Composite Fluorocarbon Membranes by Surface-Initiated Polymerization from Nanoporous Gold-Coated Alumina

Abstract

This manuscript describes the versatile fabrication and characterization of a novel composite membrane that consists of a porous alumina support, a 100 nm thick nanoporous gold coating, and a selective poly(5-(perfluorohexyl)norbornene) (pNBF6) polymer that can be grown exclusively from the nanoporous gold or throughout the membrane. Integration of the three materials is achieved by means of silane and thiol chemistry, and the use of surface-initiated ring-opening metathesis polymerization (SI-ROMP) to grow the pNBF6. The use of SI-ROMP allows tailoring of the extent of polymerization of pNBF6 throughout the structure by varying polymerization time. Scanning electron microscopy (SEM) images indicate that the thin polymer films cover the structure entirely. Cross-sectional SEM images of the membrane not only corroborate growth of the pNBF6 polymer within both the porous alumina and the nanoporous gold coating but also show the growth of a pNBF6 layer between these porous substrates that lifts the nanoporous gold coating away from the alumina. Advancing contact angle (θ(A)) measurements show that the surfaces of these composite membranes exhibit both hydrophobic (θ(A) = 121-129)° and oleophobic (θ(A) = 69-74)° behavior due to the fluorocarbon side chains of the pNBF6 polymer that dominate the surface. Results from electrochemical impedance spectroscopy (EIS) confirm that the membranes provide effective barriers to aqueous ions, as evidenced by a resistive impedance on the order of 1 × 10(7) Ω cm(2). Sulfonation of the polymer backbone substantially enhances ion transport through the composite membrane, as indicated by a 40-60 fold reduction in resistive impedance. Ion transport and selectivity of the membrane change by regulating the polymerization time. The fluorinated nature of the sulfonated polymer renders the membrane selective toward molecules with similar chemical characteristics.

Preparation of a biomimetic superhydrophobic ZnO coating on an X90 pipeline steel surface

“…For the past few years, researchers have focused their attention on producing superhydrophobic surfaces on various materials, for example, fibers, 14 SiO 2 , 15 TiO 2 , 16 brass, 17 Al, 18 and Zn. 19 However, to the best of our knowledge, it is rare to obtain a superhydrophobic surface on a steel surface, let alone pipeline steel.…”

Surface-Initiated Ring-Opening Metathesis Polymerization (SI-ROMP): History, General Features, and Applications in Surface Engineering with Polymer Brushes

“…Postpolymerization functionalizations have also been adopted to tune the properties of the surface-tethered polymers. For ROMP polymers, the olefin groups in the backbone are often used for further functionalization, one of which is sulfonation [34,91]. According to the method reported by Berron et al in 2008, the polymer film generated by SI-ROMP was exposed to a dichloromethane solution of acetyl sulfate, which sulfonated the olefin groups in the polymer chains.…”

“…By rendering a surface hydrophobic, SI-ROMP could be used to modify the wettability of the channels in microfluidic devices [96][97][98] to introduce flow regulations, such as hydrophobic capillary stop valves. Also, previous researches carried out SI-ROMP of fluorinated norbornenes (NBFn) to graft a hydrophobic and oleophobic polymer film [25,91]. Surfaces that are neither hydrophilic nor oleophilic are referred to as "ambiguous" and could possess antibiofouling properties due to the weakening of both hydrophilic and hydrophobic interactions [99].…”

Copolymerization of a Catechol and a Diamine as a Versatile Polydopamine-Like Platform for Surface Functionalization: The Case of a Hydrophobic Coating

“…Nevertheless, this approach usually requires chemical specificity between substrate and anchoring group. For example, thiols are useful for noble metals such as gold [2,3,4,5,6], platinum [7,8,9,10] and palladium [7,11], phosphates and phosphonates for metal oxides [12,13,14,15] and silanes for hydroxyl-bearing materials such as cellulose [16,17] and silicon oxides [18,19,20,21,22], zinc oxides [23,24], iron oxides [25,26], boron [27], and alumina [6] among others. In order to overcome this limitation, several research groups have drawn inspiration from mussel adhesive proteins, since it is known that they are able to strongly stick onto virtually any kind of surface, thus being usable as models for universal anchoring elements [28,29,30].…”