Modifying Base Metal Substrates to Exhibit Universal Non‐Wettability: Emulating Biology and Going Further

Abstract

The design and fabrication of surfaces that are not wetted either by water or oil holds much significance for the energy infrastructure, particularly where corrosion represents a significant problem and cleaning, maintenance, and repair of containers, pipelines, and processing equipment is difficult or poses safety hazards. Nature has numerous examples of surfaces that resist fouling by repelling liquid (especially water) droplets. Designing a surface that is not wetted by low‐surface‐tension liquids such as hydrocarbons is a considerably more difficult task that is beyond the capabilities of most natural systems since the cohesive forces within such liquids are low and most interfacial interactions induce the spreading of oil droplets. A combination of hierarchical texturation, reentrant curvature, and low surface energy is thought to be necessary to design omniphobic surfaces. However, such surfaces are often constructed from polymers and thus prone to thermal degradation. In this contribution, we illustrate the modular design and development of a biomimetic architecture incorporating micro‐ and nanoscale texturation on etched carbon steel. Etching of the steel substrate endows microscale roughness; the substrate is further coated with ZnO nanotetrapods to define nanoscale texturation and further modified to expose pendant fluorous groups. The highly textured substrates exhibit simultaneous superhydrophobic and superoleophobic behavior. The utilization of ZnO nanotetrapods with protruding arms gives rise to a nanotextured morphology regardless of the specific orientation of the nanostructures and allows for the trapping of air pockets, thereby suspending liquid droplets as per the Cassie–Baxter mode. The textured ceramic/metal surfaces are stable up to high temperatures and are well adhered to the metal substrate upon application of a conformal amorphous SiO 2 coating. The incorporation of multiple design elements—microscale roughness, nanotexturation, a “cementing” layer, and surface modification with low‐energy pendant perfluorinated chains—provides considerable versatility and tunability for specific liquid‐handling conditions. The strategy described here is generalizable to other modes of texturation and surface modification and can be broadly adapted to prevent wettability of a surface by a specific liquid, thereby allowing for protection of components exposed to corrosive fluid environments.

Separation of Viscous Oil Emulsions Using Three-Dimensional Nanotetrapodal ZnO Membranes

“…ZnO tetrapods were prepared based on the rapid oxidation of metallic Zn foils in air as described in our previous work. ,− Briefly, Zn metal sheets (0.2 mm in thickness) were cut into substrates with approximate dimensions of 3 mm × 3 mm. The diced Zn substrates were then placed onto a boatlike stainless steel mesh and placed within a 1 in.…”

Asphaltene Microencapsulation of Bitumen as a Means of Solid-Phase Transport

“…Viscous oil represents a major hydrocarbon reserve with massive deposits concentrated in Alberta and Venezuela. The unfavorable rheological properties of heavy crude oil and bitumen greatly constrain their effective utilization, posing a distinctive set of challenges during extraction, midstream transportation from wellhead to geographically distant refineries, and eventual processing to liquid fuels or chemical feedstock. ,− Midstream transportation of these highly viscous fluids relies on an extensive thermal jacketing infrastructure for pipelines and containers and necessitates the addition of diluents, primarily low-molecular-weight hydrocarbons, to improve flow properties. In addition to the potential for environmental contamination resulting from spillage, fluid transport is energy-intensive, requires the unproductive flow of large volumes of expensive diluents across North America, and is plagued by product losses during transportation .…”

“…However, pipelines designed for light and medium crude oils are ill-suited for heavy oils such as bitumen given the rheological challenges, high asphaltene content, paraffin deposition, and corrosion issues arising from remnant brine or salts produced during typical extraction processes . Efforts to improve bitumen pipeline transportation have focused on optimizing pumping requirements, design of surface coatings that glide viscous oils, ,, modification of bitumen viscosity through separation of asphaltenes before transportation, solubilization of bitumen in aromatic solvents, and de-emulsification to reduce the brine content . While beneficial to promoting flow, these approaches do not address the fundamental issues of spillage and environmental contamination.…”

Three-Dimensional Inverse Opal TiO2 Coatings to Enable the Gliding of Viscous Oils

“…Fossil fuels continue to play a dominant role in meeting increasing global energy needs and are of central importance as the primary feedstock of the chemical and asphalt industries . An increasing proportion of extracted fuels is sourced from unconventional geological deposits, such as heavy crude oil and natural bitumen. − The high viscosity of heavy crude and bitumen presents a substantial challenge in extractive, midstream transportation, and refinery processing operations. − From the perspective of midstream operations, rheological challenges associated with heavy crude oil exact a heavy toll in terms of energy expenditure and processing costs as a result of the need for thermal jacketing and dilution with low molecular weight hydrocarbons. Furthermore, the maintenance and cleaning of railcars, tankers, and trucks used to transport heavy oils incurs a considerable cost, results in product losses from unrecovered residues, and engenders safety hazards.…”

“…For instance, liquid-impregnated coatings show promising performance but are readily damaged and difficult to scale; lithographically patterned architectures provide precise control of re-entrant curvature, but their elaboration to macroscopic scales remains challenging; polymeric coatings, such as block copolymers, enable definition of tailored chemical domains but have inadequate thermal stability and are prone to fouling. In previous work, we have demonstrated the promise of ceramic/metal coatings comprising ZnO tetrapods sprayed onto metal mesh surfaces; surface functionalization of the tetrapods yields hydrophobic/oleophobic, hydrophilic/oleophobic, or hydrophobic/oleophilic , character, enabling applications ranging from gliding of viscous oils to the separation of recalcitrant water/oil emulsions. The ZnO tetrapods serve to amplify the intrinsic wettability of the surface monolayers and yield 3D interconnected plastronic architectures that extend into the pores of the metal meshes, with the meshes additionally providing periodic micron-scale texture.…”