Improvement of thermal bond strength and surface properties of Cyclic Olefin Copolymer (COC) based microfluidic device using the photo-grafting technique

This paper reports on the development and application of a permanent surface modification technique (photo-grafting) as an improved method for bonding COC (TOPAS) microfluidic substrates with a cover plate without affecting the channel integrity. This technique not only helps to increase the bond strength of the original device but also makes the surface hydrophilic which is essential for quick fluid flow while passing analytes through the device. The bond strength of the modified and unmodified chips was measured using the tensile and peel tests. It was observed that the bond strength of the modified chips has increased approximately 6 times to 1.18 (±0.08) MPa compared to 0.21 (±0.05) MPa for the unmodified chip. The modified surface was evaluated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and water contact angle measurement. The contact angle of the modified surface decreased to 20 ± 5° from 85 ± 3° for the untreated substrate. Scanning electron microscope and confocal microscope examinations of cross-sectional profiles of the bonded chips indicated that the integrity of the channel features was successfully preserved.