Coaxial Capillary Microfluidic Chips Modified with Poly(vinyl alcohol) for the Long-term Production of Uniform Oil Droplets

Coaxially aligned microfluidic devices were fabricated using a round silica microcapillary and a square glass capillary with different inner diameters (200 and 300 µm). The inner wall of the square glass capillary was modified with poly(vinyl alcohol) (PVA) through plasma treatment to provide a hydrophilic surface. The microfluidic device consisting of the glass capillary with the smaller inner diameter demonstrated uniform oil droplet formation, compared to that with the larger inner diameter. The production of uniform droplets and microspheres originated from the coaxial alignment of the silica microcapillary with the square glass capillary. The glass substrate treated by plasma and PVA modification exhibited a hydrophilic surface, resulting in more stable uniform droplet formation for 6 h. The microfluidic device with PVA-coated glass capillary can be potentially used as a platform for the reproducible and reliable production of uniform oil droplets for a long period of time.