Bioinspired Metal-Intermetallic Laminated Composites for the Fabrication of Superhydrophobic Surfaces with Responsive Wettability

Fabrication of a Bionic Superhydrophobic Surface with Photothermal and Electrothermal Performance for All-Weather Anti-Icing

All-weather anti-icing/deicing materials with photothermal and electrothermal functionalities are of substantial significance to solve the problem of ice accumulation. In this work, polypropylene with bionic rose petal micro-/nanostructures and conductive carbon black (CB) (Bionic PP/CB) is fabricated by a template method. The template is obtained by replicating fresh rose petals with phenolic resin and spraying conductive CB. The contact angle of Bionic PP/CB is up to 162.5°, and the rolling angle is as low as 2.5°. The superhydrophobicity of Bionic PP/CB is theoretically analyzed by calculating the liquid-air contact area and surface energy. The ice adhesion strength of the surface is as low as 6.06 kPa. Due to the incorporation of CB, the effects of ultraviolet light, acid immersion, and friction on the superhydrophobic properties can be effectively mitigated. The photothermal performance of Bionic PP/CB has been improved, and it can be used for photothermal anti-icing. CB can form conductive paths on the surface to achieve electrothermal conversion, which can compensate for insufficient sunlight. The temperature of Bionic PP/CB can reach 132 °C at 15 V, which can greatly shorten the melting time and effectively prevent surface frosting. Leveraging the synergistic effects of photothermal and electrothermal functionalities, the surface combined with bionic micro-/nanostructures and CB has promising applications in the fabrication of low-cost, energy-efficient, all-weather anti-icing/deicing materials.

Defect by design: Harnessing the "petal effect" for advanced hydrophobic surface applications

HYPOTHESIS

In the interfacial wetting boundary, the superhydrophobic surface is often damaged, and the anisotropic wettability of its surface has attracted many researchers' attention. The "petal effect" surface has typical anisotropic wettability. We predict that under the dual conditions of structural defects and high impact velocity, the "petal effect" becomes more adhesive on the surface.

EXPERIMENTS

This study refers to the droplet state on rose petals, structural defects were constructed on the superhydrophobic surface. This paper studies the influence of macro-structural defects on the wettability change from natural to bionic "lotus effect" to "petal effect" in both static and dynamic angles.

FINDINGS

Macro defects significantly change the static contact angle of the superhydrophobic surface. The higher the impact velocity of the droplet, the higher the energy dissipation of the "petal effect" surface (DSHS), which improves the adhesion of the surface to the droplet and prolongs the contact time. It is found that the defect structure and high impact velocity will directly affect the deposition and desorption of droplets on the superhydrophobic surface, and they are both essential. This wetting dynamic law is very likely to be helpful in the quantitative design of defect structure scale for dynamic desorption of droplets on superhydrophobic surfaces.

Surface Modification, Topographic Design and Applications of Superhydrophobic Systems

Superhydrophobic surfaces with expanded wetting behaviors, like tunable adhesion, hybrid surface hydrophobicity and smart hydrophobic switching have attracted increasing attention due to their broad applications. Herein, the construction methods, mechanisms and advanced applications of special superhydrophobicity are reviewed, and hydro/superhydrophobic modifications are categorized and discussed based on their surface chemistry, and topographic design. The formation and maintenance of special superhydrophobicity in the metastable state are also examined and explored. In addition, particular attention is paid to the use of special wettability in various applications, such as membrane distillation, droplet-based electricity generators and anti-fogging surfaces. Finally, the challenges for practical applications and future research directions are discussed.

A Comprehensive Review of Wetting Transition Mechanism on the Surfaces of Microstructures from Theory and Testing Methods

Superhydrophobic surfaces have been widely employed in both fundamental research and industrial applications because of their self-cleaning, waterproof, and low-adhesion qualities. Maintaining the stability of the superhydrophobic state and avoiding water infiltration into the microstructure are the basis for realizing these characteristics, while the size, shape, and distribution of the heterogeneous microstructures affect both the static contact angle and the wetting transition mechanism. Here, we review various classical models of wettability, as well as the advanced models for the corrected static contact angle for heterogeneous surfaces, including the general roughness description, fractal theory description, re-entrant geometry description, and contact line description. Subsequently, we emphasize various wetting transition mechanisms on heterogeneous surfaces. The advanced testing strategies to investigate the wetting transition behavior will also be analyzed. In the end, future research priorities on the wetting transition mechanisms of heterogeneous surfaces are highlighted.

A strategy for preparing controllable, superhydrophobic, strongly sticky surfaces using SiO2@PVDF raspberry core-shell particles

In nature, wetting by water droplets on superhydrophobic materials is governed by the Cassie-Baxter or Wenzel models. Moreover, sticky properties, derived from these types of wettings, are required for a wide range of applications involving superhydrophobic materials. As a facile new strategy, a method employing a gaseous fluorine precursor to fabricate core-shell particles, comprising perfectly shaped fluorine shells with adjustable adhesive strength, is described in this paper. Silica was used as the hydrophilic core, while polyvinylidene fluoride (PVDF) was used for the hydrophobic shell coating, forming a raspberry-like shape. In addition, controlling the amount of PVDF coated on the silica surface enabled the water droplets to come into contact with both the PVDF of the shell and the silica of the core, thereby controlling both the superhydrophobicity and the adhesive strength. Thus, the synthesized particles formed a structured coating with controllable stickiness and contact angles of 131-165°. Furthermore, on surfaces with high adhesivity, the water droplets remained stable at tilt angles of 90° and 180° even under a strong centrifugal force, whereas on surfaces with low adhesivity, the water droplets slid off when the substrate was tilted at 4°.