Switchable Wettability for Condensation Heat Transfer

Fiber-based photothermal, UV-resistant, and self-cleaning coatings fabricated by silicon grafted copolymers of chitosan derivatives and gallic acid

Superhydrophobic and hydrophobic properties are generally created by adopting low surface free energy materials. Therefore, most studies have focused on creating surface hydrophobicity by using hydrophobic or fluorinated materials. However, few studies are reported on realizing surface hydrophobicity by directly introducing hydrophilic molecules, which is also a challenge. Herein, with platinum nanozyme as the catalyst, the novel hydrophobic coatings have been rapidly gained via anchoring the polymer of hydrophilic gallic acid and chitosan or chitosan quaternary ammonium salt onto cotton fabric surface. Notably, the novel hydrophobic coatings exhibit significant advances compared with conventional hydrophobic ones created by utilizing fluorinated or hydrophobic materials, which breaks the limitation of employing low surface energy materials for gaining surface hydrophobicity. Subsequently, the sodium methyl silicate was grafted on the polymer's coatings to strengthen surface hydrophobicity and the abrasion resistance of hydrophobicity. Interestingly, the heating could induce the hydrophilicity of cotton fabric to recover to hydrophobicity. Moreover, the hydrophobic coatings also possess good photothermal conversion, UV resistance, and anti-oxidation activity for self-cleaning application and oil water separation. Briefly, the present work may open a new direction for preparing novel hydrophobic coatings by combining gallic acid and chitosan-based macromolecular carbohydrates.

Smart surfaces with reversibly switchable wettability: Concepts, synthesis and applications

As a growing hot research topic, manufacturing smart switchable surfaces has attracted much attention in the past a few years. The state-of-the-art study on reversibly switchable wettability of smart surfaces has been presented in this systematic review. External stimuli are brought about to render the alteration in chemical conformation and surface morphology to drive the wettability switch. Here, starting from the fundamental theories related to the surfaces wetting principles, highlights on different triggers for switchable wettability, such as pH, light, ions, temperature, electric field, gas, mechanical force, and multi-stimuli are discussed. Different applications that have various wettability requirement are targeted, including oil-water separation, droplets manipulation, patterning, liquid transport, and so on. This review aims to provide a deep insight into responsive interfacial science and offer guidance for smart surface engineering. It ends with a summary of current challenges, future opportunities, and potential solutions on smart switch of wettability on superwetting surfaces.

A combined structural and wettability gradient surface for directional droplet transport and efficient fog collection

HYPOTHESIS

The droplet manipulation behavior is affected by chemical structural driving force (including the superposition of electric, magnetic, optical and thermal fields), which directly determine transportation velocity. A lot of research has focused on a single driving force that induces the directional transportation behavior, which affects its performance.

EXPERIMENTS

A simple method for preparing wettability gradient conical copper needles (WGCCN) combining structural gradient and chemical gradient was formulated. The effect of droplet volume and tilt angles on droplet transport velocity was systematically studied. The process of droplet transport was revealed through theoretical model and mechanical analysis. Finally, the application of WGCCN and its array model in fog collection were explored.

FINDINGS

A continuous chemical gradient in the conical structure gradient induces the droplet directional transportation, and the transportation velocity depends on the droplet volume. In addition, under the cooperation effect of multiple driving force, the droplet can still be transported in a directional orientation even if it is tilted at a certain angle. The simple droplet manipulation behavior portends that the droplets directional transport behavior can be applied in microfluidic manipulation by cooperation of effective multiple driving force with satisfactory results.

Smart Bionic Surfaces with Switchable Wettability and Applications

In order to satisfy the needs of different applications and more complex intelligent devices, smart control of surface wettability will be necessary and desirable, which gradually become a hot spot and focus in the field of interface wetting. Herein, we review interfacial wetting states related to switchable wettability on superwettable materials, including several classical wetting models and liquid adhesive behaviors based on the surface of natural creatures with special wettability. This review mainly focuses on the recent developments of the smart surfaces with switchable wettability and the corresponding regulatory mechanisms under external stimuli, which is mainly governed by the transformation of surface chemical composition and geometrical structures. Among that, various external stimuli such as physical stimulation (temperature, light, electric, magnetic, mechanical stress), chemical stimulation (pH, ion, solvent) and dual or multi-triggered stimulation have been sought out to realize the regulation of surface wettability. Moreover, we also summarize the applications of smart surfaces in different fields, such as oil/water separation, programmable transportation, anti-biofouling, detection and delivery, smart soft robotic etc. Furthermore, current limitations and future perspective in the development of smart wetting surfaces are also given. This review aims to offer deep insights into the recent developments and responsive mechanisms in smart biomimetic surfaces with switchable wettability under external various stimuli, so as to provide a guidance for the design of smart surfaces and expand the scope of both fundamental research and practical applications.

Biomimetic fog collection and its influencing factors

This review starts with the main process of fog collection and then analyzes the influencing factors that affect the efficiency of fog collection.