Characterisation of an irreversible bonding process for COC–COC and COC–PDMS–COC sandwich structures and application to microvalves

Abstract

A novel technique for bonding heterogeneous cyclic olefin co-polymer (COC) to a thin poly(dimethylsiloxane) (PDMS) membrane is described. This improved bonding technique successfully achieved precise, well-controlled, low temperature bonding of microfluidic channels. Microchannel and fluid control patterns were embossed on a COC substrate by hot embossing technique first. The method uses aminopropyltriethoxysilane (APTES) and 3-glycidoxypropyltrimethoxysilane (GPTMS) in combination to create an irreversible bond between the two materials. The change in surface properties and the influence of different surface chemical groups on surface adhesion properties has been characterised by contact angle, surface energy measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM), revealing a change in morphology and surface roughness. A lower wettability was also observed along with a reduced hydrophobic recovery of the surfaces. Bonding efficiency of the devices was evaluated by interface evaluation of cross-sectioning, peel off tests and leak tests. In addition, the performance of the bonds achieved after different surface treatments has been compared showing that this technique results in a higher burst pressures than methods applying only oxygen plasma or APTES. Using optimised bonding conditions a robust, effective microvalve made from a PDMS membrane was fabricated and successful valve closing or opening are shown. Because of advantages of facile fabrication, low cost and biocompatibility, this hybrid device can be pave the way in many applications such as fluidic manipulation in portable and disposable microfluidic devices.