Microfabrication (Hot-Embossing) of COC Microfluidic Devices: Effect of Norbornene Content on Replication Fidelity and Surface Modification by UV-Photografting

Abstract

The fabrication of polymer based microfluidic devices using the hot embossing technique and their surface modification for easy fluid flow through the devices has been a growing field of research. During hot embossing, the replication fidelity on polymer substrate not only depends on the processing parameters such as temperature, pressure and time but also on their chemical structure which affects their thermo-dependent viscoelastic properties. For copolymers such as cyclic olefin copolymer (COC) which comprises ethylene and norbornene units, such properties depend on their relative ethylene and norbornene content. We report in this paper, a systematic study of replication fidelity and surface modification on COC polymer with varying norbornene content from 65 to 82 wt%. Replication fidelity which includes the surface morphology and cross-section profiles of the microchannel were characterized using SEM and Confocal microscope respectively. The modified surface was evaluated using Fourier transform infrared spectroscopy (FTIR spectroscopy) and water contact angle measurement. It was observed that in hot embossing, higher norbornene content contributed to good replication fidelity at identical experimental conditions. Furthermore, it was observed that with increase in norbornene content, the grafting efficiency decreases resulting in poor surface modification.