Enabling Organosilicon Chemistries on Inert Polymer Surfaces with a Vapor-Deposited Silica Layer

Abstract

Given the large surface area-to-volume ratios commonly encountered in microfluidics applications, the ability to engineer the chemical properties of surfaces encountered in these applications is critically important. However, as various polymers are rapidly replacing glass and silicon as the chosen materials for microfluidics devices, the ability to easily modify the surface chemistry has been diminished by the relatively inert nature of some commonly employed polymer surfaces, such as poly(methyl methacrylate) (PMMA), polystyrene, and polydimethylsiloxane (PDMS). This paper describes the low-temperature, vapor-phase deposition of robust silica layers to PMMA, polystyrene, and PDMS surfaces, which enables the functionalization of these surfaces by standard organosilane chemistries. Attenuated total reflection infrared spectroscopy, contact angle goniometry, ellipsometry, and atomic force microscopy are used to characterize the silica layers that form on these surfaces. Aqueous immersion experiments indicate that the silica layer has excellent stability in aqueous environments, which is a prerequisite for microfluidics applications, but for PMMA surfaces, low adhesion of the silica layer to the underlying substrate is problematic. For PDMS substrates, the presence of the silica layer helps to slow the process of hydrophobic recovery, which is an additional advantage.

Photo-initiated chemical vapor deposition of thin films using syngas for the functionalization of surfaces at room temperature and near-atmospheric pressure

“…For that reason, the water contact angles were measured in the hour following the deposition. According to Anderson and Ashurst hydrophobic recovery would be due to the migration of bulk material to the surface [26]. On the other hand, Wertheimer et al a rm that hydrophobic recovery was due to hydrogen molecules which rotate inward caused by the attraction of hydrogen bond [27].…”

Selective Fluorination of the Surface of Polymeric Materials after Stereolithography 3D Printing

“…35 In some cases, the printed polymer had to be coated with a layer of silica to enable silanization. 36,37 To date, there has been little testing of the conditions required for direct fluoroalkyl silanization of resin-printed pieces, nor characterization of the hydrophobicity and stability of the silanized surface.…”

“…Historically, polymers have been chemically modified primarily by strategies such as wet etching, plasma or corona treatment, or coatings, rather than direct silanization. − Extensive surface oxidation is usually required to generate enough silane-reactive functional groups (e.g., hydroxyls) at the polymer surface, and not all polymers can withstand such treatment, as they may degrade after plasma exposure. ,,,, So far, there have been sporadic reports of silanization of resin 3D-printed microfluidic devices, e.g., to fluorinate 3D-printed molds for PDMS and to attach reactive functionalities for bonding of 3D-printed pieces . In some cases, the printed polymer had to be coated with a layer of silica to enable silanization. , To date, there has been little testing of the conditions required for direct fluoroalkyl silanization of resin-printed pieces, nor characterization of the hydrophobicity and stability of the silanized surface.…”

Surface Modification of Droplet Polymeric Microfluidic Devices for the Stable and Continuous Generation of Aqueous Droplets

“…Hence, reactions of silanes with polymer surfaces are most commonly carried out in the gas phase. 25, 29-31 However, gas-phase reactions can often lead to multilayers of silanes, 30 thereby leading to a lack of control over the thickness of the silane layer.…”