In our previous work, a new flow route was developed-a so-called perpendicular shear force-induced droplet formation-in a self-designed simple T-junction microchannel device. In this work, the crossflowing rupture technique was used to prepare monodisperse droplets in a similar device and successfully prepared monodisperse droplets ranging from 50 to 500 mu m with polydispersity index (sigma) values of < 2%. Two kinds of flow patterns of plug flow and drop flow in the T-junction microchannels could be formed. By changes in the surfactant concentration, the interfacial tension and the wetting ability varied, and the disordered or ordered two-phase flow patterns could be controlled. Evolutions of the contact angle of the oil in contact with the wall surface were explained by the adsorption of surfactant molecules to the solid-liquid interface. The increase of continuous phase flow rate and viscosity resulted in the decrease of the droplet size, and the droplet size was correlated with capillary number Ca. By comparing the variation range of drop size using the two methods, it was found that the method of perpendicular flow-induced droplet formation can control the drop size over a much wider range. (c) 2006 American Institute of Chemical Engineers.