Abstract:In order to analyze the dynamic effect in the process of stopping the capillary by the step valve in microchannel formed by hydrophobic and hydrophilic walls

the relationship between the dynamic effect of the capillary and the length before the step valve was researched. First

when the step valve stops the capillary

the critical length before the step valve is calculated according to the working principle of the passive valve of capillary and energy conservation law. Then we obtained the calculated length corresponding to the critical length by numerical simulation. When the actual length before the step valve is greater than or equal to the calculated length

the valve can stop the capillary effectively. The step valves are fabricated by bonding polydimethylsiloxane (PDMS) to glass. Experiments of stopping the capillary by the step valve were performed in the rectangular microchannel formed by three hydrophobic PDMS walls and one hydrophilic glass wall. For the series of microchannel with the depth of 40μm and width from 200μm to 400μm

the calculated length before the step valve is from 4.5316μm to 10.081μm. In the experiments

the actual length before the step valves for effectively stopping the capillary is in the interval from 10μm to 2000μm. Experimental results show that even if the actual length before the step valve is 10μm

the step valve can also stop the capillary. Therefore

the dynamic effect of the capillary can be ignored in the stopping process of the step valves in the microchannel.