【作者】 李倩；

【导师】 薛龙建；

【作者基本信息】 武汉大学 ， 材料学， 2021， 博士

【摘要】 在自然界中,具有微纳结构特征的润湿性表面是一些动植物能够赖以生存的关键性因素。通过模仿自然界中的动植物表面微结构,仿生智能表面的相关研究迅速发展。硅橡胶基,特别是聚二甲基硅氧烷(PDMS)基仿生智能表面,由于具有良好的拉伸性和耐化学腐蚀性等性能,获得了广泛关注。但是,随着科技发展和应用需求的增加,人们对于仿生智能各向异性表面的实际应用特性、调控工艺的简化和润湿性定量表征技术提出了更高的要求,改进突破现有仿生智能表面缺乏识别液滴特性、润湿性调控工艺复杂和高黏附表面无法辨别的缺陷,获得更加智能化且润湿性调控工艺简单的新型仿生智能表面成为本领域的研究热点。综上,本论文对PDMS基仿生各向异性表面的液滴酸碱识别性能、新型润湿性调控工艺和高黏附表面定量表征技术进行了探索,具体如下:以荷叶各向同性和蝴蝶翅膀各向异性润湿性为灵感,制备了一种结构可逆调控仿生各向异性表面(TMAS)。TMAS是通过在预先拉伸的PDMS基底薄膜上接枝三角形微柱阵列而成。当液滴在TMAS上朝三角形角(A)方向滚动时,液滴后退角处的三相接触线形态(TCL)呈连续性,液滴无法滚动;朝三角形底边(E)方向滚动时,液滴后退角处的TCL形态呈离散式,液滴易滚动,这赋予了TMAS定向液滴黏附的能力。借助机械应力简单的拉伸-释放,液滴在TMAS上的前进角和后退角处的TCL能够实时同步调控,实现了液滴各向同性(类似荷叶)和定向黏附(类似蝴蝶翅膀)之间的原位可逆转换。基于原位转换特性,TMAS可以从不同的倾斜角度抓取液滴,并通过向E方向旋转释放液滴于倾斜的、垂直的、甚至是倒置的表面上,表现出极大的自由度及容差率。同时,TMAS还具备识别酸碱液滴及检测液滴p H的优异性能。基于对可逆调控仿生各向异性智能表面的深入研究,发现精准调控液固接触面的微观形貌工艺复杂,操作难度较大。基于此,我们通过对已固化良好的PDMS柱状阵列弹性模量与润湿性依赖性研究,发现了非接触基底(B)的弹性模量对PDMS柱状阵列表面的滚动角有着显著影响,提出了调控PDMS柱状阵列表面润湿性的新方法。研究结果证实,PDMS柱状阵列弹性模量的改变不会引起表面接触角的变化;固定基底B的模量不变,柱子阵列(P)的模量由3.2 MPa减小到0.2 MPa,不会引起表面滚动角的改变,滚动角增长率～0%;固定阵列P的模量不变,B的模量由3.2 MPa减小到0.2 MPa,滚动角增大,由～35°增加到-180°,此时样品上下颠倒也无法滚落,滚动角增长率达～600%。柱子阵列高度越高,基底模量越小,滚动角对基底模量的依赖性越强,这种依赖性来源于基底模量对柱子阵列弯曲幅度的影响。基底模量越小,柱子弯曲难度越小,柱子弯曲变形程度越大,液滴在表面的临界后退角越小,液滴滚动角则越大。基于非接触基底PDMS的弹性模量对PDMS柱状阵列表面的滚动角存在显著影响,制备了一种由低模量基底(1.1 MPa)和高模量柱子阵列(2.7 MPa)组成的可调控摩擦力的表面(CFAS),并建立了方便可靠的毛细管传感器技术(CST)以定量表征表面的润湿性。低模量PDMS基底薄膜赋予CFAS优异的形变性能,因而利用机械应力可以实时调节CFAS的周期参数,进而调控其在A方向、E方向和y方向的滚动角,实现多种不同黏附表面之间的转换。利用CST测量液滴在CFAS上的摩擦力以定量区分传统滚动角难以辨别的高黏附CFAS。CST能够测量CFAS的“本征”摩擦力各向异性度,揭示了CFAS摩擦力各向异性度与液滴体积的无依赖性。此外,CST还能解析微结构表面上液滴的详细滑动行为(如粘-滑行为和整个摩擦过程中的三个阶段)。更多还原

【Abstract】 Surfaces with micro-and nanoscale features provide key functions for many plants and insects to survive in nature.By imitating the surfaces of natural creatures,the research of bionic smart surfaces has developed rapidly.Silicone rubber based,especially polydimethylsiloxane(PDMS)based bio-inspired adhesive is a hotspot in research,due to their good flexibility,and chemical resistance.However,PDMS-based bio-inspired smart surfaces still face many challenges for practical application.Preparing smart surfaces with ability to identify property of droplet by simple control process show promise to improve the availability of bio-inspired surfaces in extended fields.So this thesis focuses on the acid/base recognition of droplet on PDMS-based biomimetic anisotropic surfaces,new wettability control mechanisms,and quantitative characterization techniques for highly adhesive surfaces.The details are as follows:A bioinspired surface,termed as TMAS,is presented that is inspired by isotropic lotus leaves and anisotropic butterfly wings.The surface is prepared by simply growing a triangular micropillar array on the pre-stretched thin PDMS film.The array of triangular micropillars offers a long TCL_E in direction A and discrete TCL_A in direction E at the receding front of a droplet on TMAS,which endows TMAS with directional adhesion to water droplet.Therefore,the adhesion of a water droplet on TMAS can be regulated by the opposite rotating.The mechanical stretching-releasing cycle allows the easy,reversible regulation of TCLs at the advancing and receding fronts of a droplet and ultimately allows the transition between isotropic(lotus-leaf-like)and directional adhesion(butterfly-wing-like)of water droplets.TMAS can therefore be used to conveniently pick up and transfer droplet(2～12μL)to horizontal,tilted,vertical,and even upside-down surfaces.Moreover,TMAS has the ability to distinguish acids and bases and tell their p H strengths.Based on the deep study of reversible control bio-inspired anisotropic surface,it is found that the precise regulation of the micro-morphology of liquid-solid contact surface is complicated and difficult to operate.Based on this,we research the dependence of the elastic modulus and wettability of the well-cured PDMS pillar array and find that the non-contact substrate modulus has a significant effect on the sliding angle,and proposed the new mechanism to robust regulate the surface wetting.The research results confirm that the change of the elastic modulus of the PDMS pillar array will not cause the change of the surface contact angle.Fixing the modulus of the substrate B,the modulus of the pillar array P is reduced from 3.2 MPa to 0.2MPa,which will not cause the change of the sliding angle,and the sliding angle growth rate is～0%.While the modulus of P remains unchanged,the modulus of B decreases from 3.2 MPa to 0.2 MPa,and the sliding angle increases from～35° to-180°.In this case,the droplet cannot roll off even if it is turned upside down,and the sliding angle growth rate reaches～600%.The higher the height of the pillar array and the smaller the substrate modulus,the stronger the dependence of the sliding angle on the substrate modulus.This dependence comes from the influence of the base modulus on the bending amplitude of the pillar array.Based on the significant influence of the non-contact substrate modulus on the sliding angle,we have prepared an adjustable friction anisotropic surface(CFAS)composed of a low-modulus substrate(1.1 MPa)and a high-modulus column array(2.7 MPa),and established a convenient and reliable capillary sensor technology(CST)to quantitatively characterize wettability.The low modulus PDMS substrate film endows CFAS with excellent deformation properties.Therefore,the mechanical stress can be used to adjust the periodic parameters of CFAS in real time,and then regulate its sliding angle in the A direction,E direction and y direction to realize the conversion between various high adhesion surfaces.CST is used to measure the friction of droplet on CFAS in order to quantitatively distinguish the surface of droplet high adhesion state which could not be distinguished by traditional sliding angle.CST can also analyze the detailed sliding behavior of droplets on a solid surface(such as stick-slip behavior and three states of friction process).更多还原