Liquid Flow in Rectangular Microchannels with Gradient Wettability Inner Surface Driven by Capillary Force and Gravity

A mathematical model for predicting liquid flow velocity in a rectangular microchannel driven by capillary force and gravity is derived. The model takes into account the additional driving force arising from the wettability gradient on inner surface of a microchannel. The results of model prediction show that the velocity of liquid flow decreases with the length of microchannel and the wettability gradient on channel surface will accelerate the motion of the liquid when the flow-front approaches to the end of the microchannel. The analysis of driving force along the moving path matches well with the flow velocity predicted by the model.