Nanocellulose‐based strain sensor (NBSS) have been a subject of growing interest for wearable electronics. However, these electronic devices are susceptible to damage when they come into contact with water and organic contaminants. Recently, researchers have developed a superhydrophobic NBSS. Unfortunately, it does not treat organic pollutants in water when used in an underwater environment. In this paper, a new solution: a superhydrophobic photocatalytic self‐cleaning NBSS created through scrape coating and dip coating methods is proposed. This new method shows outstanding self‐cleaning capabilities against water and organic contaminants due to the synergistic effects of the superhydrophobicity and photocatalysis of MnO₂ nanoparticles. Furthermore, the superhydrophobic photocatalytic self‐cleaning NBSS has an exceptional response time of 0.66 s, a fast recovery time of 0.81 s, a sensitivity ≈66.53 at a strain of 0.5%. It is expect that the superhydrophobic photocatalytic self‐cleaning NBSS can monitor human movements, including finger twists, wrist movements, elbow bends, and knee movements. Not only is the fabrication method cost‐effective and scalable, but the new NBSS holds great promise in a wide range of fields, including human‐machine interactive systems, smart systems, and human‐body monitoring. Overall, the study provides significant guidance for future designs for wearable strain sensors.

Superhydrophobic surfaces offer notable advantages, including markedly low water affinity and reduced ice adhesion strength. Nevertheless, their practical utility is impeded by their limited durability and vulnerability to failure in cold and humid environments. In this study, a novel approach for devising an electro‐photothermal superhydrophobic (EPS) nanocomposite coating is presented. The findings indicate that the EPS nanocomposite coating exhibits both physical and chemical self‐cleaning attributes, showcasing a synergistic interplay of superhydrophobicity, electrothermal, and photothermal characteristics. The superhydrophobic coating delays icing about four times longer than the original coating. At ambient temperatures of −20 °C, the coating stacked with an electro‐ and photo‐thermal performance de‐icing layer reduces the de‐icing time by about 5 times more than the purely photo‐thermal performance de‐icing time, and reduces the de‐icing time by about 4 times more than the purely electro‐thermal de‐icing time. Furthermore, the EPS surface demonstrates the capability to sustain temperatures above 0 °C through the photothermal effect on sunny days, utilizing both the electrothermal and photothermal effects on cloudy days, and relying on the electrothermal effect during cold nights. The research introduces a novel method for fabricating functional materials, pertinent to practical anti‐icing and de‐icing applications.

A liquid–gas interface (LGI) on submerged microstructure surfaces has the potential to achieve large slip velocities, which is significant for underwater applications such as drag reduction. However, surfactants adsorbing on the LGI can cause surface tension gradient against the mainstream, which weakens the flow near the LGI and severely limits drag reduction. The mechanism of the effect of surfactants on two-dimensional flows has already been proposed, while the effect of surfactants on the three-dimensional flow near the LGI is still not clear. In our study, we specifically design an experimental system to directly observe a three-dimensional backflow at the LGI. The formation as well as the behaviour of the backflow are demonstrated to be significantly influenced by the surfactant. Combining experimental measurements, theoretical analyses and numerical simulations, we reveal the underlying mechanism of the backflow, which is a competition between the mainstream and the Marangoni flows generated by the interfacial concentration gradients of surfactant simultaneously in streamwise and spanwise directions, reflecting the three-dimensional feature of the backflow. In addition, a kinematic similarity is obtained to characterize the backflow. The current work provides a model system for investigating the three-dimensional backflow at the LGI with surfactants, which is significant for practical applications such as drag reduction and superhydrophobicity.

Taylor-Couette flow with micro-grooves on the rotating inner cylinder is investigated to reveal the effect of surface structures on drag reduction. The Reynolds number (Re) ranges from 160 to 18700. On the one hand, in the regimes of wave vortex flow (WVF, 160＜Re＜1010) and modulated wavy vortices (MWV, 1010＜Re＜1380) flow, the micro-grooves always reduce the torque, indicating drag reduction. Increasing either the size of micro-groove or Re, drag reduction will be enhanced. On the other hand, when the flow regime enters into turbulent Taylor vortices (TTV, Re＞1380), drag reduction will be suppressed as Re increases, and eventually turns to drag increase. The bigger the groove size, the smaller the critical Re where it turns from drag reduction to drag increase. To reveal the underlying mechanisam of the effect of micro-grooves on drag reduction, particle image velocimetry (PIV) measurements are conducted to observe the vortex flow structures, which demonstrates two aspects affecting the drag of Taylor-Couette flow over micro-grooved wall. First, the weakening of the large-scale Taylor vortex will lead to drag reduction. Second, the roughness effect will result in drag increase. In WVF/MWV, the former plays a dominant role, while in TTV, the latter dominates. In addition, a relationship between the micro-groove size and the predictive critical Reynolds number (Re_c) is developed, providing a method for controlling the wall drag.