A geometry controllable approach for the fabrication of biomimetic hierarchical structure and its superhydrophobicity with near-zero sliding angle

A simple, geometry controllable method is presented for fabricating multiscale hierarchical polymer structures that exhibit superhydrophobic water-repellent properties with near-zero sliding angle over a large area. A UV-assisted micromolding technique is used to create a microtexture with an ultraviolet (UV)-curable resin containing Al(2)O(3) nanoparticles. A subsequent treatment of ultraviolet ozone (UVO) leads to the formation of nanoscale roughness over the as-formed microstructured surface, resulting in a dual-scale surface texture similar to a lotus leaf, in a reproducible manner. After hydrophobization with a self-assembled monolayer (SAM) in the liquid phase, this hierarchical surface exhibits stable superhydrophobic characteristics, having a water contact angle close to 160° and a contact angle (CA) hysteresis as low as 1°. These characteristics did not change even after exposure to ambient conditions for 6?months.     

玻璃基底上的蛋白质微接触压印图型化

研究了一种将胶原Ⅰ型蛋白通过微接触压印技术图型化于玻璃基底表面的方法.采用标准光刻工艺制备印章母版,并运用反应离子刻蚀设备对印章表面进行氧等离子体处理,以期改善印章表面亲水性能.将涂敷了胶原Ⅰ型蛋白,并经返潮处理的印章以50 g/cm^2大小的力与玻璃表面接触10 s,得到蛋白质微图型.结果表明,采用反应离子刻蚀技术能显著改善聚二甲基硅氧烷（PDMS）印章表面的亲水性.表面亲水性得到改善的PDMS印章,在经过湿盒返潮后,再进行微接触压印得到的蛋白质微图型其质量得到显著提高.     

CaCO3/SiO2复合粒子涂层的表面结构及其疏水性能研究

以机械高速搅拌法制备了具有草莓结构的CaCO₃/SiO₂复合粒子,并对其进行了表面修饰改性.利用聚硅氧烷的自组装功能,将制备的复合粒子与硅氧烷一起制备了具有“荷叶效应”的超疏水涂层,静态水接触角达169°,滚动角约为2°.通过扫描电镜观察涂层的表面微观形貌,发现该涂层具有微米-纳米相结合的双层粗糙结构.微米凸起的粒径在2～3μm左右,纳米凸起的粒径约为200nm左右,与荷叶具有类似的结构排布方式.通过原子力显微镜和接触角的测试,探讨了表面微观结构、涂层粗糙度和涂层疏水性能之间的关系.结果表明：复合粒子构成的非均相界面的水接触角符合Cassie模型.复合粒子赋予涂层的双微观粗糙结构与自组装成膜硅氧烷的低表面能的协同效应,使涂层具有了优良的超疏水性能.     

Low‐density Polyethylene Films Loaded by Titanium Dioxide and Zinc Oxide Nanoparticles as a New Active Packaging System against Escherichia coli O157:H7 in Fresh Calf Minced Meat

Antibacterial packaging is introduced as a new method to prevent microbial food spoilage. Antibacterial effects of TiO₂, ZnO and mixed TiO₂–ZnO nanoparticle‐coated low‐density polyethylene (LDPE) films on Escherichia coli PTCC1330 were investigated. Bactericidal efficiency of 0.5%, 1% and 2% TiO₂ and ZnO nanoparticles and also 1% mixed TiO₂–ZnO nanoparticles with ratios of 25/75, 50/50 and 75/25 were tested under ultraviolet (UV) and fluorescent lights at two states: films alone and fresh calf minced meat packed. Maximum colony‐forming unit (CFU) reduction of 99.8% and 99.7% were obtained using 1% and 2% ZnO nanoparticle‐coated LDPE film under fluorescent light for films alone as well as 99.8% and 99.6% for fresh calf minced meat packed. 90.3% and 51.8% CFU reduction were recorded for 1% TiO₂ nanoparticle‐coated LDPE films in the presence of UV light at direct contact with bacteria and fresh calf minced meat packed, respectively. Maximum CFU reductions of 96% and 64.1% were obtained using 50/50 ratio of TiO₂/ZnO nanoparticles at the presence of UV light for film alone and fresh calf minced meat packed, respectively. ZnO nanoparticle‐coated LDPE films were identified as the best case to improve shelf life and prevent E. coli growth in fresh calf minced meat.     

Direct printing of silver nanoparticles by an agarose stamp on planar and patterned substrates

In this study, we have used an agarose stamp to conduct direct printing of silver nanoparticles, nanowires and nanoplates on both planar and structured substrates. Nanoparticle solution could be first coated on an agarose stamp, and then transferred to a planar substrate. Micro-patterns comprising metal nanoparticles could be printed on planar substrates without the formation of residual layers. Thus a three-dimensional metal microstructure could be easily fabricated. The patterning of electrodes by printing Ag nanowires directly on TiO(2) was also demonstrated to fabricate resistive random access memory (RRAM) devices by all-solution-processing methods. By using a flat agarose stamp, the patterns printed on the microstructured substrates were quite different from those on the nanostructured substrates. On the microstructured substrates, direct printing could print silver nanoparticles onto the protrusion surface, and could print silver layers as thick as several microns, useful for high conductivity electrodes. On the substrates with nanostructures such as photonic crystals or nano-gratings, direct printing could transfer nanoparticles into the grooves or cavities only due to the contact of the agarose stamp with the groove or concavity surface. A new approach to fabricate metal wire grid polarizers was further demonstrated. A nanoporous agarose stamp has a good potential for printing using nanoparticle suspension.     

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.     

仿生超疏水棉织物的制备与表面分析

以荷叶表面微/纳米结构为参考模型,先用硅溶胶处理天然棉织物,再用N-β-氨乙基-γ-氨丙基聚二甲基硅氧烷(ASO-1)对其进行修饰,获得了微/纳米二元粗糙的超疏水织物,水滴在该织物表面接触角可达160.5°。场发射扫描电子显微镜(FE-SEM)观察发现超疏水纤维表面存在大量均匀分布的纳米微凸体。接触角分析表明织物织造过程中形成的微米级粗糙度和ASO-1膜的存在是织物疏水的主要原因,纳米微凸体能减少纤维与水的接触面积,提高水在纤维表面的接触角,使织物由疏水转变为超疏水。最后用X射线光电子能谱仪(XPS)证实了纤维表面SiO2粒子和ASO-1膜的存在。     

Layer-by-Layer assembly of TiO2 nanoparticles for stable hydrophilic biocompatible coatings

Stable, super-hydrophilic (water contact angle approximately equal to 0 degrees) titanium dioxide nanoparticle thin films have been obtained on substrates with different initial wettability such as glass, poly(methyl methacrylate) and poly(dimethyl siloxane) using layer-by-layer nano-assembly method. Titanium dioxide nanoparticles were alternated with poly(styrene sulfonate) to form films of thickness ranging from 11 nm to 220 nm. The hydrophilicity of these thin films increases with increasing number of deposited PSS/TiO2 bilayers. It was found that 2, 5 and 20 layers were needed to form super-hydrophilic TiO2 coating on glass, PMMA and PDMS respectively. Oxygen plasma treatment of substrate surfaces enhanced the formation of homogeneous TiO2 films and accelerated the formation of hydrophilic layers. Super-hydrophilicity has been shown to be unique to PSS/TiO2 films as compared with other polyelectrolyte/nanoparticle layers, and UV irradiation may restore hydrophilicity even after months of storing of the samples. Biocompatibility of TiO2 nanoparticle films has been demonstrated by the successful cell culture of human dermal fibroblast.     

Peanut Leaf Inspired Multifunctional Surfaces

Nature has long served as a source of inspiration for scientists and engineers to design and construct multifunctional artificial materials. The lotus and the peanut are two typical plants living in the aquatic and the arid (or semiarid) habitats, respectively, which have evolved different optimized solutions to survive. For the lotus leaf, an air layer is formed between its surface and water, exhibiting a discontinuous three‐phase contact line, which resulted in the low adhesive superhydrophobic self‐cleaning effect to avoid the leaf decomposition. In contrast to the lotus leaf, the peanut leaf shows high‐adhesive superhydrophobicity, arising from the formation of the quasi‐continuous and discontinuous three‐phase contact line at the microscale and nanoscale, respectively, which provides a new avenue for the fabrication of high adhesive superhydrophobic materials. Further, this high adhesive and superhydrophobic peanut leaf is proved to be efficient in fog capture. Inspired by the peanut leaf, multifunctional surfaces with structural similarity to the natural peanut leaf are prepared, exhibiting simultaneous superhydrophobicity and high adhesion towards water.     

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.     

Plasma modification of polyolefin surfaces

In order to functionalize the surface of blown low‐density polyethylene (LDPE) and cast polypropylene (CPP) films, and ultimately to maximize the attachment of active molecules onto them, the optimum treatment parameters of capacitively‐coupled radio‐frequency (13.56 MHz) oxygen plasma were investigated by using contact angle, toluidine blue dye assay, X‐ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR‐FTIR). Contact angle values of LDPE and CPP samples decreased significantly after oxygen plasma treatment. They further decreased as the plasma power level increased. The treatment time had no substantial effect on contact angle value. The optimum treatment conditions for LDPE and CPP films for maximizing carboxyl functionality without causing observable surface changes were found to be 200 W/200 mTorr and 250 W/50 mTorr, respectively, when treated for 3 min. The maximum carboxyl group concentration obtained with LDPE and CPP films were 0.46 and 0.56 nmol/cm², respectively. The percent of oxygen atoms on the surface of plasma‐treated LDPE and CPP films was determined by XPS analysis to be 22.6 and 28.7%, respectively. The ATR‐FTIR absorption bands at 1725–1700 cm^?1 confirmed the presence of carboxylic acids on LDPE and CPP films. By exposing the plasma‐treated sample to air rather than water and treating films repeatedly with oxygen plasma, a higher carboxyl group concentration could be obtained. Copyright © 2008 John Wiley & Sons, Ltd.     

Patterning of TiO2 particles on poly(dimethyl siloxane) films by using proton irradiation and liquid-phase deposition process

Micropatterning of titanium dioxide (TiO2) on the surface of thin poly(dimethyl siloxane) (PDMS) films was described by means of proton irradiation and liquid-phase deposition (LPD) techniques. The surface of thin PDMS films was irradiated with accelerated proton ions through a pattern mask in the absence or presence of oxygen in order to create hydrophilically/hydrophobically patterned surfaces. The results of the surface analysis revealed that the PDMS films irradiated at the fluence of 1 x 10(15) ions cm-2 in the presence of oxygen showed the highest hydrophilicity. The LPD of TiO2 particles on the patterned PDMS film surface showed a selective deposition of TiO2 on the irradiated regions, leading to well defined TiO2 micropatterns. The crystal structure of the formed TiO2 films was found to be in an anatase phase by X-ray diffraction analysis. This process can be applied for patterning various metal and metal oxide particles on a polymer substrate.     

Superhydrophobic polymer films via aerosol assisted deposition — Taking a leaf out of nature's book

Aerosol assisted deposition of three sets of polymer films based on commercially available resins was achieved on various substrates. The films were characterised using a range of methods, including water contact and slip angle to determine water repellent properties. The aerosol assisted deposition inside the chemical vapour deposition reactor was unique in generating a highly rough superhydrophobic surface with water contact angles up to 170°. During the deposition process, two of the polymers were cured resulting in the development of high surface morphology. It was observed that the polymer that did not cure did not develop such a rough surface resulting in a lower water contact angle (∼ 99°). The superhydrophobic films had a Cassie-Baxter type wetting with water failing to penetrate the surface porosity, water spraying on the surface would bounce off. These films had exceptionally low slide angles of ca 1-2° from the horizontal.     

Replication of surfaces of natural leaves for enhanced micro-scale tribological property

In this paper, we report on the replication of surfaces of Lotus and Colocasia leaves onto thin polymeric films using a capillarity-directed soft lithographic technique. The replication was carried out on poly(methyl methacrylate) (PMMA) film spin coated on silicon wafer using poly(dimethyl siloxane) (PDMS) molds. The friction properties of the replicated surfaces were investigated at micro-scale in comparison with those of PMMA thin film and uncoated silicon wafer. The coefficients of friction of the replicated surfaces were almost five times lower than those of the PMMA thin film and four times lower than those of the uncoated silicon wafer. The superior micro-tribological properties of the replicated surfaces could be attributed to the reduced real area of contact projected by the surfaces.     

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.     

类荷叶表面疏水结构的材料表面制备

利用纳米/微米复模成型的方法,制备了荷叶表面微乳突状疏水结构的聚乙烯醇(PVA)和聚苯乙烯(PS)阴模模具,并利用阴模复模成型在聚二甲基硅烷(PDMS)表面制备了类荷叶的表面结构.扫描电子显微镜(SEM)的观察表明PDMS材料表面上制得的类荷叶结构与荷叶表面的微乳突结构有较好的一致性,而PVA阴模在保持微观结构上更有优势.通过对水滴在PDMS材料表面接触角的测量,证明了在制备有类荷叶表面结构的PDMS材料表面上,水滴的接触角可以得到显著提高.     

Self-organized meso-patterning of soft solids by controlled adhesion: elastic contact lithography

The surface of a soft elastic film becomes unstable and deforms when a rigid flat plate is brought into its contact proximity, without application of any external pressure. These isotropic undulations have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. The wavelength is independent of the adhesive interactions and the mechanical properties of the film. We present here a mini-review of our recent work on techniques of aligning, modulating, and ordering the instability structures by the use of simple 1-D patterned stamps, by changing the stamp-surface separation, by slow shearing of a flat stamp and by confining the instability in soft narrow channels. The generality of the technique for different soft materials is illustrated by patterning cross-linked polydimethylsiloxane (PDMS), aluminum coated PDMS and hydrogels films. Use of a flexible stamp such as a metal foil provides enhanced conformal contact by adhesive forces, which aids large area patterning without critically maintaining a parallel configuration and uniform pressure between the stamp and the film. The technique has the potential to develop into a new soft lithography tool--"Elastic Contact Lithography" suitable for rapid, large area micron and sub-micron self-organized patterning of a variety of soft materials without any special equipments.     

Patterning Hydrophobic Surfaces by Negative Microcontact Printing and Its Applications

Here, a negative microcontact printing method is developed to form hydrophilic polydopamine (PDA) patterns with micrometer resolution on hydrophobic including perfluorinated surfaces. In the process of the negative microcontact printing, a uniform PDA thin film is first formed on the hydrophobic surface. An activated polydimethylsiloxane (PDMS) stamp is then placed in contact with the PDA‐coated hydrophobic surface. Taking advantage of the difference in the surface energy between the hydrophobic surface and the stamp, PDA is removed from the contact area after the stamp release. As a result, a PDA pattern complementary to the stamp is obtained on the hydrophobic surface. By using the negative microcontact printing, arrays of liquid droplets and single cells are reliably formed on perfluorinated surfaces. Microlens array with tunable focal length for imaging studies is further created based on the droplet array. The negative microcontact printing method is expected to be widely applicable in high‐throughput chemical and biological screening and analysis.     

Reinforcement of polysiloxane with superhydrophobic nanosilica

We systemically report on a new method for producing reinforced poly(dimethylsiloxane) (PDMS) with superhydrophobic nanosilica. Firstly, we rationally designed to synthesize a series of well-dispersed hydrophobic nanosilica by using hexadecyltrimethoxysilane (HDTMS) as the treatment agent. Fourier transforms infrared (FT-IR) spectrum, thermo-gravimetric analysis (TGA), and contact angle (CA) measurement were used to characterize the grafting degree of HDTMS grafted onto the surface of nanosilica. Subsequently, we employed these modified hydrophobic nanosilica to further reinforce PDMS. The properties of as-prepared modified nanosilica filled PDMS composites were thoroughly investigated by rheological test, scanning electron microscopy (SEM), TGA, and dynamic mechanical analysis (DMA). We have found that these as-prepared superhydrophobic nanosilica exhibit uniform dispersity in the PDMS matrix, and their composites exhibit good mechanical properties and obvious advantage on thermal stability compared with those of the pure silica filled PDMS composites.     

Superhydrophobic films from raspberry-like particles

We report a robust procedure for preparing superhydrophobic hybrid films on which the advancing contact angle for water is about 165 degrees and the roll-off angle of a 10-muL water droplet is 3 +/- 1 degrees . Dual-size surface roughness, which mimics the surface topology of self-cleaning plant leaves, originates from well-defined silica-based raspberry-like particles that are covalently bonded to an epoxy-based polymer matrix. The roughened surface is chemically modified with a layer of poly(dimethylsiloxane) (PDMS). The robustness and simplicity of this procedure may make widespread applications of so-prepared superhydrophobic films possible.