From Sticky to Slippery: Self-Functionalizing Lubricants for In Situ Fabrication of Liquid-Infused Surfaces

Abstract

Liquid-infused surfaces offer a versatile approach to create self-cleaning coatings. In such coatings, a thin film of a fluid lubricant homogeneously coats the substrate and thus prevents direct contact with a second, contaminating liquid. For stable repellency, the interfacial energies need to be controlled to ensure that the lubricant is not replaced by the contaminating liquid. Here, we introduce the concept of self-functionalizing lubricants. Functional molecular species that chemically match the lubricant but possess selective anchor groups are dissolved in the lubricant and self-adhere to the surface, forming the required surface chemistry in situ from within the applied lubricant layer. To add flexibility to the self-functionalizing concept, the substrate is first primed with a thin polydopamine base layer, which can be deposited to nearly any substrate material from aqueous solutions and retains reactivity toward electron-donating groups such as amines. The temporal progression of the in situ functionalization is investigated by ellipsometry and quartz crystal microbalance and correlated to macroscopic changes in contact angle and contact angle hysteresis. The flexibility of the approach is underlined by creating repellent coatings with various substrate/lubricant combinations. The prepared liquid-infused surfaces significantly reduce cement adhesion and provide easy-to-clean systems under real-world conditions on shoe soles.

Mechanical Stability of Liquid‐Infused Surfaces Based on Mussel‐Inspired Polydopamine Chemistry

“…The film thickness only marginally increased. While it was not possible to directly quantify the layer thickness of the deposited PDA film, previous results from our group of similar coating processes on flat substrates shows a PDA layer thickness of ≈25 nm, [36] in agreement with the visual impression of the SEM cross sections.…”

“…The composite structure was formed by the deposition of a uniform, porous layer of silica nanoparticles via dip‐coating [ 57 ] and subsequently coating the voids in the inorganic matrix (Figure 2d). [ 36 ] Scanning electron microscopy (SEM) cross‐sectional analyses (Figure 2e) show the porous nature of the initial porous silica substrate. A thickness of the porous coating of ≈100 nm can be seen.…”

“…[25] Optimization of this reaction pathway also enabled the combination of these reactions into two and one-step processes (Figure 1a). [27,36] As an example of the broad applicability of the PDA-based system in real-world scenarios, we previously coated elastomeric shoe soles, which showed a significant decrease in cement adhesion (Figure 1b, c) [36] compared to the uncoated reference.…”

Biomimetic Research for Applications Addressing Technical Environmental Protection

“…In addition, the application method ensures a possible scale-up. The project developed a sustainable, scalable, two-step process for synthetically mimicking the pitcher plant that is based entirely on aqueous dispersions, thus minimizing the use of harmful organic solvents in the coating process [ 31 , 32 ].…”

Dropwise Condensation in Ambient on a Depleted Lubricant-Infused Surface

“… 38 Apart from wetting ridges and condensate cloaking-induced depletion, 39 LIS undergo external shear 40 -driven drainage during relative motion between the LIS and any fluid. Consequently, numerous fabrication techniques have been reported to mitigate lubricant depletion and to extend the operational lifespan of LIS, such as, utilizing metal oxide nanowires and pores, 9 , 13 trapped air, 11 and self-functionalizing lubricants, 41 among others. However, after prolonged use of LIS, the lubricant layer on such surfaces depletes, causing drop pinning and decline in wetting behavior.…”