This research reports a microfluidic device for producing small droplets via a microorifice and a T-junction structure. The orifice is fabricated using an isotropic undercut etching process of amorphous glass materials. Since the equivalent hydraulic diameter of the produced microorifice can be as small as 1.1？μm, the microdevice can easily produce droplets of the size smaller than 10？μm in diameter. In addition, a permanent hydrophobic coating technique is also applied to modify the main channel to be hydrophobic to enhance the formation of water-based droplets. Experimental results show that the developed microfluidic chip with the ultrasmall orifice can steadily produce water-in-oil droplets with different sizes. Uniform water-in-oil droplets with the size from 60？μm to 6.5？μm in diameter can be formed by adjusting the flow rate ratio of the continuous phase and the disperse phases from 1 to 7. Moreover, curable linear polymer of chitosan droplets with the size smaller than 100？μm can also be successfully produced using the developed microchip device. The microfluidic T-junction with a micro-orifice developed in the present study provides a simple yet efficient way to produce various droplets of different sizes. 1. Introduction Droplets of the size in micrometer or nanometer for advanced pharmaceutical and biomedical applications have become a popular research field in the recent years [1]. The production of medicine embedded microemulsion droplets is one of the important topics in this research field [2]. Droplet-based microfluidic devices have played important roles in the formation of various functional droplets in a high-throughput and high precision way [3]. A number of so-called “emulsification” techniques including T-junction shearing [4–7], flow focus necking [8, 9], and pneumatic pumping [10] have been reported to generate droplets in a continuous manner. Over the reported microfluidic devices for droplets formation, micro-T-junction generator is the most popular scheme for producing droplets in devices. This droplet formation technique relies on the inherence properties of the employed liquids. T-junction microchannel devices provide a sharp edge where the continuous liquid phase cuts the dispersed liquid phase into small droplets by shearing force. The surfactant between the two immiscible liquids prevents the combination of these two liquids. Droplets with the size from tens to hundreds micrometers can be easily formed with this simple microfluidic structure. In general, the operation of this kind of microfluidic device depends on the
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