形状记忆磁性润滑表面的制备及对超顺磁液滴的滑动操控

将磁性粒子与形状记忆聚合物复合,通过设计渐变式构型构筑了梯度形状磁性材料,并与润滑涂层相结合,制备了一种磁性润滑表面.在磁性梯度的作用下,超顺磁液滴在表面上能够自发定向运动.借助于材料形状记忆效应对表面区域形态进行可逆调控,进一步展示了超顺磁液滴自发定向运动过程中的启停开关式控制,实现了将液滴定向自发运输与启停控制相结合.考察了磁性粒子含量对材料形状记忆性能的影响,以及区域形态调控尺寸与液滴滑动性能间的相互关系.机理分析进一步阐明磁场梯度提供的定向驱动力促使液滴定向自发输运,表面区域形态控制的可逆调控则可以在液滴运动过程中增加/消除黏滞阻力,基于两种因素的协同作用,可以实现对超顺磁液滴运动的智能操控.     

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.     

形状记忆聚合物表面水下油黏附性的可逆调控

采用模板法在形状记忆聚合物表面获得一种具有形状记忆特征的表面微结构, 在氧等离子作用下, 表面呈现低黏附的水下超疏油特性. 在外压作用下, 表面微结构发生坍塌, 失去水下超疏油性, 同时表面对油滴呈高黏附特征. 在120 ℃热处理后, 表面微结构恢复到了原始状态, 在等离子进一步作用下, 表面即可恢复到最初的低黏附水下超疏油状态. 因此通过外压、 热处理及等离子作用即可实现对表面微结构及其水下油黏附性能的可逆调控. 研究表明, 表面不同的微结构状态赋予表面不同的黏附性能, 在原始表面液滴处于低黏附的Cassie态, 而在坍塌结构表面水滴处于高黏附的Wenzel态.     

亲水性形状记忆环氧树脂制备及表面浸润性调控

采用聚乙二醇(PEG)对间苯二甲胺(MXDA)固化的TDE-85环氧树脂体系进行改性,制备了亲水性形状记忆环氧树脂,结合微形貌构筑和热响应方式对树脂表面浸润性进行智能调控.结果表明,PEG的引入有效地增加了TDE-85环氧树脂的亲水性.PEG的最佳含量为20%(质量分数)时,树脂表面的接触角为54°,实现了环氧树脂从原始TDE-85/MXDA固化体系表面的疏水性(接触角为108°)到TDE-85/MXDA/PEG固化体系表面亲水性的转变;改性后树脂的玻璃化转变温度Tg为71℃,形状固定率和回复率分别为96.10%和99.97%,表明得到的树脂具有良好的形状记忆性能.进一步采用模板法在树脂表面构筑了微阵列结构,基于形状记忆效应,通过对表面微阵列形态的控制,实现了环氧树脂表面介于亲水性(接触角为51°)与超亲水性(接触角为0°)间的可逆浸润性智能调控.     

微纳米复合的各向异性结构表面的液滴驱动

通过聚二甲基硅氧烷和Co粉混合物模板复型、外加磁场控制法和氧化锌纳米线水热生长法,制备了微纳米复合的各向异性结构表面.该结构表面规整分布着间距为400μm的倾斜锥状纤维,其底部和顶部直径分别约为200和80μm,长度约为1 mm.锥状纤维的表面覆有氧化锌纳米线,其直径约为80~100 nm,长度约为1μm.该表面呈疏水性,接触角约为142.5°,且具有浸润性各向异性的特征.实验结果表明,液滴在该表面可以定向弹跳或在垂直振动情况下定向滚动,为设计驱动液滴的功能性材料提供了思路.     

液滴模板法制备颗粒材料过程中介尺度结构调控的研究进展

以液滴模板法来制备颗粒材料,可通过对液滴以及颗粒界面介尺度结构的形成与反应的定向调控来实现对固体颗粒功能材料的高效制备和性能强化。深入研究液滴和固体颗粒界面介尺度结构与反应-扩散过程的相互关系及其定向调控规律,揭示反应与扩散过程的机制及其耦合,对于实现反应过程强化与理性调控具有重要的意义。本文主要介绍了液滴模板法制备颗粒材料过程中的介尺度结构调控的研究新进展,着重介绍了界面两亲分子聚集态介尺度结构对液滴形貌的定向调控及对液滴稳定性的影响、以及液滴界面传递与反应对颗粒材料介尺度结构的定向调控,以期为液滴模板法合成颗粒材料的反应过程强化与理性调控提供科学指导。     

超疏水表面微纳二级结构对冷凝液滴最终状态的影响

从超疏水表面(SHS)上初始冷凝液核长大、合并、形成初始液斑开始,分析计算了冷凝液斑变形成为Wenzel或Cassie液滴过程中界面能量的变化,并以界面能曲线降低、是否取最小值为判据,确定冷凝液滴的最终稳定状态.计算结果表明:在只有微米尺度的粗糙结构表面上,冷凝液滴的界面能曲线一般都是先降低再升高,呈现Wenzel状态;而当表面具有微纳米二级粗糙结构,且纳米结构的表面空气面积分率较高时,冷凝液滴的能量曲线持续降低,直至界面能最小的Cassie状态,因此可以自发地形成Cassie液滴.还计算了文献中具有不同结构参数的SHS上冷凝液滴的状态和接触角,并与实验结果进行了比较,结果表明,计算的冷凝液滴状态与实验观察结果完全吻合.因此,微纳二级结构是保持冷凝液滴在SHS上呈现Cassie状态的重要因素.     

界面现象与液滴聚并

报导了一个受溶质Marangoni效应影响的液滴聚结的迟缓现象．采用示踪液滴法，对滴加在正戊醇水溶液表面、受自发界而流控制的硝基乙烷液滴的运动和存在状态进行了研究．结果显示，在一定体系中溶质Marangoni效应可导致液滴的悬浮态，并对液滴的聚并产生显著影响．由于界面状态的不同，示踪液滴也表现出完全不同的动力学特征．基于以上认识对液滴运动速率的计算得到了合理的结果．     

超疏水表面上冷凝液滴发生弹跳的机制与条件分析

使用液滴合并前后的体积和表面自由能守恒作为两个限制条件,确定了合并液滴的初始形状,即为偏离平衡态的亚稳态液滴,具有缩小其底半径而向平衡态液滴转变的推动力.进而分析了液滴变形过程中的推动力和三相线(TPCL)上的滞后阻力,建立了液滴变形的动态方程并进行了差分求解.如果液滴能够变形至底半径为0mm的状态,则根据该状态下液滴重心上移的速度确定液滴的弹跳高度.不同表面上冷凝液滴合并后的变形行为的计算结果表明,光滑表面上的液滴合并后,液滴只能发生有限的变形,一般都在达到平衡态之前就停止了变形,因此冷凝液滴不会发生弹跳;粗糙表面上的Wenzel态液滴的三相线上的滞后阻力更大,因而液滴更难以变形和弹跳;具有微纳二级结构表面上只润湿微米结构,但不润湿纳米结构的部分Wenzel态液滴能够变形至Cassie态,但没有明显的弹跳;只有在纳米或微纳二级结构表面上的较小Cassie态液滴合并后,液滴易于变形至底半径为0mm的状态并发生弹跳.因此,Cassie态合并液滴处于亚稳态,并且其三相线上的移动阻力很小,是导致冷凝液滴弹跳的关键因素.     

纳米结构表面上冷凝液滴的生长模式及部分润湿液滴的形成机制

分析并计算了纳米结构表面上冷凝液滴按照不同途径长大的过程中液滴能量的增加速率, 并以能量增加最小为判据来确定液滴的生长途径. 结果表明, 纳米结构内形成的冷凝液斑在初期按接触角(CA)增加的模式生长时, 其能量增加速率远低于其它模式, 于是, 初始液斑先按增大接触角、并保持底面积不变的模式生长, 直至液滴达到前进角状态. 此后, 沿接触角增加的模式长大所导致的能量增加速率开始远高于其它生长模式, 于是液滴三相线开始移动, 底面积开始增加, 但接触角保持不变. 液滴所增加的底面积可以呈润湿或复合两种状态, 分别形成Wenzel 液滴及部分润湿液滴, 前者的表观接触角一般小于160°, 而后者则明显大于160°. 液滴的生长模式及其润湿状态均与纳米结构参数密切相关, 仅当纳米柱具有一定高度、且间距较小时, 冷凝液滴才能呈现部分润湿状态. 最后, 本模型对纳米结构表面上冷凝液滴润湿状态的计算结果与绝大部分实测结果相一致, 准确率达到91.9%, 明显高于已有公式的计算准确率.     

Smart Multiple Wetting Control on ZnO Coated Shape Memory Polymer Arrays

Recently, surfaces with intelligent wetting controllability have aroused increased attention. Endowing the surface with stimuli-responsive surface chemistry and tunable surface microstructure can achieve a surface with smart wetting performances. However, almost all existing surfaces only focused on single surface chemistry or micromorphology, thus to achieve smart multiple wetting regulation is still difficult. Herein, we report a ZnO coated shape memory polymer(SMP) surface, and the surface chemistry and micromorphology can be synergistically regulated. ZnO can provide adjustable surface chemistry under UV irradiation, and SMP can offer tunable micromorphology due to its shape memory effect(SME). Based on the combined effect between the above two features, surface wetting performance can be smartly regulated among multiple states. Moreover, due to the excellent controllability of the surface, the application in directional droplet transportation was also demonstrated. This paper offers a new surface with tunability in both surface chemistry and micromorphology, and given the excellent wetting controllability, the surface is believed to be applied in a lot of fields, such as droplet manipulation, fluidic devices and selective catalysis.     

Characterizing the surface quality and droplet interface shape for microarray plates

The variation in the surface quality of microarray plates was examined by measuring the contact angles of 480 droplets on five microarray plates. It was found that the measured contact angle did not accurately predict the droplet shape for moderate Bond numbers (~0.5 ≤ N(B) ≤ 5). By defining an apparent contact angle using the ratio of the contact radius to the height, the variance in the predicted interface shape decreased by greater than a factor of 3 for both local and globally averaged characteristics. The error in the predicted droplet height was also reduced by 3 orders of magnitude.     

Ratchetlike slip angle anisotropy on printed superhydrophobic surfaces

The fabrication and properties of superhydrophobic surfaces that exhibit ratchet-like anisotropic slip angle behavior is described. The surface is composed of arrays of poly(dimethylsiloxane) (PDMS) posts fabricated by a type of 3D printing. By controlling the dispense parameters, regular arrays of asymmetric posts were deposited such that the slope of the posts was varied from 0 to 50 relative to the surface normal. Advancing and receding contact angles as well as slip angles were measured as a function of the post slope and droplet volume. Ratchetlike slip angle anisotropy was observed on surfaces composed of sloped features. The maximum slip angle difference (for a 180° tilt angle variation) was 32° for 20 μL droplets on surfaces with posts fabricated with a slope of 50°. This slip angle anisotropy is attributed to an increase in the triple contact line (TCL) length as the droplet is tilted in a direction against the post slope whereas the TCL decreases continuously when the drop travels in a direction parallel to the post slope. The increasing length of the TCL creates an increased energy barrier that accounts for the higher slip angles in this direction.     

可粘贴超疏水薄膜的制备

通过聚二甲基硅氧烷(PDMS)与碳纤维织物复合, 采用模板法在PDMS聚合物表面构筑微阵列结构, 制备了一种具有可重复粘贴性的超疏水薄膜. 研究结果表明, 该薄膜微结构表面的接触角为154°, 滚动角为14°, 具有低黏附的超疏水特性. 而PDMS与碳纤维织物的紧密结合, 赋予了超疏水薄膜较高的黏接力和力学性能, 断裂强度达到116.96 MPa. 所制备的超疏水薄膜可粘贴于多种材料表面, 同时经过30 d的长时间粘贴以及50次的循环粘贴后, 该薄膜依然保持着较高的黏附性能及超疏水特征, 表明超疏水薄膜具有良好的力学稳定性及耐久性, 满足长时间可重复使用的要求, 可应用于对破损超疏水涂层的快速、 大面积粘贴修复.     

Mechanical model for anisotropic curved interfaces with applications to surfactant-laden liquid-liquid crystal interfaces

A mechanical model for anisotropic curved interfaces, applicable to thermodynamically closed surfactant-laden liquid-liquid crystal interfaces is developed. The model takes into account the mechanical effects due to surface bending and surface tilting (anchoring) and incorporates liquid crystal anisotropy into classical fluid membrane mechanics. In the absence of the aligned liquid crystal, the model converges to the fluid membrane mechanical model, and in the absence of surfactant, it converges to the nematic interface mechanical model. Use of the well-known Helfrich-Rapini-Papoular surface energies leads to the Laplace equation for anisotropic curved interfaces, whose material limits are the vesicle shape equation and the liquid crystal Herring equation. Applications of the model to shape selection in liquid drops embedded in aligned nematic liquid crystals illustrates the competition between anchoring and bending and shows how anisotropic surface tension distorts the droplet and how bending tends to restore the spherical shape. This theory presented in this article shows that the interaction of interfacial anchoring and bending creates new regimes in classical fluid membrane mechanics.     

Elasticity-driven droplet movement on a microbeam with gradient stiffness: a biomimetic self-propelling mechanism

Directional movement of liquid droplets is of significance not only for certain physiological processes in nature but also for design of some microfluidic devices. In this study, we report a novel way to drive directional movement of liquid droplets on a microbeam with a varying or gradient stiffness. We use the energy method to theoretically analyze the interaction between a droplet and the elastic microbeam. The system tends to have the minimum potential energy when the droplet moves to the softer end of the beam. Therefore, a gradient change of the bending stiffness may be utilized to help the directional motion of droplets. Similarly, one can also drive droplets to move in a designed direction by varying the cross sectional geometry of the beam. Finally, some possible applications of this self-propelling mechanism are suggested.     

Lupane-type pentacyclic triterpenes in Langmuir monolayers: a synchrotron radiation scattering study

Lupane-type pentacyclic triterpenes (lupeol, betulin, and betulinic acid) are natural products isolated from various plant sources. The terpenes exhibit a vast spectrum of biological activity and are applied in therapies for different diseases, among which the anticancer, anti-HIV, antihypercholesteremic, and antiinflammatory are the most promising. These chemicals possess amphiphilic structure and were proved to interact strongly with biomembranes, which can be the key stage in their mechanism of action. In our studies, we applied Langmuir monolayers as versatile models of biomembranes. It turned out that the three investigated terpenes are capable of stable monolayer formation; however, these monolayers differ profoundly regarding their physicochemical characteristics. In our research, we applied the Langmuir technique (surface pressure-mean molecular area (π-A) isotherm registration) coupled with Brewster angle microscopy (BAM), but the main focus was on the synchrotron radiation scattering method, grazing incidence X-ray diffraction (GIXD), which provides information on the amphiphilic molecule ordering in the angstr?m scale. It was proved that all the investigated terpenes form crystalline phases in their monolayers. In the case of lupeol, only the closely packed upright phase was observed, whereas for betulin and betulinic acid, the phase situation was more complex. Betulinic acid molecules can be organized in an upright phase, which is crystalline, and in a tilted phase, which is amorphous. The betulin film is a conglomerate of an upright crystalline monolayer phase, tilted amorphous monolayer phase, and a crystalline tilted bilayer. In our paper, we discuss the factors leading to the formation of the observed phases and the implications of our results to the therapeutic applications of the native lupane-type triterpenes.