The relationship between the dynamic effect of a capillary and the length of microchannel in front of a step valve was researched,then the influence of dynamic effect in the process of stopping the capillary in microchannel formed by hydrophobic and hydrophilic walls on the step valve was analyzed. According to the working principle of the passive valve of capillary and energy conservation law, the critical length in front of the step valve was calculated when the step valve stoped the capillary. The calculated length corresponding to the critical length was obtained by numerical simulation. It shows that when the actual length in front of the step valve is greater than or equal to the calculated length, the valve can stop the capillary effectively. The step valves were fabricated by bonding polydimethylsi-loxane (PDMS) to glass. Experiments of stopping the capillary by the step valve were performed in a rectangular microchannel formed by three hydrophobic PDMS walls and one hydrophilic glass wall. For the series of microchannel with a depth of 40 μm and widths from 200 μm to 400 μm, the calculated length in front of the step valve is from 4. 531 6 μm to 10. 081 μm. In the experiments, the actual length before the step valves for effectively stopping the capillary is in the interval from 10 μm to 2 000 μm. The results show that even if the actual length in front of the step valve is 10 μm, the step valve can also stop the capillary. Therefore, the dynamic effect of the capillary can be ignored in stopping the step valves in the microchannel.%分析了由亲/疏水性不同壁面组成的微通道内毛细流动的动态效应对台阶阀截止功能的影响和在台阶阀截止过程中毛细流动动态效应与台阶阀前微通道长度的关系.根据毛细被动阀的工作原理和能量守恒原理,得出台阶阀有效截止时,台阶阀前微通道临界长度的计算公式.通过数值仿真得到临界长度所对应的计算长度,当台阶阀前微通道实际长度大于等于计算长度时,台阶阀即可有效截止.用聚二甲基硅氧烷(PDMS)和玻璃为材料键合制作微流控芯片,在三面疏水、一面亲水的矩形微通道内进行了台阶阀截止实验.对于深度为40μm,宽度为200～400 μm的系列微通道,台阶阀前微通道的计算长度为4.531 6～10.081 μm,在台阶阀前微通道实际长度为10～2000 μm的微流控芯片内进行的台阶阀截止实验表明,即使台阶阀前微通道实际长度为10 μm,台阶阀也能有效截止毛细流动.因此,在微通道内台阶阀截止过程中毛细流动的动态效应可以忽略.
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