| This dissertation is focused on the design and manufacture of polymer mcirofludic chips and the contents are as following:In the first part, the general situation of microfluidic chips research is reviewed. The structure of microfluidic chips, the selection of the chip's materials, the manufacture of the microstructure and the measurement on the microfluidic chips are introduced. The hot embossing and bonding are emphasized and their merit and shortage are pointed out. Based on these, the numerical simulation and experiment on the manufacture of microchips are analyzed and the technical scheme and research contents are presented.In the second part, the hot embossing process is investigated. A polymer micro hot embossing process is characterized by experiment, a series of experiments were carried out with varied process conditions, including processing pressure, temperature, time, different materials and unload temperature, and both the depth and width of hot-embossed microchannel was investigated. The conclusions can be obtained as following: Firstly, when the temperature is lower than material glass temperature, the depth of the microchannel is incomplete. When the temperature is close to or exceeds the glass temperature, the depth is hardly variable and equal to the highness of the template's raised size.Secondly, the width of the microchannel shows a ladder under various embossing temperature, namely, when the temperature is lower than glass temperature( low temperature stage), the with of the mcirochannel is nearly constant, its value less than the template aΔ1 and it not affected by the pressure, time and the width of the template's raised region. When the temperature is exceed the glass temperature(transition stage), the width increases with the increasing of the temperature, namely,Δ1 is decreased gradually. When the embossing temperature is more highly than the glass temperature(high temperature stage), the width is constant except its value is also less aΔ2 than the template's raised region, furthermore, theΔ2 is constant andΔ1>Δ2. When the temperature is extra high (extra high temperature stage), the width is instability and often caused distortion or air bubble, the process is difficult to control.Thirdly, the effect of the pressure and time on the sizes of the microchannel is small and is not necessary to adopt high pressure or too longer time. The law of is similar for different width of template's raised region, different material and demolding temperature (lower than the glass temperature).Fourthly, in order to improve production efficiency, it is better to using non-thermal hot embossing when handles thick substrates.In the third part, the hot embossing process is investigated by numerical simulation. A finite element simulation based on a viscoelastic model is carried out. The variation of the depth and semi-width of the microchannel under different processing temperature, pressure, time are presented, the temperature distribution, the material flow manner and the distribution of the stress-strain in substrate are characterized and the causes are analyzed. The conclusions can be obtained as following:Firstly, the substrate material had a wave-like flow, which maybe causes nonuniform distribution of pressure and affect the substrate planeness and even the future bonding process.Secondly, the maximum temperature gradient local at the tow low corner of the microchannel, and the temperature gradient at low surface of microchannel is high than the other surface, this will cause the microchannel go up and shrink the width. Thirdly, the horizontal strain gradient of the substrate is larger than that of the vertical, and so the main shrinkage of the microchannel size will occur in horizontal directionFourthly, the imprinting temperature plays an important role in hot embossing process. When the temperature is lower, the depth is shallow. When the temperature is close to the PMMA glass temperature, the depth of the microchannel do not vary much and approaches to the mold feature height. But the width of the microchannel is increasing gradually. when the temperature ranges from 120℃to the 130℃, a stable stage is gained.Fifthly, the effect of the imprinting pressure on the microchannel size is not much. Considering the effect of the error, it can be drawn a conclusion that it is unnecessary to choose excessive imprinting pressure during the hot embossing process.Sixthly, the hot embossing processing can be accomplished in a relatively short time and it is unnecessary to choose an excessive imprinting time during the hot embossing process.In the fourth part, the hot bonding process is investigated. a polymer micro hot bonding process is characterized by experiment for PMMA and PC, a series of experiments were carried out with varied process conditions, including processing pressure, temperature, time, different materials ,unload temperature, both the size changes , the bonding force and age effect of hot-bonding was investigated. The conclusions can be obtained as following:Firstly, in order to control microchannel's size, the temperature is 70℃～90℃and the pressure is 0.15MPa-1.5MPa. The variable of the pressure has little effect on the microchannel size and 10 minutes is appreciated. The top lip's distortion is increasing with the pressure and time. The relation with the temperature is more complex and can be divide into increasing or decreasing at 80℃.Secondly, the variable of the microchannel's size is come from substrate and top lips. In order to decrease the change of the microchannel, nonisothermal bonding method is presented.Thirdly, hot embossing process has little effect. Unloading at 60℃is better. The age effect is small and PC chips have the similar rule. Fourthly, the bonding force is increasing with the temperature, pressure and time. But it must be care of the change of mcirochannel's size during the increasing operation. In the fifth part, the hot bonding process is investigated by numerical simulation. A finite element simulation is carried out. The variation of the shape of the microchannel under different processing parameters is presented, the temperature distribution, the material flow manner and the distortion of the top lip are characterized and the causes are analyzed. The conclusions can be obtained as following:Firstly, the distribution of the temperature has a strong effect on the hot bonding. Adjusting the top lip temperature and maintain the substrate temperature can gain a mild temperature distribution, and the top lip's temperature is arrived at a scheduled temperature while the temperature of the substrate is still low. This can guarantee the bonding force and gain a small size changes.Secondly, the material flow in the substrate and top lip are analyzed. It can be found that the material flows from down to up in substrate while the material flows from up to down in the top lips. This indicate that two regions are crucial for control the microchannel's sizes.Thirdly, under the couple of the heat and pressure, selecting of a lower temperature substrate and a higher top lip can lead a smaller size changes, furthermore, higher top lip's temperature is better to control the temperature distribution around the microchannel.In the sixth part, measurement on microchannels of PMMA microfluidic chips is carried out. Based on CCD-image, a measuring system for polymethyl methacrylate (PMMA) microchannel's sizes of microfluidic chip is developed. Discussing the setup of measurement system, the microchip specimen preparation, the measuring method for microchannel sizes, including image preprocessing, selection of image binary-conversion threshold, secondary calibration, boundary encoding and calculation of microchannel's geometrical sizes, etc. and the reasons to cause the error are analyzed. Compared with those obtained using universal measuring microscope, the measurement results obtained using this method is conformable and the deviation is 2μm (semi-depth width). Experimental results show that this method is correct, feasible, and suiting for measurement under micro scale and simple to use, as well as can avoid the errors often made by stylus profiler in deeper mcirochannels.In the last part, the dissertation is summarized and the future work is prospected.
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