Preparation of highly uniform single and double emulsions with microfluidic chips modified by region-selective UV irradiation

A novel region-selective hydrophilic modification approach by UV irradiation was used to change the surface property in PDMS-based microfluidic chip. The surface properties of microchannels before and after modification were characterized by contact angle measurement and atomic force microscope. Thereafter, microfluidic chip region-selectively modified by this method was applied to prepare highly uniform single and double emulsions. The results demonstrated that in the un-exposed region, original hydrophobic PDMS surface tended to be very coarse and hydrophobic with contact angle 101° after photoinitiator solution treatment. But in the UV-exposed region, poly(acrylic acid) was coated on the surface, leading to a hydrophilic surface with contact angle 62°. In addition, those hydrophilic and hydrophobic features were able to maintain at least for 30 d. Using the modified microfluidic chips, three kinds of highly uniform O/W single droplets, soybean oil, trimethylolpropane triacrylate and fluorocarbon oil, were prepared with coefficient variation (CV) below 3%. Uniform W/O/W double emulsions were also successfully prepared with CV of the outer and inner diameters at 3.5% and 2.9%, respectively.