Numerical analysis and experiments of capillarity-driven microfluid chip

Pumping of fluid is an important issue in the microfluidic system. Surface-directed capillary pump merits no external power input and low pressure drop in the microchannel compared to external syringe pump and built-in powered pumps. In this article, the numerical analysis and experiments of the capillarity-driven fluidic flow in the microchannel have been investigated. Varied width-to-depth-ratio microchannels were designed for simulation and experiments. The surface hydrophilicity of PDMS and glass materials was examined for fluidic chip fabrication and flow test. Low-viscosity DI water and high-viscosity human blood were used for capillarity-driven flow measurement. PDMS surface was first performed by oxygen plasma treatment for hydrophilic surface to enhance capillary force. But the hydrophobic recovery of PDMS occurred several ten minutes after oxygen plasma treatment. So, the intrinsic hydrophilic glass chips were used for high-viscosity human blood test. The flow velocity of fluid was relevant to the channel geometry and fluidic viscosity. It increased with width-to-depth ratio at constant channel depth and decreased with viscosity. The experimental results had a good agreement with simulation. It offered a good reference for future capillarity-driven microfluidic device in biomedical or biochemical application.