Effect of Surface Free Energy on the Surface-Driven Capillary Flow in SU-8 based Glass Microfluidic Devices

Surface-driven capillary flow of dyed water is recorded in the SU8 based glass microfluidic devices fabricated by the standard cleanroom processes. The effect of surface wettability on the surface-driven capillary flow is studied in the individual SU8 based microfluidic devices of glass bottom wall and polyimide bottom wall. The surface-driven capillary flow is faster on the glass bottom wall surface due to the higher polar component of solid surface free energy. Also, the capillary meniscus moves faster on the glass bottom wall surface due to larger capillary pressure in dyed water. The experimental results of meniscus movements are compared with the analytical solutions to determine the diffusion coefficient in each surface-driven capillary flow. The surface-driven capillary flow can be controlled by the variation of surface wettability of inner walls in the microfluidic lab-on-a-chip systems.