liquid crystalline Leslie- Erickson theory, constructed the LC flow equations, and deduced the speed of each vector equation. Then, the computation and analysis process were done with the MATLAB software. The main concern point was the velocity profile along the direction of the thickness of the liquid crystal cell.(2) In this study a Micro- PIV system applying to the observation of liquid crystalline micro flow was assembled, mainly including two parts: the flow field excitation and the flow observation part. Among them, the flow field excitation part included the microscope stage, waveform generator and self-made liquid crystal cell. Flow observation and record part included the fluorescence microscope, CCD camera and a computer. Comparing with ordinary Micro-PIV system, tracer particles used in this system must be small solid particle.(3)In this paper we studied the micro flow induced by the electric field with the Micro-PIV system. Key observation point was the micro-flow velocity profile in the liquid crystalline cell. In this experiment, the production of the liquid crystalline cell is critical, including cutting, cleaning, coating and aligning operations to the ITO glass. Then, with two pieces of the operation completed glass, one liquid crystalline cell can be made. After the injection operation, a liquid crystalline cell was completed. The injection material was the liquid crystal 5CB with a certain concentration tracer particles. If the electric field is applied, the micro flow could be observed.(4) This study did experiments about micro flow on the temperature field using the system. The experiment was to observe the changes in crystal defects that occur with temperature changes. The production of liquid crystal cell included cutting, cleaning, and assembly about the ITO glass. Besides, the cell needed to add the mixture of liquid crystal and fluorescent microspheres. Then, the liquid crystal cell was observed under the fluorescence microscope. Besides, it was observed under polarized light microscope.(5) In this paper we also did the comparative analysis with the experimental results and the theoretical results. For the micro-flow experiment of the electric field, the results of the experiment and numerical simulation was consistent well qualitatively. However, there were still some gaps with the values. The main reason for the experimental error was the controlling step of the cell’s thickness, and it needs to be improved. For the micro-flow experiment of the temperature field, because the precision of the microscope hot stage used in the experiment was not enough, and had no cooling function, it was difficult to control the accuracy of the micro-flow in the experiments, so measurements of flow fields was difficult.(6) For the above analysis, in the last chapter of this paper, solutions were proposed to improve laboratory equipment. For the problem of the cell’s thickness, we decided to purchase a professional instrument to control the thickness of the liquid crystal cell for the next experiment. For the microscope hot stage, we designed a special microscope heating-cooling stage which could precisely control the temperature changes in the experimental process. The temperature was measured by the temperature sensor, then, the microcontroller was used to control the whole temperature changing process of the heating-cooling stage. At present, the developing process goes well.