Tailoring re-entrant geometry in inverse colloidal monolayers to control surface wettability

Abstract

Controlling the microscopic wetting state of a liquid in contact with a structured surface is the basis for the design of liquid repellent as well as anti-fogging coatings by preventing or enabling a given liquid to infiltrate the surface structures. Similarly, a liquid can be confined to designated surface areas by locally controlling the wetting state, with applications ranging from liquid transport on a surface to creating tailored microenvironments for cell culture or chemical synthesis. The control of the wetting of a low-surfacetension liquid is substantially more difficult compared to water and requires surface structures with overhanging features, known as re-entrant geometries. Here, we use colloidal self-assembly and templating to create two-dimensional nanopore arrays with tailored re-entrant geometry. These pore arrays, termed inverse monolayers, are prepared by backfilling a sacrificial colloidal monolayer with a silica sol-gel precursor material. Varying the precursor concentration enables us to control the degree to which the colloids are embedded into the silica matrix. Upon calcination, nanopores with different opening angles result. The pore opening angle directly correlates with the re-entrant curvature of the surface nanostructures and can be used to control the macroscopic wetting behavior of a liquid sitting on the surface structures. We characterize the wetting of various liquids by static and dynamic contact angles and find correlation between the experimental results and theoretical predictions of the wetting state based on simple geometric considerations. We demonstrate the creation of omniphobic surface coatings that support Cassie-Baxter wetting states for liquids with low surface tensions, including octane (g ¼ 21.7 mN m À1). We further use photolithography to spatially confine such low-surface-tension liquids to desired areas of the substrate with high accuracy.

Molecular Imprinting of Bisphenol A on Silica Skeleton and Gold Pinhole Surfaces in 2D Colloidal Inverse Opal through Thermal Graft Copolymerization

“…A silica sol-gel precursor solution was prepared following the previously reported procedure [ 23 ]. As the pre-hydrolyzation step, TEOS (5.32 mL), absolute ethanol (9.5 mL), and 0.1 N HCl aqueous solution (5 mL) were injected in a nitrogen-filled glass bottle and slightly stirred for 1 h. Absolute ethanol (17.83 mL) was added to the mixture and stirred for over an hour again.…”

Recent Progress in Preparation and Anti-Icing Applications of Superhydrophobic Coatings

“…Hou et al copied the surface microstructure of a filter paper through the template processing technology and prepared superhydrophobic PTFE surface [102]. Vogel et al used colloidal self-assembly and templating methods to create two-dimensional nanopore arrays with precisely adjustable re-entrant curvatures (Figure 10a) [103]. The simple nanoscale architecture, prepared by backfilling a colloidal monolayer with a variation of concentration of sol-gel precursor, enables us to rationally tailor the macroscopic wetting properties, even for low-surface-tension liquids (as shown in Figure 10b…”

Sticky Situations: Bacterial Attachment Deciphered by Interferometry of Silicon Microstructures

“…During this stage, the Si surface is introduced to an aqueous solution of MB and coated with ions from the surrounding medium -assuming sufficient wetting. The introduction of a liquid to a surface brings about two key players involved in bacteria cell attachmentthe first being wettability, [18] which is partially dependent on the structural topology of the surface [42] ; and the second being surface charge, which is dependent on the surface chemistry.…”