Study of the Stability and Hydrophilicity of Plasma-Modified Microfluidic Materials

Abstract

Polymers among new classes of materials such as polydimethylsiloxane (PDMS), cyclic olefin copolymer (COC), Norland optical adhesive (NOA), and THV (fluoropolymer) were evaluated as surface-modified microfluidic materials, including investigating the incorporation of silicalike functional groups onto these surfaces. The functionalization of these materials was performed using a hybrid reactor equipped with magnetron sputtering using a silica target and with a PECVD apparatus starting from hexamethyldisiloxane as a chemical precursor. Coated microfluidic materials were then evaluated in terms of wettability, stability, composition, and structure. The deposited coatings were proved to be stable up to 2 month in air and water storage for these materials, with COC providing the most stable substrate. (7 of 15) 1600034 www.plasma-polymers.org PECVD: 150 W plasma discharge power, 4 min deposition time, 150 sccm oxygen flow rate, and 0.3 mbar precursor pressure.Sputtering: 150 W plasma discharge power, 60 min deposition time, 30 sccm Ar flow rate, and 150 sccm O 2 flow rate. (11 of 15) 1600034 www.plasma-polymers.org PECVD: 150 W plasma discharge power, 4 min deposition time, 150 sccm oxygen flow rate, and 0.3 mbar precursor pressure. Sputtering: 150 W plasma discharge power, 60 min deposition time, 30 sccm Ar flow rate, and 150 sccm O 2 flow rate.

Surface functionalization of cyclic olefin copolymer by plasma‐enhanced chemical vapor deposition using atmospheric pressure plasma jet for microfluidic applications

“…Untreated COC surfaces present an ATR‐FTIR spectrum (Figure a) with absorption bands located at 2,947 and 2,868 cm −1 , which are assigned to carbon/hydrogen stretching vibration modes of –CH 2 and –CH 3 groups from the polymer backbone. The band around 1,456 cm −1 corresponds to the wagging mode of –CH 3 groups . The WCA measurements of untreated COC plate (95 ± 1°) confirmed the hydrophobic properties of the polymer .…”

“…When treated with the plasma jet, COC plates were attached with carbon tape on a holder. So as to remove eventual low molecular weight fragments at the topmost COC surface layer, they were pretreated by air plasma at atmospheric pressure (APAP) at 80 kHz (987 W, 35 L/min air) with a nozzle speed of 150 mm/s. Indeed, oxygen radicals and excited molecules produce volatile organic and inorganics compounds such as CO, CO 2 , H 2 O molecules, eliminating low molecular weight oxidized fragments.…”

“…This low‐pressure plasma process consists of the fragmentation of a precursor inside the gas plasma. Organosilicon–oxygen mixtures are widely used to generate thin silica film deposition, notably for microfluidic applications . The thin silica layer confers hydrophilic properties allowing the generation of a controlled electro‐osmotic flow for electrokinetic separations inside COC microchannels .…”

“…The thin silica layer confers hydrophilic properties allowing the generation of a controlled electro‐osmotic flow for electrokinetic separations inside COC microchannels . Moreover, the presence of reactive chemical functions, such as silanol groups (SiOH), due to plasma polymerization of organosilicon precursors, could allow the grafting of several chemical entities . Da Silva et al have shown the possibility to deposit by PECVD at low pressure thin layers of silica (700 nm thickness) on COC surface.…”

“…Moreover, the presence of reactive chemical functions, such as silanol groups (SiOH), due to plasma polymerization of organosilicon precursors, could allow the grafting of several chemical entities . Da Silva et al have shown the possibility to deposit by PECVD at low pressure thin layers of silica (700 nm thickness) on COC surface. This layer was characterized by water contact angle (WCA), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy (FTIR), and ellipsometry measurements, showing the presence of a silica film on the COC substrate.…”