Thermomechanical Mechanisms of Reducing Ice Adhesion on Superhydrophobic Surfaces

Preparation and performance of anti-icing and deicing PF-POS@SiO2/CB photothermal superhydrophobic coatings for electrical insulators

Insulator string icing can cause flashovers or even blackouts in transmission systems and the existing mature deicing methods are usually costly or time consuming. So, in this research PF-POS@SiO2/CB superhydrophobic coatings (SiO2/CB-0, SiO2/CB-10, SiO2/CB-20, SiO2/CB-30, SiO2/CB-40 and SiO2/CB-50) with photothermal deicing and passive anti-icing properties were designed and prepared on the surface of two types of insulator materials (glass and ceramic) by using a simple spraying method. Then, the wettability properties, photothermal properties, and anti-icing/deicing properties of the coatings with the addition of different amounts of SiO2/CB were evaluated. PF-POS@SiO2/CB coatings with no less than 30 wt% of CB (carbon black) content simultaneously exhibit excellent passive anti-icing and deicing performance. For SiO2/CB-30, the water contact angle is as high as 164.9° and the rolling angle is as low as 3° because the combination of silica and carbon black nanoparticles gives the coating a micro/nanostructure and the low surface energy of 1H,1H,2H,2H-perfluorodecyltriethoxysilane leads to superhydrophobic properties, and the equilibrium temperature of the coating is up to 71.1 °C at 1 solar irradiation because of the photothermal effect of carbon black. The results of the analysis of anti-icing/deicing properties of the coatings to evaluate their potential for engineering applications demonstrate that it takes longer time for ice to form on the coated surface than on a substrate without coating, and the ice completely melts under sunlight after 10 min and falls off automatically by its weight for the addition of 30 wt% carbon black and above, showing excellent deicing performance. Both types of substrates show excellent adhesion with the superhydrophobic coating, which can be classified as class 1 based on the paint and varnish-cross-section test method, and the ceramic material exhibits better adhesion than the glass.

Fabrication and Experimental Study of Micro/Sub-Micro Porous Copper Coating for Anti-Icing Application

Micro and sub-micro-spherical copper powder slurries were elaborately prepared to fabricate different types of porous coating surfaces. These surfaces were further treated with low surface energy modification to obtain the superhydrophobic and slippery capacity. The surface wettability and chemical component were measured. The results showed that both the micro and sub-micro porous coating layer greatly increased the water-repellence capability of the substrate compared with the bare copper plate. Notably, the PFDTES-fluorinated coating surfaces yielded superhydrophobic ability against water under 0 °C with a contact angle of ~150° and a contact angle of hysteresis of ~7°. The contact angle results showed that the water repellency of the coating surface deteriorated with decreasing temperature from 10 °C to -20 °C, and the reason was probably recognized as the vapor condensation in the sub-cooled porous layer. The anti-icing test showed that the ice adhesion strengths of the micro and sub-micro-coated surfaces were 38.5 kPa and 30.2 kPa, producing a 62.8% and 72.7% decrease compared to the bare plate. The PFDTES-fluorinated and slippery liquid-infused porous coating surfaces both produced ultra-low ice adhesion strengths of 11.5-15.7 kPa compared with the other non-treated surfaces, which showed prominent properties for anti-icing and deicing requirement of the metallic surface.

Internal and interfacial microstructure characterization of ice droplets on surfaces by X-ray computed tomography

HYPOTHESIS

Characterizing the microstructure of an ice/surface interface and its effect on the icephobic behavior of surfaces remains a significant challenge. Introducing X-ray Computed Tomography (XCT) can provide unprecedented insights into the internal (porosity) and interfacial structures, i.e. wetting regime, between (super)hydrophobic surfaces and ice by visualizing these optically inaccessible regions.

EXPERIMENTS

Frozen droplets with controlled volume were deposited on top of metallic and polymeric substrates with different levels of wettability. Different modes of XCT (3D and 4D) were utilized to obtain information on the internal and interfacial structure of the ice/surface system. The results were supplemented by conventional surface analysis techniques, including optical profilometry and contact angle measurements.

FINDINGS

Using XCT on ice/surface systems, the 3D and 4D (imaging with temporal resolution) structural information can be visualized. From these datasets, qualitative and quantitative results were obtained, not only for characterizing the interface but also for analyzing the entire droplet/surface system, e.g., measurement of porosity size, shape, and location. These results highlight the potential of XCT in the characterization of both droplets and substrates and proves that the technique can aid to develop hydrophobic surfaces for use as icephobic materials.

Spray-Coated Superhydrophobic Overlayer with Photothermal and Electrothermal Functionalities for All-Weather De/anti-icing Applications

High-performance de/anti-icing overlayers which can be deposited on diverse surfaces offer great potential in many industrial settings and daily life, yet a versatile overlayer applicable to all-weather conditions (high humidity, low temperature, raining, snowing, etc.) is in high demand for practical applications. This study presents the fabrication and application of a superhydrophobic overlayer with a bioinspired hierarchical surface which additionally possesses photothermal and electrothermal functionalities, so it can operate as a de/anti-icing layer in extreme environments. The overlayer, with a papilla-like microstructure similar to that of a lotus leaf, features polydopamine-decorated layered basic zinc acetate microparticles distributed in the framework of multiwalled carbon nanotubes. Specifically, the overlayer is superhydrophobic, and its capability of suppressing the condensation of water droplets and growth of ice crystals is verified by both in situ environmental scanning electron microscopy observations and freezing experiments. Moreover, the overlayer can be warmed up to 74 and 105 °C under the excitation of sunlight and direct current bias, respectively, which is sufficiently high for deicing in severe weather. It is worth mentioning that the overlayer is produced by a spray-coating technique; therefore, it is suitable for large-scale deployment on arbitrary substrate materials. The findings provide insights into a new strategy for engineering multifunctional overlayers and can lead to expanding applications of composite coatings.

Effects of Discontinuous Thermal Conductivity of a Substrate Surface on Ice Adhesion Strength

This study proposes a novel anti-icing model in which silicone rubber with low thermal conductivity is coated at different positions on a material surface to change the continuity of the thermal conductivity of the surface. During the test, the surfaces of aluminum alloy and polymethyl methacrylate (PMMA) are discontinuously coated with silicone rubber. Repeated experiments are conducted to verify the anti-icing effect of the proposed model. Results showed that compared to the conventional surface ice adhesion strength, the rate of reduction of the ice adhesion strength of the aluminum alloy and PMMA could reach 75.07% and 76.70%, respectively, when the novel method is used. Because of the different levels of thermal conductivity at different positions on the material surface, the water attached to the surface locations without the coated silicone rubber had other freezing times. Combined with the heat and phase change of water during the freezing process, changing the stability of the interface between the ice and substrate could act as an active anti-icing power. The ice adhesion strength on the material surface could then be reduced. Compared with the conventional anti-icing methods, the anti-icing method proposed in this study could significantly increase the active anti-icing characteristics of the material and provide a novel anti-icing method for use in engineering applications.

Hybrid Sol-Gel Superhydrophobic Coatings Based on Alkyl Silane-Modified Nanosilica

Hybrid sol-gel superhydrophobic coatings based on alkyl silane-modified nanosilica were synthesized and studied. The hybrid coatings were synthesized using the classic Stöber process for producing hydrophilic silica nanoparticles (NPs) modified by the in-situ addition of long-chain alkyl silanes co-precursors in addition to the common tetraethyl orthosilicate (TEOS). It was demonstrated that the long-chain alkyl substituent silane induced a steric hindrance effect, slowing the alkylsilane self-condensation and allowing for the condensation of the TEOS to produce the silica NPs. Hence, following the formation of the silica NPs the alkylsilane reacted with the silica's hydroxyls to yield hybrid alkyl-modified silica NPs having superhydrophobic (SH) attributes. The resulting SH coatings were characterized by contact angle goniometry, demonstrating a more than 150° water contact angle, a water sliding angle of less than 5°, and a transmittance of more than 90%. Confocal microscopy was used to analyze the micro random surface morphology of the SH surface and to indicate the parameters related to superhydrophobicity. It was found that a SH coating could be obtained when the alkyl length exceeded ten carbons, exhibiting a raspberry-like hierarchical morphology.

Waterborne, non-fluorinated and durable anti-icing superhydrophobic coatings based on diatomaceous earth

Superhydrophobic coatings have great potential for anti-icing compared with conventional techniques (e.g., thermal melting, chemical release and mechanical vibration), but suffer from short water freezing time, environment-unfriendliness, low stability, etc.