Hongjun Kang

Self-Restoration of Superhydrophobicity on Shape Memory Polymer Arrays with Both Crushed Microstructure and Damaged Surface Chemistry.

Recently, self-healing superhydrophobic surfaces have become a new research focus due to their recoverable wetting performances and wide applications. However, until now, on almost all reported surfaces, only one factor (surface chemistry or microstructure) can be restored. In this paper, a new superhydrophobic surface with self-healing ability in both crushed microstructure and damaged surface chemistry is prepared by creating lotus-leaves-like microstructure on the epoxy shape memory polymer (SMP). Through a simple heating process, the crushed surface microstructure, the damaged surface chemistry, and the surface superhydrophobicity that are destroyed under the external pressure and/or O2 plasma action can be recovered, demonstrating that the obtained superhydrophobic surface has a good self-healing ability in both of the two factors that govern the surface wettability. The special self-healing ability is ascribed to the good shape memory effect of the polymer and the reorganization effect of surface molecules. This paper reports the first use of SMP material to demonstrate the self-healing ability of surface superhydrophobicity, which opens up some new perspectives in designing self-healing superhydrophobic surfaces. Given the properties of this surface, it could be used in many applications, such as self-cleaning coatings, microfluidic devices, and biodetection.

Under-Oil Switchable Superhydrophobicity to Superhydrophilicity Transition on TiO2 Nanotube Arrays

Recently, smart interfacial materials that can reversibly transit between the superhydrophobicity and superhydrophilicity have aroused much attention. However, all present performances happen in air, and to realize such a smart transition in complex environments, such as oil, is still a challenge. Herein, TiO2 nanotube arrays with switchable transition between the superhydrophobicity and superhydrophilicity in oil are reported. The switching can be observed by alternation of UV irradiation and heating process, and the smart controllability can be ascribed to the cooperative effect between the surface nanostructures and the chemical composition variation. By using the controllable wetting performances, some applications such as under-oil droplet-based microreaction and water-removal from oil were demonstrated on our surface. This paper reports a surface with smart water wettability in oil, which could start some fresh ideas for wetting control on interfacial materials.

Frictional Reduction with Partially Exfoliated Multi-Walled Carbon Nanotubes as Water-Based Lubricant Additives

In this work, partially exfoliated multi-walled carbon nanotubes (Px-CNTs) were prepared by oxidizing multi-walled carbon nanotubes (MWCNTs) and applied into water-based lubricant as a kind of new additives, resulting in an outstanding anti-friction effect. The Px-CNTs have the structures of both MWCNTs and graphene oxide nanoribbons (GONRs). The special structure could prevent aggregation in water-based lubricant and reduce friction effectively. At the same time, Px-CNTs generate both sliding and rolling friction like MWCNTs and GONRs simultaneously. The friction force of Px-CNTs tended to go up after declining with increasing its loading, suggesting the existence of optimum additive amount of additions. Compared with water, water with 0.5 wt% Px-CNTs further reduced the friction force up to 66.4%. Compared with CNTs-COOH and GONRs dispersed in water via a similar method, Px-CNTs in water displays remarkable friction characteristic, suggesting that the friction force of water with 0.5 wt% Px-CNTs is decreased by 19.82% and 13.82% compared with water with 0.3 wt% MWCNTs and GONRs.

Modified MXene/Holey Graphene Films for Advanced Supercapacitor Electrodes with Superior Energy Storage

Abstract MXene films are attractive for advanced supercapacitor electrodes requiring high volumetric energy density due to their high redox capacitance combined with extremely high packing density. However, the self‐restacking of MXene flakes unavoidably decreases the volumetric performance, mass loading, and rate capability. Herein, a simple strategy is developed to prepare a flexible and free‐standing modified MXene/holey graphene film by filtration of the alkalized MXene and holey graphene oxide dispersions, followed by a mild annealing treatment. After terminal groups (—F/—OH) are removed, the increased proportion of Ti atoms enables more pseudocapacitive reaction. Meanwhile, the embedded holey graphene effectively prevents the self‐restacking of MXene and forms a high nanopore connectivity network, which is able to immensely accelerate the ion transport and shorten transport pathways for both ion and electron. When applied as electrode materials for supercapacitors, it can deliver an ultrahigh volumetric capacitance (1445 F cm−3) at 2 mV s−1, excellent rate capability, and high mass loading. In addition, the assembled symmetric supercapacitor demonstrates a fantastic volumetric energy density (38.6 Wh L−1), which is the highest value reported for MXene‐based electrodes in aqueous electrolytes. This work opens a new avenue for the further exploration of MXene materials in energy storage devices.