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.     

阵列凹坑结构分布与水滴黏附性质的关系

以新鲜玫瑰花花瓣正面为模板, 采用模板印刷法制备具有微米级阵列凹坑和纳米级沟壑结构的聚二甲基硅氧烷(PDMS)薄膜, 通过对该薄膜逐级拉伸改变其微观结构的分布; 采用场发射扫描电子显微镜(SEM)和原子力显微镜(AFM)观察了不同拉伸程度下薄膜表面微观结构的变化, 采用高敏感性微电力学天平测试了样品表面微观结构变化过程中水滴的黏附力, 分析了其微观结构分布与水滴黏附性质的关系; 采用接触角测量仪表征不同拉伸条件下薄膜的浸润性. 结果表明, 随着PDMS薄膜被逐次拉伸, 单位面积内的凹坑结构数目减少, 且凹坑逐渐分离, 凹坑的深度逐渐降低, 水滴更容易浸入到凹坑结构中, 因此水滴与薄膜的黏附力急剧增大; 随着薄膜进一步拉伸, 纳米级沟壑结构会随着凹坑的拉伸而不断伸展, 纳米级沟壑结构的面积增加, 纳米沟壑结构诱捕的空气量逐渐上升, 导致水滴与薄膜表面的接触面积降低, 使得水滴与薄膜的黏附力下降; 继续拉伸PDMS薄膜, 纳米级沟壑结构进一步伸展, 水滴逐渐浸入纳米级沟壑结构中, 水滴与薄膜的黏附力缓慢增大, 当水滴完全进入到纳米级沟壑中时, 水滴与薄膜的黏附力达到极大值, 此时继续拉伸PDMS薄膜, 纳米级沟壑结构随着拉伸程度的增加继续伸展, 水滴与薄膜的接触面积稍有减少, 黏附力将有所下降, 直至薄膜被完全破坏. 由此可见, 微米级凹坑结构和纳米级褶皱结构的分布是影响PDMS薄膜对水滴黏附性质的主要因素.     

含氟硅丙烯酸酯乳液超疏水膜中疏水基团的梯度分布与表面微观结构研究

利用含氟疏水基团的梯度分布,结合草莓形纳米SiO2粒子提供的双重粗糙表面,制备了具有类"荷叶效应"的超疏水涂膜,水接触角达(174.2±2)°,滞后角几乎接近0°.通过原子力显微镜、扫描电镜和水接触角的测试对膜表面形貌及疏水性能进行了表征;探讨了其表面微观结构与表面疏水性能的关系.草莓形复合粒子在膜表面的无规则排列赋予涂膜表面不同等级的粗糙度,使水滴与涂膜表面接触时能够形成高的空气捕捉率,这种微观结构与疏水基团的梯度分布相结合,赋予了含氟硅丙烯酸酯乳液涂膜表面超疏水性能.     

双级微结构上二氧化硅粒子对微注压成型PP表面润湿特性的影响

提出一种柔性复制法,采用微注射压缩(μ-ICM)成型具有微拓扑结构的仿生聚丙烯(PP)表面.通过复制模板上的双级微结构,所成型的PP材料表面上呈现具有锥形顶面的双级微结构,即微棱和高纵横比的微锥体.由于微锥体之间的间隙较大,水滴浸润其间隙的上方,这使该表面呈现中等黏附的超疏水特性.在μ-ICM过程中,涂覆在模板上的二氧化硅纳米粒子(SNPs)被转移到熔体中,并牢牢附着于微结构表层,赋予其表面亚微米或微米粗糙度,形成多层次微结构.在附着有亲水SNPs的微结构上,高表面自由能使水滴完全浸润微锥体之间的间隙,表面的水接触角为161.9°、滚动角大于90°,呈现极高黏附的超疏水特性(花瓣效应);在附着有疏水SNPs的微结构上,水滴受疏水SNPs的排斥而减弱与表面之间的黏附作用,表面的水接触角为163.5°、滚动角为3.5°,呈现极低黏附的超疏水特性(荷叶效应).     

刚-柔嵌段共聚物在有序排列的微米圆盘表面自组装构筑多级结构

在材料表面构筑聚合物多级结构可以显著提升其性能并赋予新的性能,但是目前已有的制备方法较为繁琐,需要开发简单易行的新方法。结合聚苯乙烯(PS)的可控蒸发组装和聚(γ-苄基-L-谷氨酸酯)-聚乙二醇(PBLG-b-PEG)刚-柔嵌段共聚物溶液自组装方法,在硅片表面构建了梯度排列且表面具有纳米条纹的微米圆盘多级结构。采用光学显微镜、原子力显微镜(AFM)和接触角测量仪等对微结构形貌及硅片的表面润湿性进行了表征。PS溶液经可控蒸发自组装在硅片表面形成梯度变化的微米圆点图案,经热处理及溶剂清洗后,得到微米圆盘。通过溶液自组装方法,PBLG-b-PEG在PS微米圆盘表面形成有序排列的周期性纳米条纹。材料的接触角随着图案表面微结构从半球状圆点到表面平整的圆盘再到表面带有纳米条纹的圆盘的变化持续降低。     

蝴蝶翅膀表面水滴各向异性黏附性质

采用扫描电子显微镜(SEM)观察了双带闪蝶(Morpho Achilles)翅膀表面的微观形貌, 通过样品的表观接触角表征了其浸润性, 采用高敏感性微电力学天平比较了水滴在蝴蝶翅膀表面不同方向运动时受到的黏附力. 实验结果表明, 水滴沿着干燥的蝴蝶翅膀鳞片堆叠方向运动时受到的黏附力要明显小于其它方向运动时受到的力, 且受力较稳定; 当蝴蝶翅膀被水滴浸润后, 水滴沿着湿润的蝴蝶翅膀鳞片堆叠方向运动时受到的黏附力接近甚至大于逆着鳞片堆叠方向运动时受到的力.     

玫瑰花花瓣微观结构与水滴黏附性质的关系

利用环境扫描电镜(ESEM)分别观察了新鲜、枯萎的玫瑰花花瓣正、反两面的微观形貌,并通过测量样品的表观接触角表征了其浸润性,采用高敏感性微电力学天平测试了样品表面的粘附力,分析了玫瑰花花瓣微观结构与水滴粘附性质的关系.实验结果表明,微米结构主要影响玫瑰花花瓣的超疏水性,而纳米结构则是导致玫瑰花花瓣具有高粘附力的关键原因.     

梯度接触角表面的构建与应用

梯度接触角是梯度表面张力的反映,固体表面的润湿性由表面化学组成和表面微观形貌共同决定。通过表面化学组成和表面微观形貌的梯度化,可制备接触角变化范围不同的梯度接触角表面。本文综述了梯度接触角表面在液滴移动、微流体流动和生物吸附等领域中的应用。梯度接触角表面具有的不平衡杨氏力是促进液滴移动的主要原因,而表面所产生的接触角滞后则阻碍液滴移动;在生物学领域,梯度接触角表面会造成蛋白质和细胞选择性吸附或黏附。最后,简要探讨了梯度接触角表面存在的问题和发展方向。     

霸王鞭和麒麟掌叶片的表面微结构及超疏水性

霸王鞭(Euphorbia antiquorum)和麒麟掌(Euphorbia neriifolia var. cristata)是2种特殊的叶片, 正面不疏水而叶片背面超疏水的沙漠植物. 本文通过接触角测试仪、 电子显微镜和表面张力测试仪分别对叶片的超疏水性、 表面微观形貌和表面黏附力进行了测试和表征. 采用模板法, 以聚乙烯醇为模板、 以聚苯乙烯为基底制备仿叶片背面结构的聚苯乙烯薄膜, 并对薄膜表面的超疏水性、 表面微观形貌和表面黏附力进行了测试和表征, 发现这2种叶片背面的平均间距为1~3 μm的层片状微观结构可以构建出具有超疏水高黏附力特性的表面.     

形状记忆聚合物表面微结构及黏附性能的可逆调控

采用模板法在形状记忆聚合物表面构筑了微纳米等级结构,获得了一种具有低黏附性的超疏水表面.在外压作用下,表面微结构发生坍塌,失去超疏水性,同时呈高黏附性.在120℃热处理后,表面微结构恢复到原始状态,同时表面恢复到低黏附状态.通过外压及热处理过程可实现对表面微结构及其黏附性能的可逆调控.研究结果表明,表面不同的微结构状态赋予了表面不同的黏附性能,即在原始表面上,液滴处于低黏附的Cassie态,而在坍塌结构表面上水滴处于高黏附的Wenzel态.     

Localized Deposition of Chitosan as Matrix for Enzyme Immobilization

A local electrodeposition method was developed for chitosan by exploiting a pH gradient between a macroscopic electrode (the support) and a much smaller counter electrode. The deposition was confined either by using the direct mode of scanning electrochemical microscopy (SECM) or by performing the deposition in channels of a microfluidic network. The roughness was characterized by noncontact scanning force microscopy. The availability of amino groups at the surface of the microstructures was visualized after labeling by confocal laser scanning microscopy. The enzyme glucose oxidase could be entrapped during the electrochemical deposition and showed activity as seen by SECM images.     

Improving hydrophilicity and protein antifouling of electrospun poly(vinylidenefluoride-hexafluoropropylene) nanofiber membranes

<正>Poly(vinylidenefluoride-hexafluoropropylene)(PVDF-HFP) nanofiber membranes with improved hydrophilicity and protein fouling resistance via surface graft copolymerization of hydrophilic monomers were prepared.The surface modification involves atmospheric pressure glow discharge plasma(APGDP) pretreatment followed by graft copolymerization of poly(ethylene glycol) methyl ether methacrylate(PEGMA).The success of the graft modification with PEGMA on the PVDF-HFP fibrous membrane is ascertained by X-ray photoelectron spectroscopy(XPS) and attenuated total reflectance Fourier transform infrared measurements(ATR-FTIR).The hydrophilic property of the nanofiber membranes is assessed by water contact angle measurements.The results show that the PEGMA grafted PVDF-HFP nanofiber membrane has a water contact angle of 0°compared with the pristine value of 132°.The protein adsorption was effectively reduced after PEGMA grafting on the PVDF-HFP nanofiber membrane surface.The PEGMA polymer grafting density on the PVDF-HFP membrane surface is measured by the gravimetric method,and the filtration performance is characterized by the measurement of water flux.The results indicate that the water flux of the grafted PVDF-HFP fibrous membrane increases significantly with the increase of the PEGMA grafting density.     

Preparation and characterization of polyaniline/polysulfone nanocomposite ultrafiltration membrane

Novel nanocomposite membrane was prepared through the filtration of polyaniline (PANI) nanofiber aqueous dispersion with polysulfone (PS) ultrafiltration (UF) membrane. Scanning electron microscope (SEM) images showed that PANI nanofiber layer was formed on the PS membrane surface. Atomic force microscopy (AFM) analysis indicated that the nanocomposite membrane had rougher surface than the PS substrate membrane. Compared with the PS substrate membrane, the nanocomposite membrane had much better permeability for the good hydrophilicity of PANI nanofiber layer, and had almost the same rejection performance. In addition, the nanocomposite membrane had positive surface potential under acidic condition because PANI could be protonated easily by acid. During the filtration of BSA solution, the nanocomposite membrane showed much better antifouling performance than the substrate membrane for the hydrophilicity and steric hindrance effect of its nanofiber layer. Moreover, under acidic solution condition, strong electrostatic repulsion between PANI nanofibers and BSA existed and improved membrane antifouling performance further.     

Sensitive Hydrazine Electrochemical Biosensor Based on a Porous Chitosan–Carbon Nanofiber Nanocomposite Modified Electrode

A novel electrochemically-based biosensor was developed for the determination of hydrazine by modifying a glassy carbon electrode with an aqueous dispersion of carboxylic group-functionalized carbon nanofiber/chitosan solution, and then absorbing hemoglobin on the surface of chitosan-carbon nanofibers. Nafion was used to coat the hemoglobin membrane. The interactions of hemoglobin and the nafion/chitosan-carbon nanofibers were investigated by ultraviolet-visible absorption, infrared, and circular dichroism spectroscopies. The results indicated that the native structure of hemoglobin was retained post-immobilization. The circular dichroism results showed that the α-helical structure of hemoglobin was preserved though a small change was observed in the presence of the nafion/chitosan-carbon nanofibers. The modified nanofibers were further characterized by scanning electron microscopy, electron impendence spectroscopy, and cyclic voltammetry. The electrocatalytic mechanism of hemoglobin to the oxidation of hydrazine was investigated and an irreversible diffusion-controlled electrode process was obtained. The electron transfer rate constant (k_s), transfer coefficient (α), and Michaelis–Menten constant (K_m) were also evaluated. The peak current of the catalytic oxidation was linear with hydrazine concentration from 3.722 × 10^?5 to 1.601 × 10^?3 molar with a correlation coefficient of 0.995. The detection limit was estimated to be 2.7 micromoles per liter. The sensitivity, stability, and reproducibility of the nafion/hemoglobin/chitosan-carbon nanofiber/glassy carbon electrode for the oxidation of hydrazine were also investigated.     

Fabrication and electrochemical instrumentation of redox‐active nanofiber mat for polyaniline incorporated with poly(imide sulfonate)

In this study, we demonstrate the fabrication of an electrochemically active nanofiber mat that is a composite of high‐performance poly(imide sulfonate) (PIS) and polyaniline (PANI). First, a nonconductive nanofiber mat comprising nanofibers having diameters of ca. 300 nm was fabricated by the electrospinning of ionomeric PIS in N,N‐dimethylformamide (DMF). Then, the nanofibers were modified using PANI, which was synthesized by the oxidative polymerization of aniline, yielding an electrochemically active nanofiber mat having a diameter of ca. 350 nm. It was confirmed that PANI was successfully incorporated onto the PIS nanofiber mats by X‐ray photoelectron spectroscopy. Subsequently, we conducted electrochemical measurements of the PANI‐modified nanofiber mats using a tailor‐made attachment in which the working electrode gently comes in contact with the nanofiber mat surface. This attachment was observed to be widely useful in the cyclic voltammetry measurements related to redox‐active nanofibers. These observations are expected to contribute to the advancements in application development of the electrochemically active nanofiber mats.     

二氧化硅@聚合物同轴纳米纤维

The preparation and formation mechamsm ot silica/polyvinylpyrrolidone(PAN) coaxial nanofibers were presented in this paper. The PVP-PAN composite nanofibers were obtained via an electrospinning technique, while SiO2 nanoparticles were prepared according to a Stoeher method. The measurements of water contact angle(WCA), the compared results of silica coating PVPPAN composite nanofibers with PAN nanofibers indicate that much PVP resided on the composite nanofiber surface, which resuks in the occurrence of SiO2@polymer coaxial nanofibers due to the formation of hydrogen bonding between silica and composite nanofibers and subsequent adsorption of silica on the fiber surface.     

Development of electrospun metallic hybrid nanofibers via metallization

The metallized hybrid nanofiber webs were prepared by using a combined technology of electrostatic spinning and metallization. The electrospun polyurethane (PU) nanofibers were metallized with different thicknesses of copper layer via metal vapor deposition technique. The thickness of the copper layer, which ranges from 10 to 100 nm, was monitored and controlled. The resultant metallized hybrid nanofiber webs were characterized using field emission scanning electron microscopy (FE‐SEM), wide angle X‐ray diffraction (WAXD), and thermogravimetric analysis (TGA). FE‐SEM images demonstrated that the nanoscaled copper layers are well deposited on the surface of the PU nanofibers. TGA result indicated that the thermal stability of the metallized hybrid PU nanofibers was dramatically enhanced due to the barrier effects of thin metallic copper layer. WAXD data confirmed that the crystalline copper layers were well deposited onto the PU nanofibers. Moreover, the mechanical properties of the metallized hybrid PU nanofiber webs were increased with increase in the thickness of deposited copper layer. Unlike the organic PU nanofiber webs, it was observed that the metallized hybrid PU nanofiber webs showed higher conductive properties depending on the thickness of the deposited copper layer. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamically Controllable Emission of Polymer Nanofibers: Electrofluorescence Chromism and Polarized Emission of Polycarbazole Derivatives

Electrochemical polymerization of a series of N‐alkyl‐2,7‐di(2‐thienyl)carbazoles in acetonitrile was performed to obtain conjugated polymers with fluorescence. Scanning electron and atomic force microscopies revealed that the surface morphology of the polymer films significantly depends on the alkyl chain lengths of the polymers. Particularly, a homopolymer bearing hexyl groups and copolymers with an average alkyl chain length of six carbon atoms show nanofiber morphology. The polymer nanofibers were stacked on a substrate electrode. The fluorescence of the polymer nanofiber film was tunable with application of voltage, with good repeatability. The X‐ray diffraction pattern of the fibers showed the structural order. The polymer nanofibers thus prepared showed an electrochemically driven change in polarized photoluminescence.