Versatile and Selective Fluorination of the Surface of Polymeric Materials After Stereolithography 3D Printing

Abstract

With the\nmicrofluidics community embracing 3D resin printing as a rapid fabrication\nmethod, controlling surface chemistry has emerged as a new challenge.\nFluorination of 3D printed surfaces is highly desirable in many applications\ndue to chemical inertness, low friction coefficients, anti-fouling properties\nand the potential for selective hydrophobic patterning. Despite sporadic\nreports, silanization methods have not been optimized for covalent bonding with\npolymeric resins. As a case study, we tested the silanization of a commercially\navailable (meth)acrylate-based resin (BV-007A) with a fluoroalkyl\ntrichlorosilane. Interestingly, plasma oxidation was unnecessary for silanization\nof this resin, and indeed was ineffective. Solvent-based deposition in a\nfluorinated oil (FC-40) generated significantly higher contact angles than\ndeposition in ethanol or gas-phase deposition, yielding hydrophobic surfaces with\ncontact angle > 110˚ under optimized conditions. Attenuated Total Reflectance-Fourier\nTransform Infrared (ATR-FTIR) spectroscopy indicated that the increase in\ncontact angle correlated with consumption of a carbonyl moiety, suggesting\ncovalent bonding of the silane without plasma oxidation. Consistent with a\ncovalent bond, the silanization was resistant to mechanical damage and\nhydrolysis in methanol, and was stable over long-term storage. When tested on a\nsuite of photocrosslinkable resins, this silanization protocol generated highly\nhydrophobic surfaces (contact angle > 110˚) on three resins and moderate\nhydrophobicity (90 – 100˚) on the remainder. Selective patterning of hydrophobic regions in\nan open 3D-printed microchannel was possible in combination with simple masking\ntechniques. Thus, this facile\nfluorination strategy is expected to be applicable\nfor resin-printed materials in a variety of contexts including micropatterning\nand multiphase microfluidics.