A Superhydrophobic Smart Coating for Flexible and Wearable Sensing Electronics

Superhydrophobic surfaces have shown versatile applications in waterproofing, self‐cleaning, drag reduction, selective absorption, etc. The most convenient and universally applicable approach to forming superhydrophobic surfaces is by coating; however, currently, superhydrophobic, smart coatings with flexibility and multiple functions for wearable sensing electronics are not yet reported. Here, a highly flexible multifunctional smart coating is fabricated by spray‐coating multiwalled carbon nanotubes dispersed in a thermoplastic elastomer solution, followed by treatment with ethanol. The coatings not only endow various substrate materials with superhydrophobic surfaces, but can also respond to stretching, bending, and torsion—a property useful for flexible sensor applications. The coatings show superior sensitivity (gauge factor of 5.4–80), high resolution (1° of bending), a fast response time (<8 ms), a stable response over 5000 stretching–relaxing cycles, and wide sensing ranges (stretching: over 76%, bending: 0°–140°, torsion: 0–350 rad m^?1). Moreover, multifunctional coatings with thicknesses of only 1 µm can be directly applied to clothing for full‐range and real‐time detection of human motions, which also show extreme repellency to water, acid, and alkali, which helps the sensors to work under wet and corrosive conditions.     

Bioinspired Mechanically Robust Metal‐Based Water Repellent Surface Enabled by Scalable Construction of a Flexible Coral‐Reef‐Like Architecture

Mechanical robustness is a central concern for moving artificial superhydrophobic surfaces to application practices. It is believed that bulk hydrophilic materials cannot be use to construct micro/nanoarchitectures for superhydrophobicity since abrasion‐induced exposure of hydrophilic surfaces leads to remarkable degradation of water repellency. To address this challenge, the robust mechanical durability of a superhydrophobic surface with metal (hydrophilic) textures, through scalable construction of a flexible coral‐reef‐like hierarchical architecture on various substrates including metals, glasses, and ceramics, is demonstrated. Discontinuous coral‐reef‐like Cu architecture is built by solid‐state spraying commercial electrolytic Cu particles (15–65 µm) at supersonic particle velocities. Subsequent flame oxidation is applied to introduce a porous hard surface oxide layer. Owing to the unique combination of the flexible coral‐reef‐like architecture and self‐similar manner of the fluorinated hard oxide surface layer, the coating surface retains its water repellency with an extremely low roll‐off angle (<2°) after cyclic sand‐paper abrasion, mechanical bending, sand‐grit erosion, knife‐scratching, and heavy loading of simulated acid rain droplets. Strong adhesion to glass, ceramics, and metals up to 34 MPa can be achieved without using adhesive. The results show that the present superhydrophobic coating can have wide outdoor applications for self‐cleaning and corrosion protection of metal parts.     

耐久可拉伸超疏水材料的构建及应用研究进展EI北大核心

可拉伸超疏水材料能大幅度提升疏水材料的力学性能,在未来科技产品中应用潜力极大。可拉伸超疏水材料制备方法分为弹性材料的使用、可拉伸结构的设计、弹性材料与可拉伸结构的结合。本文分析了各类制备方法的原理及优缺点,总结了提高可拉伸超疏水材料耐久性的有效措施,阐述了可拉伸超疏水材料在柔性传感器、新兴电子设备、医疗防护、液相混合物纯化、微液滴控制领域的应用原理及特点。现有可拉伸超疏水材料尚面临耐久性能不足、制备成本高、工艺复杂等问题,研究应聚焦于材料体系的进一步开发、拉伸原理的完善以及新技术新工艺的引入。未来的发展方向是轻薄、柔性、绿色环保、智能化和精细化。     

Robust Flower‐Like TiO2@Cotton Fabrics with Special Wettability for Effective Self‐Cleaning and Versatile Oil/Water Separation

Inspired by the hierarchical structure of the mastoid on the micrometer and nanometer scale and the waxy crystals of the mastoid on natural lotus surfaces, a facile one‐step hydrothermal strategy is developed to coat flower‐like hierarchical TiO₂ micro/nanoparticles onto cotton fabric substrates (TiO₂@Cotton). Furthermore, robust superhydrophobic TiO₂@Cotton surfaces are constructed by the combination of hierarchical structure creation and low surface energy material modification, which allows versatility for self‐cleaning, laundering durability, and oil/water separation. Compared with hydrophobic cotton fabric, the TiO₂@Cotton exhibits a superior antiwetting and self‐cleaning property with a contact angle (CA) lager than 160° and a sliding angle lower than 5°. The superhydrophobic TiO₂@Cotton shows excellent laundering durability against mechanical abrasion without an apparent reduction of the water contact angle. Moreover, the micro/nanoscale hierarchical structured cotton fabrics with special wettability are demonstrated to selectively collect oil from oil/water mixtures efficiently under various conditions (e.g., floating oil layer or underwater oil droplet or even oil/water mixtures). In addition, it is expected that this facile strategy can be widely used to construct multifunctional fabrics with excellent self‐cleaning, laundering durability, and oil/water separation. The work would also be helpful to design and develop new underwater superoleophobic/superoleophilic materials and microfluidic management devices.     

碳纤维颗粒增强CeO2/PMMA/PVDF超疏水复合涂层及其耐磨性能

提高耐磨性能是推动仿生超疏水表面走向实际应用的关键挑战之一。设计了二氧化铈微米粒子增强PMMA/PVDF超疏水复合涂层配方,获得了水珠接触角达152°、水珠滚动角为5°的超疏水复合涂层。该涂层经过落砂磨损试验后接触角下降为103°、滚动角增大为20°。采用碳纤维颗粒对CeO2/PMMA/PVDF超疏水复合涂层进行增强,优化配方的接触角达153°、滚动角达到5°。经过相同落砂磨损试验后,增强后的复合涂层水珠接触角能在一定程度磨损后达到140°左右。可见,CeO2/PMMA/PVDF复合涂层具有良好的超疏水性能,碳纤维颗粒增强是提高该涂层耐磨性能的有效方法。     

Fabrication of superhydrophobic and oleophobic zinc coating on steel surface

In this work, a simple method, including electrodeposition and chemical modification, for fabrication of a superhydrophobic and oleophobic coating on steel substrate is reported. The surface morphology of this coating showed concave structure, and the contact angles of water and glycerol on this coating surface were about 153.57° and 149.32°, respectively. In addition, the water droplet was easy to roll on this coating surface, and the sliding angle was smaller than 10°. The contact angle of the water/ethanol droplet with different surface tension, from 56 to 36?mN?m^?1, was also >130° on this coating surface, indicating this as superhydrophobic and oleophobic coating surface with good lyophobicity. Moreover, this coating surface had excellent non-sticking property for the water droplet under a certain external pressure, self-cleaning property and long-term stability.     

普鲁士蓝/氟化超支化聚氨酯复合涂层材料及其光热转换超疏水性能

首先制备氟化超支化聚氨酯(FHPU),然后与具有光热转化功能的普鲁士蓝(PB)纳米粒子复合,得到光热转换功能的PB/FHPU超疏水防结冰复合涂层材料。利用FTIR、TGA和DSC等测试分析了FHPU和PB/FHPU超疏水防结冰复合涂层材料的结构及性能,通过光热转换实验证明了复合涂层材料出色的光热性能;深入探究了PB纳米粒子的添加量对复合涂层材料表面性质和光热转化性能的影响。结果表明,当PB质量占FHPU的13%时,复合涂层材料可形成具有微纳结构的复合涂层,涂层表面最大接触角达157°,滚动角为1.8°。同时,该涂层在808 nm激光照射下10 s内温度可升高78.1℃,最高温度达到148.7℃。因而,光热转换功能性超疏水防结冰复合涂层材料具有良好的疏水、防结冰性能。      

Wettability control of ZnO nanoparticles for universal applications

Herein, a facile approach for the fabrication of a superhydrophobic nanocoating through a simple spin-coating and chemical modification is demonstrated. The resulting coated surface displayed a static water contact angle of 158° and contact angle hysteresis of 1°, showing excellent superhydrophobicity. The surface wettability could be modulated by the number of ZnO nanoparticle coating cycles, which in turn affected surface roughness. Because of its surface-independent characteristics, this method could be applicable to a wide range of substrates including metals, semiconductors, papers, cotton fabrics, and even flexible polymer substrates. This superhydrophobic surface showed high stability in thermal and dynamic conditions, which are essential elements for practical applications. Furthermore, the reversible switching of wetting behaviors from the superhydrophilic state to the superhydrophobic state was demonstrated using repeated chemical modification/heat treatment cycles of the coating films.     

Stretchable Transparent Conductors: from Micro/Macromechanics to Applications

Stretchable transparent conductors (STCs), generally consisting of conducting networks and stretchable transparent elastomers, can maintain stable conductivity and transparency even at large tensile strain, beyond the reach of rigid/flexible transparent conductors. They are essential components in stretchable/wearable electronics for using on irregular 3D conformable surfaces and have attracted tremendous attention in recent years. This review aims to provide systematical correlation of the conducting element–substrate interaction with the structural stability of conducting networks, as well as the properties and device applications of STCs. It starts with the micromechanics for stretching of conducting elements on substrates, including the mechanical mismatch, distribution/level of interfacial shear stress, and the deformation behavior of conducting elements on substrates. The macromechanics for stretching of conducting networks on substrates are then further illustrated from a more statistical point of view, namely sliding/preferred orientation of percolation networks, unfolding of buckled structures, and unit cell distortion/distributed rupture of nanomeshes. The structure‐dependent properties as well as the state‐of‐the‐art applications of STCs are summarized before ending with the conclusions and outlooks for STCs.     

Stable superhydrophobic surface: fabrication of interstitial cottonlike structure of copper nanocrystals by magnetron sputtering

Abstract

A stable superhydrophobic copper surface was obtained by radio-frequency magnetic sputtering on Si (100) and quartz substrates. The water contact angle and sliding angle of the superhydrophobic copper surface were 160.5° and 3±1.9°, respectively. Scanning electron microscopy (SEM) photos show that the superhydrophobic surface structure comprises many uniform nanocrystals with a diameter of about 100 nm. A brief explanation of the formation of this special microstructure and the mechanism of its wettability were proposed.     

Highly transparent, flexible, and thermally stable superhydrophobic ORMOSIL aerogel thin films

We report preparation of highly transparent, flexible, and thermally stable superhydrophobic organically modified silica (ORMOSIL) aerogel thin films from colloidal dispersions at ambient conditions. The prepared dispersions are suitable for large area processing with ease of coating and being directly applicable without requiring any pre- or post-treatment on a variety of surfaces including glass, wood, and plastics. ORMOSIL films exhibit and retain superhydrophobic behavior up to 500 °C and even on bent flexible substrates. The surface of the films can be converted from superhydrophobic (contact angle of 179.9°) to superhydrophilic (contact angle of <5°) by calcination at high temperatures. The wettability of the coatings can be changed by tuning the calcination temperature and duration. The prepared films also exhibit low refractive index and high porosity making them suitable as multifunctional coatings for many application fields including solar cells, flexible electronics, and lab on papers.     

Pulsed Laser Modulated Shock Transition from Liquid Metal Nanoparticles to Mechanically and Thermally Robust Solid–Liquid Patterns

In this work, a general mechanism is discovered to form liquid‐metal‐based, stable and stretchable conductive patterns on rigid and soft substrates. It is discovered that pulsed laser irradiation of liquid metal nanoparticles (LMNPs) with tunable conditions can induce transformation to stable and stretchable solid–liquid (S–L) dual phases on various surfaces. Formation of this unique solid–liquid composite phase is the key to change the wetting behavior of the conductive patterns on various substrates and enables mechanically stable patterns on various substrates. Pulsed‐laser‐driven thermo‐mechanical shock momentum is important for rupture and joining of the LMNPs, providing much better control than the traditional mechanical sintering. The solid nanophase forms a nanoporous matrix filled with and wetted by the LM, thereby providing a stabilization mechanism for the S–L composite patterned thin film. The mechanical and thermal reliability of the solid–liquid patterns is investigated. The S–L patterns can stretch up to 30% strain and cycle stably for 7000 cycles. It can be heated up to 177 °C with an input power of 0.58 W. The solid–liquid composite film provides great opportunity for various applications as a flexible conductor with unique mechanical and physics properties and further inspires design of LM devices for completely exposed applications.     

Superhydrophobic Coatings for Technical Applications

Water repellent coatings developed in this work showed that two superimposed rough structures are required to generate superhydrophoby with WCA >150°. A micro rough surface overcoated with a submicro or nano rough hydrophobic material behave similar to the hierarchical structures found on leafs of some plants which generate the highly mobile Cassie/Baxter droplets. Coatings of inorganic and organic materials were performed by thermal spraying (inorganic materials) and spraycoating (organic materials) on sandblasted metal, mainly stainless steel, surfaces. Hierarchical roughness structures were developed by thermal treatment of pure and composite fluoropolymeric layers. Such hierarchical superhydrophobic coating systems showed water contact angles between 160° and 170°. The coatings have good mechanical stability and can be applied in numerous technical applications.     

Nanoimprinting of Flexible Polycarbonate Sheets with a Flexible Polymer Mold and Application to Superhydrophobic Surfaces

This study demonstrates a reliable process for the direct nanoimprinting of a flexible polycarbonate (PC) sheet using a perfluoropolyether (PFPE) mold. PC is a commonly used flexible substrate with optical transparency, low thermal expansion coefficient, high mechanical strength, and excellent deformation resistivity. The imprint performances of PFPE, hard/soft‐polydimethylsiloxane, and silicon molds are compared. Given that the heating temperature is near the glass transition temperature (≈153 °C) of PC, only PFPE mold can be fully patterned into PC substrate with viable integrity. The mechanical property and gas permeability of the materials are investigated to determine the mechanism of the flexible PFPE mold, which performs better than a rigid silicon mold. Nanoimprint process using a PFPE mold is performed at 153 °C and 5 bars. The lower imprint temperature or imprint pressure of the proposed process compared with those from previous studies is favorable in nanoimprinting. Finally, nanoroughness‐on‐nanopillar hierarchical surfaces, which possess superhydrophobic slippery characteristics superior to those of nanoroughness‐only surfaces, are obtained by treating PC nanopillar arrays imprinted by PFPE mold with C₄F₈ plasma.     

阳极氧化法制备铝基超疏水涂层及其稳定性和耐蚀性的研究

铝由于在潮湿的环境中很容易受到污染和损坏,从而严重影响了其美观性和用途。为了改善铝基材料的耐腐蚀性能,采用电化学阳极氧化法与十四酸修饰相结合的方式在铝基底上制备了超疏水涂层。通过场发射扫描电镜(FESEM)和X射线能量色散光谱(EDS)对涂层表面形貌和化学组成进行了表征。同时利用接触角测量仪、喷砂实验和电化学测试分别对涂层表面的润湿性、机械稳定性以及耐腐蚀性能进行了研究。结果表明:当阳极氧化电压为20V时,所制备的涂层为最佳铝基超疏水涂层,此时涂层的接触角为(155.2±0.5)°,滚动角为(3.5±1.3)°。其对应的腐蚀电流密度较铝基底降低了2个数量级,腐蚀电位从-0.629V正移到-0.570V,呈现出优异的耐腐蚀性能。此外,该涂层还具有良好的机械稳定性。     

超疏水SiO2/PS 薄膜于木材表面的构建

通过溶胶-凝胶法一步合成疏水性且具备独特形貌的二氧化硅粒子,联合聚苯乙烯以滴涂的方式于木材表面仿生合成了稳定性超疏水薄膜。经处理后的木材表面与水的静态接触角为153°,滚动角小于5°。通过扫描电子显微镜照片观察到该复合涂层拥有微米/亚微米的二维等级粗糙结构,该结构协同低表面能物质共同决定超疏水性木材的成功制得。此外,进一步研究了超疏水性木材表面的稳定性和耐久性。结果表明,该超疏水性木材于水、腐蚀性液体(酸液/碱液)、常见有机溶剂中以及一些常见条件下仍保留超疏水特性,为未来木材材料的应用领域扩展提供了有利条件。     

纳米SiO2@超支化PDMS复合超疏水涂层的制备与性能调控

超疏水涂层在实际应用中受化学腐蚀、刮擦磨损等外界环境的影响,易造成涂层老化、开裂甚至脱落,造成涂层失效。因此,针对这一问题,设计出具备耐候性的自修复超疏水表面：以超支化聚二甲基硅氧烷为柔性基底和低表面能物质,引入纳米二氧化硅构筑表面粗糙结构,制备超疏水涂层。当SiO₂粒径为50 nm、固含量为30wt%时,得到了接触角为154.87°的超疏水涂层。经过5次胶带剥离试验,涂层表现出良好的机械稳定性。经历10次温差循环试验和24 h紫外光照射后,涂层表面接触角仍大于150°,表明涂层具有良好的耐候性。涂层经过80℃、2 h的热处理可修复划痕,表明该涂层具有一定的自修复功能。同时,Tafel及Nyquist测试结果表明,对基底进行超疏水处理可显著提高防腐性能,并且该涂层具有明显的自清洁效果。综上所述,本文所制备的纳米SiO₂@超支化聚二甲基硅氧烷(PDMS)复合超疏水涂层具有自修复功能,为自修复超疏水涂层的开发提供了新的研究策略。     

PVDF/SiO2/PDMS涂层超疏水纺织品性能

目的 针对普通纺织品材料防水性和防污性较差的问题,制备具有自清洁功能的超疏水涂层纺织品,并研究其性能.方法 以涤纶织物为基材,通过非溶剂诱导相分离法,使用聚偏氟乙烯和疏水纳米二氧化硅复合液在纺织品表面构筑微纳粗糙结构,采用聚二甲基硅氧烷对其进行疏水化处理,获得自清洁超疏水涂层纺织品.采用扫描电子显微镜、X射线能量散射光谱和视频光学接触角测量仪等对其结构和性能进行表征,并通过机械摩擦、洗涤、酸/碱/盐溶液浸渍和紫外光照等方法对其表面超疏水稳定性进行考察.结果 当聚偏氟乙烯质量分数为2％,疏水纳米二氧化硅质量分数为0.4％,聚二甲基硅氧烷质量分数为1％时,制备的纺织品的表面接触角可达(162.2°±0.8°),滚动角达(2.0°±0.4°),具有优异的超疏水自清洁效应;经72 h酸/碱/盐溶液浸渍、196 h紫外光照、2500次摩擦和120次家庭水洗后,其表面接触角仍大于150°,表现出优异的超疏水稳定性.结论 采用简便的非溶剂相分离法制备的涂层纺织品具有优异的自清洁性能,并且其超疏水性能具有机械耐久性和化学稳定性,有望应用于纺织材料包装领域.     

Superhydrophobic surfaces with hierarchical structure

The physics related to superhydrophobic surfaces has been investigated with attention of its potential applications in a variety of industrial and research fields. In the present study, we report a facile method for preparing superhydrophobic surfaces based on micro and nano scaled structures. Composite thin films are formed by using SiO₂ nanoparticles and poly(dimethylsiloxane) (PDMS). The static contact angle, advancing contact angle, and receding contact angle are measured to investigate the surfaces' water repelling property. The formed SiO₂-PDMS composite films, with different nanoparticle concentrations and sizes, can render the surfaces with superhydrophobicicty, exhibiting large contact angles and small contact angle hysteresis. The composite films are observed by using the Scanning Electron Microscope (SEM). It is demonstrated that the hierarchical structure in micro and nano scale on the surface, plays an important role in prompting the superhydrophobic (water-repelling) properties. Wetting phenomena and related theories are also discussed within the paper.     

SiC/Al复合材料超疏水表面的制备

采用化学刻蚀法在SiC/Al复合材料表面构筑微纳结构,通过SEM和表面接触角测量仪分析刻蚀表面的微观形貌特征及润湿特性,并探讨了其与刻蚀时间之间的关系;借助热震试验评价SiC/Al复合材料超疏水表面的温度骤变耐受特性。结果表明:弥散分布的微米级SiC颗粒的存在使得刻蚀后的SiC/Al复合材料表面易形成由微米级粒状结构和纳米级凹坑结构复合而成的微观结构;氟硅烷修饰后的蚀刻表面的接触角最高达到166.8°,滚动角最低为3°,具有很好的超疏水特性;SiC/Al基超疏水表面具有较好的耐受温度骤变特性。