Self‐Assembling, Bioinspired Wax Crystalline Surfaces with Time‐Dependent Wettability

Abstract

One of the most fascinating properties of materials in nature is the superhydrophobic and self‐cleaning capabilities of different plant surfaces. This is usually achieved by the hydrophobic cuticles that are made of cutin and contain wax crystals both within them and on their surfaces. Here, bioinspired n‐hexatriacontane wax films are deposited via thermal evaporation and it is shown that the surface evolves in time via self‐assembly. This leads to a dramatic change in the wetting properties with a transition from hydrophobic to superhydrophobic characteristics, which takes place within several days at room temperature. This phenomenon is investigated and strain‐induced recrystallization is proposed to be the mechanism for it. This work could become the basis for the inspiration and production of tuned, time‐dependant, temperature‐sensitive, variable‐wettability surfaces.

Lubricant-infused micro/nano-structured surfaces with tunable dynamic omniphobicity at high temperatures

“…6,7 Other approaches to generating re-entry geometries that achieve omniphobicity were later demonstrated. [8][9][10] It was also shown that small liquid droplets can bounce off an extremely hot superhydrophobic surface reminiscent of the Leidenfrost effect, provided that the heat transfer between the solid and liquid is sufficient to generate a vapor layer, which can only occur when the temperature of the solid substrate T solid is significantly above the liquid's boiling point (T solid > 150°C for water).…”

Superhydrophobic Coating of European Oak (Quercus robur), European Larch (Larix decidua), and Scots Pine (Pinus sylvestris) Wood Surfaces

“…The wax was evaporated at a temperature (T) of 200 °C by applying pulses of an electric current. The temperature of wax evaporation was obtained from experimental study of Pechook and Pokroy (2012). The pressure in the chamber was 10 -4 mbar.…”

“…The melting temperature of n-hexatriacontane is T = 76 °C, and the wax doesn´t decompose (Matacotta and Ottaviani 1995). Methods of wax evaporation were obtained from the studies of (Pechook a Pokroy 2012;Bhushan et al 2009). …”

“…The formation and the process of wax crystal creation is described well in several papers (Bhushan et al 2009;Pechook and Pokroy 2012). However, these studies focused only on the process of wax self-assembly on inert and flat surfaces.…”

“…However, new developments show that other considerations for CA and CA hysteresis may need to be taken as well. Gao and McCarthy suggested that the contact line model is better approach to predict superhydrophobicity of surfaces McCarthy 2007, 2009 (Koch et al 2009a;Niemietz et al 2009;Cao 2010;Guo and Wang 2010;Bhushan and Jung 2011;Pechook and Pokroy 2012). The study of Wang et al (2013) showed combined effects of the spherical silica nanoparticles (roughness increment) and their hydrophobization with HDTMS as a promising approach for surface treatment of wood.…”