Effects of fabrication process parameters on the properties of cyclic olefin copolymer microfluidic devices

Among the materials used for fabricating microfluidic devices, plastics have been increasingly employed in the past few years. Although several methods for fabricating plastic devices have appeared in the literature, reports typically indicate one set of conditions that yield functional devices; little data are available detailing how results are affected by their changes in the process variables. We report in this paper a systematic study of fabrication process parameters including compression rate, molding temperature, and the force used by a hydraulic press, as well as their effects on the device properties. Using cyclic olefin copolymers as the molding material, we found that the device thickness decreased when the molding temperature and compression force increased. Fidelity in the pattern transfer from a master to a device was confirmed by the reproduction of nanostructures and channel depth/shape. Pattern transfer fidelity appeared to be independent of the molding temperature and compression force, at least in the range of conditions we investigated. Stress whitening (or crazing) on the device surface was found to be related to the molding temperature and the cooling rate of the mold/device assembly. The bond strength between the layers of a laminated device was determined to be a function of the lamination temperature. In addition, we demonstrated the utility of a plastic microfluidic device by separating proteins.