Conformal, Amine-Functionalized Thin Films by Initiated Chemical Vapor Deposition (iCVD) for Hydrolytically Stable Microfluidic Devices

Poly(4-aminostyrene) (PAS) thin films were synthesized via initiated chemical vapor deposition (iCVD) with tert-butyl peroxide as the initiator, representing the first time that a library of iCVD functional groups has been extended to amine moieties. The retention of the pendent amine chemical functionality was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) reveals that the iCVD PAS coatings are conformal over nonplanar structures. Fluorescence microscopy and photoluminescence of quantum dot functionalized surfaces confirm that the reactive amine functional group density at the surface of iCVD PAS is ∼1 order of magnitude greater than for films grown by plasma-enhanced chemical vapor deposition (PECVD). The higher amine density of the iCVD films enables the formation of a robust nanoadhesive with complementary epoxy functional groups. Prototype microfluidic structures were fabricated using the low-temperature (50 °C) and zero-outgassing reaction between the amine groups in iCVD PAS and the epoxy groups in iCVD poly(glycidyl methacrylate) (PGMA). Bonded devices able to withstand >150 psi were achieved by combining polydimethylsiloxane (PDMS) and a variety of other materials including Si wafers, polycarbonate (PC), glass, polyethylene terephthalate (PET), polyethylene (PE), polyacrylate (PA), and cyclic olefin copolymer (COC). Additionally, the all-iCVD nanoadhesive bonding process displays high resistance against hydrolytic degradation (>2 weeks). Within the channels of the bonded devices, the epoxy and amine groups remain available for subsequent functionalization.