Direction-dependent adhesion of water strider's legs for water-walking

We report the direction-dependent adhesion of water strider's legs for fleetly walking on water surface. The flexibly oriented setae of legs involving the hierarchical micro/nanostructure tune effectively the solid–liquid–air three phase interfaces in two opposite directions: the direction along the setae and opposite the setae, generating different adhesion dependent on the direction. A model is proposed to elucidate the underlying mechanism of water-walking based on direction-dependent adhesion induced by the orientation of the aligned setae. This finding will improve our understandings of the interaction between the oriented structured surface and water surface, and is significant to boost biomimetic structured surface that can be applied into microfluidics and aquatic microdevices.     

两性离子自组装仿生表面的制备、 表征及抗黏附性能

设计与合成了磺酸甜菜碱型的两性离子化合物: N,N-二甲基氨甲酸乙酯基丙基三乙氧基硅烷磺酸内盐(SiNNS), 利用红外光谱(FTIR)和氢核磁共振波谱(¹H NMR)对其分子组成与结构进行了表征. 通过自组装技术将SiNNS分子构筑在玻璃基材表面, 形成了模拟细胞外层膜的仿生表面. 利用原子力显微镜(AFM)、 X光电子能谱(XPS)和接触角测量仪对表面的形貌特征、 化学组成和润湿性进行了表征. 以空白玻璃为对照样品, 研究了这一表面的防雾性能和抗细菌黏附性能. 结果表明, 所制备的两性离子自组装仿生表面具有超亲水性和水下超疏油特性, 其水滴接触角为9.2°, 水下油滴接触角接近180°; 与对照样品相比, 两性离子自组装表面具有优异的防雾性与抗细菌黏附性.     

花生叶表面的高黏附超疏水特性研究及其仿生制备

花生是一种常见的豆科作物.与低黏附超疏水的荷叶不同,花生叶表面同时具有超疏水和高黏附特性.水滴在花生叶表面的接触角为151±2°,显示出超疏水特性.此外,水滴可以牢固地附着在花生叶表面,将花生叶翻转90°甚至180°,水滴均不会从表面滚落,显示了良好的黏附性(黏附力超过80μN).研究发现,花生叶表面呈现微纳米多级结构,丘陵状微米结构表面具有无规则排列的纳米结构.花生叶表面特殊的微纳米多尺度结构是其表面呈现高黏附超疏水特性的关键因素.结合实验数据,对花生叶表面特殊浸润性机理进行了简要阐述.受此启发,利用聚二甲基硅氧烷复形得到了与花生叶表面微结构类似的高黏附疏水表面.本文以期为仿生制备高黏附超疏水表面提供新思路.     

蒸发自组装法制备聚苯乙烯胶体晶体

采用乳液聚合法制得亚微米级聚苯乙烯单分散微球,并用蒸发自组装法在乳液气-液界面进行自上而下的层层组装,制得了厚度在450μm以上的三维有序胶体晶体。结果表明,影响胶体晶体有序性的关键因素是对蒸发速度的控制,促使胶体晶体规则排列的最主要作用力为溶液的毛细管力。在胶体晶体组装末期,随着溶剂量的减少,空间阻力逐渐增大,微球对流能力下降,造成胶体晶体的有序性降低。     

Enhanced Property of Thin Cuprous Oxide Film Prepared through Green Synthetic Route

Thin cuprous oxide films have been prepared by chemical vapor deposition (pulsed spray evaporation-chemical vapor deposition) method without post-treatment. The synthesis ofcuprous oxide was produced by applying a water strategy effect. Then, the effect of water on the morphology, topology, structure, optical properties and surface composition of the obtained films has been comprehensively investigated. The results reveal that a pure phase of Cu₂O was obtained. The introduction of a small quantity of water in the liquid feedstock lowers the band gap energy from 2.16 eV to 2.04 eV. This finding was mainly related to the decrease of crystallite size due to the effect of water. The topology analyses, by using atomic force microscope, also revealed that surface roughness decreases with water addition, namely more uniform covered surface. Moreover, theoretical calculations based on density functional theory method were performed to understand the adsorption and reaction behaviors of water and ethanol on the Cu₂O thin film surface. Formation mechanism of the Cu₂O thin film was also suggested and discussed.     

Synchronized motion of a mobile boundary driven by a camphor fragment

The synchronized self-motion of a camphor fragment and a mobile boundary on a water surface depending on the initial conditions and the asymmetry of the boundary was investigated. When a camphor fragment, which showed unidirectional rotation, was surrounded by a circular ring as a symmetric mobile boundary on a water surface, the circular ring also rotated but in the direction opposite to that of the camphor fragment. The velocity of the rotation of the mobile ring varied depending on the anisotropy of the shape of the ring. When a camphor fragment was placed on the inside of a circular ring floating on the water surface, the ring and camphor fragment exhibited translational motion without rotation. These characteristics of synchronized self-motion are discussed in relation to the surface tension as the driving force and convective flow due to the gradient of the surface-active camphor layer.     

Sol–gel synthesis of IPTES and D10H consisting fluorinated silane system for hydrophobic applications

In this study, new fluorinated silane system was prepared by adding hydroxyl terminated Fluorolink D10H oligomer to 3-isocyanatopropyltrietoxysilane. The obtained silane system was independently composed with 3-Glycidyloxypropyltrimethoxysilane and 3-Glycidyloxy-propyltriethoxysilane. Then the prepared two different coating solutions were applied to glass surface by spin-coating method. The chemical bonding between groups in system was investigated by FTIR analysis. The elemental composition of coatings was determined by using EDX analysis. Their structure and surface properties were analyzed by scanning electron microscopy, atomic force microscopy, contact angle measurement and UV–vis spectrophotometer. The amounts of fluorine on the coatings prepared with IPTES-D10H-GLYEO and IPTES-D10H-GLYMO were 33 and 34 %wt, respectively. Transparent coatings with smooth surface and uniform thickness were obtained. The coatings had nanoscale roughness. The contact angles of coatings for water were range from 103° to 110°, and for n-hexadecane were range from 59° to 62°.     

Non-Aqueous Assay System for Phenobarbital Using Biomimetic Bulk Acoustic Wave Sensor Based on a Molecularly Imprinted Polymer

ABSTRACT

A new biomimetic bulk acoustic wave (BAW) sensor based on a molecularly imprinted polymer (MIP) was fabricated and applied for the determination of phenobarbital The MIP was synthesized using phenobarbital as the template molecule and methacrylic acid as the functional monomer by the non-covalent method. In absolute ethanol, the sensor exhibited good selectivity and sensitivity. A linear relationship between 9.0×10^?8 M and 5.0×10^?5 M was revealed. The determination limit was 5.0×10^?8 M. In harsh chemical environments such as high temperature, organic solvent, bases, acids, etc., the sensor still exhibited long-time stability. Satisfactory results of real sample assay were obtained by the proposed method.     

Nature's design of hierarchical superhydrophobic surfaces of a water strider for low adhesion and low-energy dissipation

The mechanics of wet adhesion between a water strider's legs and a water surface was studied. First, we showed that the nanoscale to microscale hierarchical surface structure on striders' legs is crucial to the stable water-repellent properties of the legs. The smallest structure is made for the sake of a stable Cassie state even under harsh environment conditions, which sets an upper limit for the dimension of the smallest structure. The maximum stress and the maximum deformation of the surface structures at the contact line are size-dependent because of the asymmetric surface tension, which sets a lower limit for the dimension of the smallest structure. The surface hierarchy can largely reduce the adhesion between the water and the legs by stabilizing the Cassie state, increasing the apparent contact angle, and reducing the contact area and the length of the contact line. Second, the processes of the legs pressing on and detaching from the water surface were analyzed with a 2D model. We found that the superhydrophobicity of the legs' surface is critically important to reducing the detaching force and detaching energy. Finally, the dynamic process of the legs striking the water surface, mimicking the maneuvering of water striders, was analyzed. We found that the large length of the legs not only reduces the energy dissipation in the quasi-static pressing and pulling processes but also enhances the efficiency of energy transfer from bioenergy to kinetic energy in the dynamic process during the maneuvering of the water striders. The mechanical principles found in this study may provide useful guidelines for the design of superior water-repellent surfaces and novel aquatic robots.     

掺杂态聚苯胺蜂窝状有序多孔薄膜的制备及形成机制的探讨

近年来,由于微米、亚微米及纳米级有序多孔结构薄膜可以用于催化、生物培养基材、分离或吸附介质、光子晶体等诸多方面从而引起了科学家们极大的研究兴趣^[1～6].微制作是使材料表面具有新性能的重要手段,激光刻蚀及其相关技术已经被应用于不同表面的微图案化和微器件的制作^[7],另外,还可通过自组装技术进行多孔薄膜的制备^[8,9].Francois等^[10]于1994年首次提出了水辅助方法(Water-A ssisted Fab-rication),即在高湿度的环境下,以冷凝水滴为模板,在固体基片上制备了孔径分布均一,排列紧密的蜂窝状有序多孔薄膜.继而人们对此方法做了进一步的研究,不仅突破了最初的聚苯乙烯及其共聚物体系^[10～13],而且使用双亲共聚物^[14]、聚离子复合物^[15]和TiO₂前驱体的混合物^[16]等成功地获得了蜂窝状有序多孔薄膜,同时系统地研究了成膜体系及成膜条件对形成蜂窝状有序多孔薄膜的影响,并对形成机制进行了探讨.聚苯胺是典型的导电高分子,有关聚苯胺有序多孔结构薄膜的研究已有报道^[17～19].本文采用水辅助方法,在高湿度环境下,使用4-十二烷基苯磺酸掺杂的聚苯胺(PANI-DBSA)为成膜材料,制备了双层蜂窝状有序多孔薄膜,并通过原子力显微镜(A FM)对薄膜的形貌和电学性质进行了表征.同时在已有成膜机制的基础上,提出了该双层蜂窝状有序多孔薄膜的形成机制.     

Spontaneous film formation from a polymer solution

An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor.The thickness of the mechanically stable films is less than 0.5 m. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.     

Mathematical modeling of a hydrophilic cylinder floating on water

In this paper, a hydrostatic model of the surface profile anchored to the upper edge of a vertical cylinder is proposed to explain why coins can float on water surface. The sharp edge of a cylinder is thus modeled as a round smooth surface on which the contact line may be anchored at a position according to the weight of the cylinder. The mathematical model of the surface profile is established based on the hydrostatics and a third order ordinary differential equation is resulted. Numerical solution of the model demonstrates under practical conditions the existence of the surface profiles that provide reasonable uplifting force at the contact line so that the force is available for floating coins on water surface. The proposed model explains the obviously enlarged apparent contact angle and the edge effect in the literature. The numerical simulation is found in very good agreement with the experimental data in the literature.     

A new method for producing “Lotus Effect” on a biomimetic shark skin

Nature has long been an important source of inspiration for mankind to develop artificial ways to mimic the remarkable properties of biological systems. In this work, a new method was explored to fabricate a superhydrophobic dual-biomimetic surface comprising both the shark-skin surface morphology and the lotus leaf-like hierarchical micro/nano-structures. The biomimetic surface possessing shark-skin pattern microstructure was first fabricated by microreplication of shark-skin surface based on PDMS; and then it was treated by flame to form hierarchical micro/nano-structures that can produce lotus effect. The fabricated biomimetic surfaces were characterized with scanning electron microscopy (SEM), water contact angle measurements and liquid drop impact experiments. The results show that the fabricated dual-biomimetic surface possesses both the vivid shark-skin surface morphology and the lotus leaf-like hierarchical micro/nano-structures. It can exhibit excellent superhydrophobicity that the contact angle is as high as 160° and maintain its robustness of the superhydrophobicity during the droplet impact process at a relatively high Weber number. The mechanism of the micromorphology evolution and microstructural changes on the biomimetic shark-skin surface was also discussed here in the process of flame treatment. This method is expected to be developed into a novel and feasible biomimetic surface manufacturing technique.     

Preferential affinity of the components of liquid mixtures at a rigid non-polar surface: enthalpic and entropic driving forces

The modulation of the properties of lipid membranes by polyhydroxylated cosolutes such as sugars is a phenomenon of considerable biological, technological and medicinal relevance. A few years ago, we proposed the sugar-like mechanism--binding driven by the release of water molecules--as an attempt to rationalize the preferential affinity of carbohydrate molecules compared to water molecules for the surface of lipid bilayers, which is presumably related to the bioprotective action of these compounds. The goal herein is to gain a better understanding of the driving force underlying this mechanism, in terms of specific interactions or effects, as well as in terms of the energy-entropy partitioning. This is done in the simplest possible context of an apolar rigid-wall model representing the membrane, and mixtures of closely related and possibly artificial species in solution, namely monomers or dimers of Lennard-Jones particles, water with physical or reduced charges, and hydroxymethyl groups. The results indicate that although the sugar-like mechanism seems phenomenologically reasonable, the main driving force underlying this mechanism is not the entropy gain upon releasing water molecules into the bulk, as originally suggested, but rather the hydrophobic effect. Note that the latter effect is a generic concept and may in principle involve both a solvent release and an interaction component, depending on the solute considered.     

WATER TRANSPORT BY A SPREADING SURFACTANT IN FINE DISPERSE MATERIALS

A surface active substance (surfactant) spreads on the water film lying on the surface of fine disperse materials (clay, oxides), with lower velocity than on the surface of bulk water and on coarse materials (sand).

The spreading surfactant carries the underlying water although the surface is not continuous and water is present as a thin film.

The ratio of the transported water to the spread surfactant decreases with increasing specific surface, being > 10⁴ on sand surface and < 10 on fine disperse materials (clay, oxides).

The amount of transported water increases with increasing specific surface and increasing water film thickness. The driving force for water transport is the surface pressure; the presence of another surfactant is therefore prejudicial for the spreading and transport of underlying water.

The water transport by the spreading surfactant is accompanied by the streaming potential, which is inversely related to the specific surface.     

原位透射电子显微镜观察电荷驱动的氧化物纳米颗粒水中自组装

以四氧化三钴Co_3O_4纳米棒为研究对象,我们利用液体环境透射电子显微镜,原位观察了四氧化三钴纳米棒在水中的自组装过程。研究发现在电子束辐照的水环境下,四氧化三钴纳米棒的晶面存在互补式自组装现象。随着纳米棒之间的距离越来越近,纳米棒之间的相对运动速率逐渐增加,纳米棒之间的相互作用力逐渐增加。通过进一步分析纳米棒的形貌发现,纳米棒的暴露晶面大多数为{100}、{110}以及{111}晶面,而Co_3O_4属于极性氧化物,这些晶面往往会带有一定的电荷。在液体环境下,正是由于这些易暴露面都带有不同大小的电荷,在晶面电荷的驱动下,电荷属性相反的四氧化三钴纳米棒会互相吸引,形貌结构上进行互补,实现快速驱动的纳米棒之间自组装。     

Xyloglucan in cellulose modification

Xyloglucans are the principal polysaccharides coating and crosslinking cellulose microfibrills in the majority of land plants. This review summarizes current knowledge of xyloglucan structures, solution properties, and the mechanism of interaction of xyloglucans with cellulose. This knowledge base forms the platform for new biomimetic methods of cellulose surface modification with applications within the fields of textile manufacture, papermaking, and materials science. Recent advances using the enzyme xyloglucan endo-transglycosylase (XET, EC 2.4.1.207) to introduce varied chemical functionality onto cellulose surfaces are highlighted.     

Oscillatory motion of coke in deactivated HZSM-5 zeolite

We have observed motion of coke in deactivated HZSM-5 with the displacement vector alternately directed toward the outer surface of the zeolite crystals and into the interior of the zeolite structure. The driving force for the oscillations is the higher chemical potential of massive carbon μ_m at 500 °C than for carbon clusters. The switching mechanism involves an alternating jumpwise change in the value of Δμ.     

Synthesis and Studies on Surface Active Water Soluble Derivatives of Siloxane Oligomers

Abstract

We report the synthesis of cationic water-soluble siloxanes by reacting aminosiloxanes with dimethyl, n-dodecyl 3-chloro-2-hy-droxypropyl quaternary ammonium iodide (DDCQA). Tetramethyl disiloxane on hydrosilation with allyl amine in the presence of hex-achloroplatinic acid/IPA gave bis(3-aminopropyl) octamethyltetra-siloxane. In addition, formation of Si-H containing oligomeric siloxanes were detected during this reaction and the extent of formation of the oligomers was found to depend upon the concentration of platinum. The oligomerization reaction was explained by dehydrogenative coupling of Si-H groups in the presence of platinum catalyst. A plausible mechanism for formation of aminosiloxane and the Si-H oligomers were proposed. Alternatively, cyclic Si -H containing siloxanes on polymerization using butyl lithium gave oligomeric Si-H containing siloxanes, which were hydrosilated to give aminosiloxanes. The quaternary aminosiloxanes synthesized showed lowering in surface tension of water to 26 mN/m.