A new method of water pretreatment for thermal bonding polymethylmethacrylate microfluidic chip was proposed in this paper. The bonding rate (effective bonding area) of microfluidic chip under different pretreatment time was studied and the mechanism of this method was discussed. The main thermal bonding parameters were as follows: bonding pressure 1.4 * 1.9 Mpa, temperature 91 * 93°C, time 360 s. The experimental result shows that this method can increase the effective bonding area, improve the bonding quality of the microfluidic chip compared to the conventional thermal bonding method. The optimal water pretreatment time is 1 h with the bonding rate increased by 34% compared with the conventional thermal bonding method. The pollution to the micro-channels is avoided and the performance of the microfluidic system will be reserved with this water pretreatment method. This method is available for the biochemical analysis of the chip, and holds the benefits of easy-operation, high-efficiency and low-cost properties.
Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9 % and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50-60 lm and substrates flatness error is smaller than 80-90 lm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70-80 lm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.
The uniformity of the porous array seriously affects the performance of the injection-molded parts. In this study, a uniform hole array chip constituted by 384 holes whose radiuses are 1.30 mm is fabricated by precision injection molding technology. To capture the relevance between the uniform dimension of the porous array and the injection molding process parameters, single factor experiment was adopted. Besides, the condensed state of the hole array was studied to give a further explanation of the inner relationship between the hole array and the most sensitive injection process. As for the measurement, the diameter of the hole which next to the gate and away from the gate was investigated by means of universal tool-measuring microscope, and the standard deviation of the hole diameter was chosen to estimate the uniformity of the hole array. Furthermore, the crystal state and interface state were characterized by polarized light microscopy (PLM), used to explain why the difference of those holes appeared. The results reveal that the impact of process parameters on the uniformity of the hole array was ranked as follows: melt temperature, cooling time, mold temperature, injection pressure, injection speed and packing pressure. Besides, the analysis of the condensed state on different melt temperature indicates that the larger grain size is less favorable to the uniform molding, as the melt temperature increases, the difference of cortical thickness between the dynamic template and fixed template sides decreases, product uniformity is improved.
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