Flow characteristics of hydrophilic/hydrophobic capillaries considering surface tension

The surface tension driven flow characteristics should be considered for the initial priming of microfluidic chips with the hydrophilic or hydrophobic surfaces. The hydrophobic capillaries have been prepared by exposing the hydrophilic glass capillaries to pure hexadecane and an octadecyltrichlorosilane (OTS) solution. The displacements and velocities of fluid menisci in two kinds of tubes are measured while changing the inlet pressures. Numerical solutions of fluidic equation show a comparable agreement with experimental results when considering the surface tension. It is also shown that partially coated hydrophobic region of capillary could be used as a passive valve.