仿生超疏水性表面的生物应用

自然给科学家和工程师带来仿生的灵感和启发. 近年来, 受自然界中荷叶的启发, 在充分考虑表面形貌和化学组成协同效应的基础上, 人们已经制备出许多仿生超疏水性表面, 这些表面在抗结冰、微流体、生物相容性等领域具有很多潜在的应用价值. 仿生超疏水性表面在生物领域的应用逐渐崭露头角, 研究发现, 超疏水性表面所俘获的空气能够减缓药物释放的速率, 因此利用此类表面作为药物的载体有望实现长期供药. 超疏水特性能在一定程度改善和提高生物体与材料表面之间的相互作用, 例如, 血小板几乎不在超疏水表面上进行粘附和活化避免了造成血栓和血凝, 因此仿生超疏水性表面可用于制备人造血管和与血液相接触的仪器. 细胞和生物分子在不同特殊润湿性表面具有不同的行为和现象, 如粘附、繁殖、吸附等差异, 这有助于进一步探索研究细胞和生物分子的信息功能, 是当前仿生超疏水性表面应用的重要研究方向之一. 本综述简单介绍了经典的润湿模型, 重点总结了仿生超疏水表面在生物领域的应用, 其主要包括控制药物释放、提高血液相容性、蛋白质吸附研究、细胞行为研究、生物分子和细胞微图案化等. 最后, 对仿生超疏水性表面在生物领域研究应用进行了展望.     

仿生超疏水性表面的最新应用研究

近年来,除了荷叶表面,更多具有特殊润湿性的动植物表面同样受到关注。通过研究这些表面微观结构,人们成功地仿生制备出各种功能化超疏水表面,从而更好地满足工业中实际应用的需要。该综述简单地介绍了表面润湿的基本模型和最新的几种特殊表面结构,重点介绍近几年仿生超疏水表面应用的最新研究进展,主要包括超疏水表面在超疏油、表面润湿转换、外界刺激下的润湿行为调控、微流体、抗结冰等方面的应用。最后,对超疏水表面研究的未来发展进行了展望。     

仿生超疏水性表面的研究进展

仿生超疏水性表面的研究是化学模拟生物体系研究中的一个新领域。荷叶等植物叶面的超疏水现象为我们在不同基底上制备仿生超疏水性表面提供了实践基础。本文给出荷叶等三种植物叶面的超疏水性和微观结构,阐述了仿生超疏水性表面的研究进展。     

功能化超疏水材料的研究与发展

超疏水材料由于其独特的自清洁性能在日常生活和工业领域中有着广泛的应用前景。目前,随着单一功能化超疏水材料研究的成熟,超疏水材料性能的多样性,如透明性、耐磨耐久性、润湿性转换等,在基础研究和实际应用中受到了广泛的关注。透明超疏水涂层除了具备一般超疏水涂层的性能外还具有良好的透光性;而提高超疏水材料的耐磨耐久性在实际应用中具有极为重要的意义;润湿性转换则扩展了超疏水表面在油水分离等方面的应用。虽然已有较多关于超疏水材料的研究,但仍然无法满足人们对超疏水表面功能性的需求,因此研究功能化超疏水涂层具有更加深远的意义。本文综述了超疏水材料在透明性,耐磨耐久性,润湿性转换以及混合物分离等方面的研究进展,并展望了超疏水材料领域未来的研究热点和发展方向。     

超疏水膜表面构造及构造控制研究进展

本文就表面构造对膜表面亲、疏水性的最新研究成果进行了概括,表面化学成分及化学结构聚集态是获得超疏水膜的基础,表面的形貌和微构造是维持超疏水性质的保障。利用含氟材料极低的表面能,将表面化学结构的聚集态,表面形貌微观构造及排列方式进行有机结合,将会获得理想的超疏水材料。     

超疏水涂膜的研究进展

超疏水涂膜以其独特的性能,在国防、工农业生产和日常生活中有着广泛的应用前景。但目前的制备技术制约了其在建筑外墙涂料等大型设施方面的应用。探索如何采用简单有效的方法构造和调控涂膜的双微观结构,从而获得性能持久优异的超疏水性涂膜,并有效应用于生产和生活的各个方面是这一领域研究的最终目标。本文就超疏水材料表面理论的发展和近几年来超疏水膜制备技术取得的新成果进行了概括,并指出制备超疏水涂膜存在的问题和发展方向。利用表面能极低的含氟材料,将溶胶－凝胶、相分离技术和自组装梯度功能等技术有机结合,获得适宜的表面粗糙度和微观构造,是实现超疏水涂膜工业化生产的可行途径。     

超疏水性表面的制备及应用进展

近年来,受荷叶、水黾腿、壁虎脚等天然超疏水生物表面特性的启发,研究者们进行了大量仿生超疏水表面材料的制备及应用研究。超疏水性表面因其特殊的微纳分层结构,具有自清洁、防覆冰、防腐蚀、减阻等优异性能。本文阐述了表面润湿、疏水的基本机理,以及超疏水表面研究的理论基础,对超疏水表面制备的最新研究进展进行了综述,并揭示了研究中存在的问题。最后,介绍了超疏水表面在涂料、织物、防腐、抗菌及防雾等领域中的应用,展望了其未来的研究方向和前景。     

微纳结构超疏水表面的浸润性分析及设计

微纳复合结构超疏水表面在防污、流动减阻、防冰等领域具有广阔的应用前景，超疏水表面主要通过设计表面化学性质和微观几何结构来获得.合理设计保持表面润湿态的稳定性是其性能发挥的关键.以"液滴-超疏水表面"系统为研究对象，基于最小能原理分析了四种稳定润湿形态，指出影响润湿状态的本征接触角和微观结构参数（相对柱距、相对柱高）.推导了本征接触角的计算公式并对常见材料的本征接触角进行了讨论.结合四种润湿态方程，绘制了随着相对柱距和相对柱高的润湿云图，并将润湿云图归纳为"一点三线六区四状态".分析了相对柱距和相对柱高对浸润状态的影响，结果表明较大的本征接触角、较小的相对柱距和较大的相对柱高能够减小浸润状态发生转变的临界参数，从而拓展超疏水表面的区域范围，有利于超疏水表面的稳定性.利用文献数据验证了上述润湿云图能够准确反映出润湿形态.在上述工作基础之上总结提炼了超疏水表面设计的一般思路.研究结果可为超疏水表面的设计提供理论依据和技术基础.     

仿生超疏水材料的构建及应用研究

<正>所谓超疏水表面是指与水的静态接触角>150°、滚动角<10°的固体表面。随着科技的进步和社会的发展,超疏水材料以其独特的润湿性能在印刷包装工业中具有广泛的应用前景。对自然界中天然超疏水表面微观结构的研究表明构建具有一定粗糙度的表面微观结构是获得超疏水表面的重要途径。本论文从超疏水固体表面微细结构的角度出发,提出了几种构建超疏水功能涂层更为简单、高效的制备方法,并研究了相应表面的润湿性能及在疏水涂层及油水分离方面的应用。具体研究内容如下:     

具有超疏水表面的硅/二氧化硅层次结构薄膜

目前报道的硅基材料的超疏水表面主要是通过制备粗糙微观结构,并在其表面修饰表面能相对较低的有机物两个步骤来实现的,在户外等实际环境中应用时存在由于表面修饰有机物的降解而逐渐失去超疏水性的问题.本工作以液态金属锡作为生长衬底,通过化学气相沉积(CVD)法制备了一种具有超疏水性能的硅基薄膜结构.利用扫描电镜(SEM),透射电镜(TEM)以及X射线衍射(XRD)等手段对产物的表面形貌和组成结构进行分析发现,薄膜表面由竖直生长的硅/二氧化硅(Si/SiO2)核壳层次结构组成.采用Cassie理论模型对其超疏水性能的产生提出了可能的解释.发现构成薄膜表面的Si/SiO2层次结构单元的形貌是影响超疏水性能的重要因素.相对于以前报道的硅基材料的超疏水表面,这种新结构的超疏水性能不依赖于表面化学修饰,有望拓宽硅基材料的应用环境.     

Anisotropic wetting on checkerboard-patterned surfaces

A series of surfaces with microscale checkerboard patterns consisting of continuous central lines and discontinuous lateral lines were fabricated. The surface wetting properties of these checkerboard patterns were found to be anisotropic. The central continuous lines were found to have a strong influence on the dynamic wetting properties and moving trajectories of the water droplets. The droplets move more easily in the direction parallel to the central continuous lines and less easily in the direction perpendicular to the central continuous lines. Meanwhile, the droplets' moving path tends to incline toward the central continuous lines from a tilting direction. When the microsurface was modified with a layer of nanowire, the surface wettability was found to be isotropic and superhydrophobic.     

Effects of rugged nanoprotrusions on the surface hydrophobicity and water adhesion of anisotropic micropatterns

A facile laser-etching method was used for the one-step creation of various controllable dimensions of anisotropic micropatterns consisting of an alternating arrangement of microgrooves and microstripes with rugged nanoprotrusions, which after modified with fluoroalkylsilane reagent, showed perfect isotropic superhydrophobicity without apparent CA hystereses, water adhesion, and drag resistance, other than the conventional view of anisotropic surface microstructures with anisotropic surface dewetting. The detailed experiments and analyses have indicated that the introduction of the rugged nanoprotrusions on the surface of microstripes provided ideal 3D roughness, which could not only enhance the apparent contact angles close to 180 degrees by the "point" contact fashion to maximally reduce the liquid-solid contact area but, most importantly, make droplets easily roll off the surface without apparent CA hysteresis by regulating the triple-phase contact line (TCL) to become extremely discrete. These findings would be helpful in understanding the role of complex micro- and nanostructures on natural superhydrophobic biosurfaces and guiding the design of perfect artificial superhydrophobic materials for technological innovations such as the raindrop easy-cleaning, aquatic super-floating, and drag-reducing coatings.     

Application of Nano-Hydroxyapatite Derived from Oyster Shell in Fabricating Superhydrophobic Sponge for Efficient Oil/Water Separation

The exploration of nonhazardous nanoparticles to fabricate a template-driven superhydrophobic surface is of great ecological importance for oil/water separation in practice. In this work, nano-hydroxyapatite (nano-HAp) with good biocompatibility was easily developed from discarded oyster shells and well incorporated with polydimethylsiloxane (PDMS) to create a superhydrophobic surface on a polyurethane (PU) sponge using a facile solution–immersion method. The obtained nano-HAp coated PU (nano-HAp/PU) sponge exhibited both excellent oil/water selectivity with water contact angles of over 150° and higher absorption capacity for various organic solvents and oils than the original PU sponge, which can be assigned to the nano-HAp coating surface with rough microstructures. Moreover, the superhydrophobic nano-HAp/PU sponge was found to be mechanically stable with no obvious decrease of oil recovery capacity from water in 10 cycles. This work presented that the oyster shell could be a promising alternative to superhydrophobic coatings, which was not only beneficial to oil-containing wastewater treatment, but also favorable for sustainable aquaculture.     

Induced detachment of coalescing droplets on superhydrophobic surfaces

Coalescence of a falling droplet with a stationary sessile droplet on a superhydrophobic surface is investigated by a combined experimental and numerical study. In the experiments, the droplet diameter, the impact velocity, and the distance between the impacting droplets were controlled. The evolution of surface shape during the coalescence of two droplets on the superhydrophobic surface is captured using high speed imaging and compared with numerical results. A two-phase volume of fluid (VOF) method is used to determine the dynamics of droplet coalescence, shape evaluation, and contact line movement. The spread length of two coalesced droplets along their original center is also predicted by the model and compared well with the experimental results. The effect of different parameters such as impact velocity, center to center distance, and droplet size on contact time and restitution coefficient are studied and compared to the experimental results. Finally, the wetting and the self-cleaning properties of superhydrophobic surfaces have been investigated. It has been found that impinging water drops with very small amount of kinetic impact energy were able to thoroughly clean these surfaces.     

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.     

Deformation of isotropic and anisotropic liquid droplets dispersed in a cellulose liquid crystalline derivative

In this work we study the strain-induced deformation of both isotropic and anisotropic liquid droplets dispersed in a liquid crystalline cellulose matrix. We have produced two types of acetoxypropylcellulose (APC) solid films one with a droplet dispersion of the commercial liquid crystal E7 from Merck, and another with a droplet dispersion of silicone oil. To produce the solid films a solution of APC (60%wt) in dimethylacetamide (DMAc) with 15%wt of either the commercial nematic liquid crystal E7 or the silicone oil was prepared. After homogenization the phase separated solutions were submitted to a shear flow mechanical field and casted onto a Teflon plate. We performed mechanical uniaxial stress-strain tests in the free standing films recording continuously the strain and images of the deformed droplets. The mechanical tests were carried out using a mini stress-strain testing machine apparatus and an Olympus optical polarizing microscope with an attached CCD camera. The images obtained from the mechanical tests for each value of the imposed strain were then analyzed comparing the images of deformed droplets with those of the undeformed ones, extracting in this way the local strain field. The droplet deformation data obtained show, as expected, significant differences in the local strain field when stretching parallel and perpendicular to the initial shear direction. No significant differences were found in the local strain fields obtained from the silicone oil and the E7 droplets films. The local strain fields variation with the imposed strain are compared with the predictions of the theory developed for nematic elastomers by Warner and Terentjev (Liquid crystal elastomers. Clarendon Oxford Press, Oxford, 2003).     

Transport of liquids using superhydrophobic aerogels

The experimental results of the studies on the transportation of water droplets on a superhydrophobic silica aerogel-powder-coated surface are reported. The superhydrophobic silica aerogels were prepared using sol-gel processing of methyltrimethoxysilane (MTMS) precursor, methanol (MeOH) solvent, and base (NH4OH)-catalyzed water followed by supercritical drying using methanol solvent. The molar ratio of NH4OH/MTMS, H2O/MTMS, and MeOH/MTMS were varied from 1.7x10(-1) to 3.5x10(-1), 2 to 8, and 1.7 to 14, respectively, to find out the best-quality aerogels in terms of higher hydrophobicity and high droplet velocity. A specially built device was used for the measurement of velocity of water droplet of size 2.8 mm (+/-0.2 mm) on an inclined surface coated with superhydrophobic aerogel powder. Liquid marbles were prepared by rolling water droplets on aerogel powder and the marble(s) velocities on a noncoated inclined surface were compared with that of the water droplets. It was observed that the microstructure of the aerogel affects the droplet as well as marble velocities considerably. For an aerogel with uniform and smaller particles, the water droplet and marble velocities were observed to be maximum, i.e., 144 and 123 cm/s, respectively, whereas for the aerogels with bigger and nonuniform particles, the water droplet and marble velocities were observed to be minimum, i.e., 92 and 82 cm/s, respectively. The results have been discussed by taking into account the contact angles and microstructural observations.     

Orientation and anchoring effects in stretched polymer dispersed nematic liquid crystals

The induction of liquid crystal orientation through mechanical stretching was investigated for polymer dispersed liquid crystals (PDLCs) by means of infrared dichroism. Using a nematic liquid crystal BL006 and polyacrylic acid as the polymer matrix, it was possible to stretch the PDLC films with BL006 in either the isotropic or the nematic phase. After cooling the films under strain to room temperature, the molecular orientation of BL006 was found to be much higher for films that contained isotropic liquid droplets of BL006 at the time of stretching than for films that had nematic droplets. Stretching PDLC films with isotropic droplets results in no molecular orientation, but the orientation is induced during the subsequent cooling when BL006 goes through the isotropic-to-nematic phase transition. Interestingly for PAA/BL006, the nematic director orients along the long axes of the elongated droplets despite liquid crystal anchoring perpendicular to the polymer interface.     

Orientation and anchoring effects in stretched polymer dispersed nematic liquid crystals

The induction of liquid crystal orientation through mechanical stretching was investigated for polymer dispersed liquid crystals (PDLCs) by means of infrared dichroism. Using a nematic liquid crystal BL006 and polyacrylic acid as the polymer matrix, it was possible to stretch the PDLC films with BL006 in either the isotropic or the nematic phase. After cooling the films under strain to room temperature, the molecular orientation of BL006 was found to be much higher for films that contained isotropic liquid droplets of BL006 at the time of stretching than for films that had nematic droplets. Stretching PDLC films with isotropic droplets results in no molecular orientation, but the orientation is induced during the subsequent cooling when BL006 goes through the isotropic-to-nematic phase transition. Interestingly for PAA/BL006, the nematic director orients along the long axes of the elongated droplets despite liquid crystal anchoring perpendicular to the polymer interface.     

Several surfaces with special wettability: Influence on spreading and motion of W/O emulsion droplets

Physical and chemical modifications were made on the surface of the aluminum sheet to change the surface properties and superhydrophobic–hydrophilic wettability gradient surface was made on the perspex surface by using microstructure-pattering technique and self-assembled-monolayer method. By using high-speed video camera system and optical tensiometer, this paper discusses the influence of special surfaces with different wettability on spreading and motion of water, oil, and W/O emulsion droplets both experimentally and theoretically. In addition, the paper also discusses the influence of the superhydrophobic–hydrophilic wettability gradient on fluidity of W/O emulsion droplets and the coalescence process of droplets. The results showed that the contact angle of W/O emulsion droplets on the modified surfaces was related to the water and oil distribution at the three-phase line. On the wettability gradient surface, the droplet moved spontaneously when the droplet was located at the junction of the gradient. A quasi-steady theoretical model was used to analyze the driving and resistant forces acting on a droplet to improve the understanding of the self-transport behavior of the droplets.