(664c) Functional Polymeric Nanocoatings for Microfluidic Devices

Modification with specific organic groups is critical for controlling the functionality of the surface. The organic functional groups can be utilized to tune surface energy, to enable subsequent chemical attachment of desirable molecules, or to covalently bind micro- or nanoparticles to the surface. The initiated chemical vapor deposition (iCVD) method has shown great promise as a surface modification technique, and it has successfully been used to create many distinct homopolymers, random copolymers, and alternating copolymers using free radical polymerization. It is chemically comparable to solution-phase polymerization but is environmentally friendly, able to achieve good conformality, and able to maintain the chemical functionality in the monomers.

Amine-functionalized iCVD surfaces have not yet been reported. Selection of a monomer is challenging because many candidates have low vapor pressures as a result of hydrogen bonding between amine groups. In this work, poly(4-aminostyrene) (PAS) thin films were synthesized via 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 photo-electron 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 were able to withstand pressure higher than 150 psi. While the traditional plasma sealing methods are specific for sealing glass or Si wafers to polydimethylsiloxane (PDMS), this new bonding method is compatible with a wide variety of polymeric materials, including polycarbonate (PC), polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS), 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.