Role of Water Solidification Concepts in Designing Nano-Textured Anti-Icing Surfaces

Environment-friendly bio-based controlled-release phosphate fertilizer with waste kitchen oil as coating material: Preparation, characterization, and mechanisms

Recently, Bio-based polyurethane controlled-release fertilizers (BPCF) have been developed rapidly owing to their environmental friendliness, renewability, and low cost. However, the unsatisfying controlled release prohibits their large-scale direct application in agricultural production. Here, we prepared bio-based controlled-release phosphate (P) fertilizers using harmful waste kitchen oils (WKO) as coating materials. The membrane shell surface was modified with multi-walled carbon nanotubes (CNT), and superhydrophobic controlled-release phosphorus fertilizers (SCRF) were obtained. After CNT modification, the controlled release period of SCRF was greatly improved. Phosphorus released period of SCRF reached over 67 d while that of BPCF was merely ∼49 d. Additionally, the surface energy, cracks, roughness, microstructure, cross-linking degree, etc., of the membrane shells were measured. The results showed that CNT greatly improved the hydrophobic properties of the membrane shells. The findings indicated the application of modified WKO with great agricultural value in preparing environment-friendly BPCFs.

Icephobic/anti-icing properties of superhydrophobic surfaces

In the winter, icing on solid surfaces is a typical occurrence that may create a slew of hassles and even tragedies. Anti-icing surfaces are one of the effective solutions for this kind of problem. The roughness of a superhydrophobic surface traps air and weakens the contact between the solid surface and liquid water, allowing water droplets to be removed before freezing. At present, the conventional anti-icing methods including mechanical or thermal technology are not only surface structure unfriendly but also have the obsessions of low efficiency, high energy consumption and high manufacturing costs. Hence, developing a way to remove ice by just modifying the surface shape or chemical composition with a low surface energy is extremely desirable. Numerous attempts have been made to investigate the evolution of ice nucleation and icing on superhydrophobic surfaces under the direction of the ice nucleation hypothesis. In this paper, the research progress of ice nucleation in recent years is reviewed from theoretical and application. The icephobic surfaces are described using the wettability and classical nucleation theories. The benefits and drawbacks of anti-icing superhydrophobic surface are summarized, as well as deicing methods. Finally, several applications of ice phobic materials are illustrated, and some problems and challenges in the research field are discussed. We believed that this review will be useful in guiding future water freezing initiatives.

Superhydrophobic materials used for anti-icing Theory, application, and development

The accumulation of ice will reduce the performance of the base material and lead to all kinds of damage, even a threat to people's life safety. Recent increasing studies suggest that superhydrophobic surfaces (SHSs) originating from nature can remove impacting and condensing droplets from the surface before freezing to subzero temperatures, and it can be seen that hydrophobic/SH coating has good freezing cold resistance. But such anti-icing performances and developments in practical applications are restricted by various factors. In this paper, the mechanism and process of surface icing phenomenon are introduced, as well as how to prevent surface icing on SHS. The development of SH materials in the aspect of anti-icing in recent years is described, and the existing problems in the aspect of anti-icing are analyzed, hoping to provide new research ideas and methods for the research of anti-icing materials.

Anti-Icing Properties of Vertically Aligned TiO2 Nanopillars

Inspired by the superhydrophobic and anti-icing properties of Berberis thunbergii leaves for the first time, a surface with vertically aligned TiO₂ nanopillars (VATiO₂NPIs) has been developed, which shows excellent anti-icing properties even at -25 °C. The height and diameter of TiO₂NPIs arrays were 200 and 70 nm, respectively, and were fabricated using TiO₂ atomic-layer deposition in an aqueous solution on an anodized aluminum oxide substrate and modified with stearic acid. The water contact angle measurements for VATiO₂NPI-based aluminum surfaces indicated high contact angle (170.2°), low contact angle hysteresis (5°), excellent delay time (385 s), appropriate robustness (>20 cycles of freeze-melt), and low adhesion strength (<95 kPa). The VATiO₂NPI surface analyses were done using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectroscopy (XRD), and Fourier transform infrared spectroscopy (FT-IR) methods, and they showed that the stearic acid stably absorbed on VATiO₂NPIs. Our results indicated that the long delay time of the heterogeneous nucleation and freezing process could be obtained by the desired structural match between the VATiO₂NPI apices and water molecules in the initiation of the heterogeneous nucleation. In this study, smooth apices of the VATiO₂NPIs with highly potent morphology presented significant anti-icing properties because of the strong phonon scattering between nanopillars that can interrupt the heat transfer process. Such results are not achievable by conventional anti-icing methods and give new insight into the mechanism of the anti-icing process.

Transparent Electrothermal Film Defoggers and Antiicing Coatings based on Wrinkled Graphene

Fog, frost, ice, and other natural phenomena can inevitably affect human life and the function of equipment. Therefore, removal or prevention is an urgent problem to be solved. As a new type of 2D material, graphene possesses great application potential in defogging and antiicing. In this work, a graphene film with intentionally increased defects and uniformly distributed wrinkles is synthesized on copper-zinc alloy substrates by chemical vapor deposition, and transparent electrothermal film defoggers are prepared based on such material. The defoggers can completely remove fog within 5 s when supplying a safe voltage of 28 V. The surface resistance of the defoggers is sensitive to humidity and it can monitor the defogging process in real time. Such outstanding performance is attributed to the ultrafast evaporation mechanism, which can prevent excessive water accumulation. The antiicing performance of wrinkled graphene (WG) is further studied. The antiicing coatings can delay freezing for 1.25 h at -15 °C or 2.8 h at -10 °C. The superior performance of WG can be explained by its unique surface structure and nanoscale roughness. Taken together, WG is expected to be used in antifog glass, rearview mirror defogging, aircraft surface deicing, and other applications.

Icephobic Strategies and Materials with Superwettability: Design Principles and Mechanism

Ice formation and accretion on surfaces is a serious economic issue in energy supply and transportation. Recent strategies for developing icephobic surfaces are intimately associated with superwettability. Commonly, the superwettability of icephobic materials depends on their surface roughness and chemical composition. This article critically categorizes the possible strategies to mitigate icing problems from daily life. The wettability and classical nucleation theories are used to characterize the icephobic surfaces. Thermodynamically, the advantages/disadvantages of superhydrophobic surfaces are discussed to explain icephobic behavior. The importance of elasticity, slippery liquid-infused porous surfaces (SLIPSs), amphiphilicity, antifreezing protein, organogels, and stimuli-responsive materials has been highlighted to induce icephobic performance. In addition, the design principles and mechanism to fabricate icephobic surfaces with superwettability are explored and summarized.

Frosting Performance of a Nanoporous Hydrophilic Aluminum Surface

As an efficient energy-saving piece of equipment, an air-source heat pump can not only reduce the energy consumption required for heating, but can also reduce the pollution from fossil consumption. However, when an air-source heat pump operates under low temperatures and high humidity, the heat exchanger surface of its outdoor evaporator often get covered with frost. The growth of the frost layer seriously affects the operation efficiency of the equipment and limits its engineering application. Looking for materials that can actively inhibit frost forming is a good strategy to solve the problem mentioned above. Numerous studies show that a hydrophilic surface (contact angle less than 90°) can inhibit the normal freezing process. Manufacturing nanostructures on the surface also affect frosting performance. In this paper, nanoporous hydrophilic aluminum sheets, with contact angles of 47.8° (Sample 2), 35.9° (Sample 3), and 22.9° (Sample 4), respectively, were fabricated by the anodic oxidation method. The frosting performance of the nanoporous hydrophilic aluminum was studied compared with polished aluminum, with a contact angle of 60.2° (Sample 1). The frosting performance of the aluminum surface was systematically studied by observing the frost structure from top and side cameras and measuring the frost thickness, frost mass, and frosting rate. It was found that nanoporous hydrophilic aluminum can reduce the frost thickness and frost mass. The frost mass reduction rate of sample 2 reached a maximum of 65.9% at the surface temperature of −15 °C, under test conditions. When the surface temperature was −15 °C, the frosting rate of Sample 2 was 1.71 g/(m2·min), which was about one-third of that on sample 1 (polished aluminum). Nanoporous hydrophilic aluminum behaved better at lessening frost than polished aluminum, which revealed that manufacturing nanopores and promoting hydrophilicity can delay the formation of frost.

Smart, Piezo-Responsive Polyvinylidenefluoride/Polymethylmethacrylate Surface with Triggerable Water/Oil Wettability and Adhesion

The design of smart surfaces with externally triggerable water/oil wettability and adhesion represents one of the most up-to-date challenges in the field of material science. In this work, the intelligent surface with electrically triggerable wettability and water/oil adhesion is presented. As a basic material background exhibiting electric field (EF) sensitivity, the piezo-responsive polymethylmethacrylate/polyvinylidenefluoride polymer fibers were used. To expand the available range of water/oil contact angles (CAs) and adhesion, the fibers were grafted with hydrophilic or hydrophobic functional groups using diazonium chemistry. The fiber functionality was evaluated using the static CA and wettability hysteresis measurements (increasing/decreasing drop volume and tilting angles), drops adhesion/repellence and graphite self-cleaning test performed with and without the application of EF. It was found that the proposed method enables tuning the surface wettability in the superhydrophobic/superoleophobic-hydrophilic/oleophilic range and changing of surface properties from low adhesive to high adhesive for water and oil. More convincing results were achieved in the case of fiber surface modification by ADT-C₈F₁₇, which may result from a rearrangement of the grated -C₆H₄C₈F₁₇ functional group under the application of EF triggering. Moreover, the triggering which can be performed in the extremely fast way (the surface responds to the EF switching on/off in seconds) was found to be fully reversible. Finally, the additional tests indicate the satisfactory stability of created fiber-based coating against the mechanical treatment.