不同粒子构建的液体弹珠的研究进展

液体弹珠是粒子包裹液体形成的不粘湿液滴。由于液体弹珠表面粒子阻止了内部液滴与外部基底的直接接触,使其能在固体和液体表面稳定存在,显示出独特的性能,在微反应器、传感器、生物医药和微流控等领域有着潜在的应用价值。液体弹珠的壳层粒子来源丰富,且不同粒子构筑的液体弹珠具有不同的性能和应用领域。本文综述了二氧化硅(SiO₂)、四氧化三铁(Fe₃O₄)、石松、聚四氟乙烯(PTFE)和纤维素等壳层粒子衍生出的液体弹珠,并展望了液体弹珠的发展趋势和应用前景。     

聚(环三磷腈-co-4,4'-(9-芴)二苯酚)微球的制备及其稳定液体弹珠的性能研究

以六氯环三磷腈和4,4'-(9-芴)二苯酚为共聚单体,三乙胺为缚酸剂,乙腈为溶剂,通过一步沉淀聚合制备了疏水性的交联聚(环三磷腈-co-4,4'-(9-芴)二苯酚)(PZHF)微球,通过傅立叶变换红外光谱仪(FTIR)、X射线光电子能谱仪(XPS)和扫描电子显微镜(SEM)对微球的化学结构和形貌进行了表征;进一步以该微球为稳定剂,通过包覆水滴成功制备了液体弹珠,研究了液体弹珠的静态稳定性以及共聚物微球在液体弹珠表面的分布情况,并考察了液体弹珠的气体透过性.结果表明,PZHF微球具有高度交联的有机-无机杂化结构,平均粒径为1.3μm,且微球表面较为粗糙,具有疏水性;用其包覆水滴可得到稳定的液体弹珠,微球在气-液界面上的排列较为疏松,使液体弹珠具有独特的气体透过性,外界气体可通过液体弹珠表面进入内部水相而不破坏弹珠自身的结构.     

基于液体弹珠原位制备载水胶囊及其性能

首先以疏水性二氧化硅微粒为稳定剂,通过包覆水滴制备了液体弹珠;然后在其表面滴涂α-氰基丙烯酸乙酯,通过湿气固化制得聚合物涂层封装的液体弹珠;最后在弹珠表面进一步涂覆环氧大豆油丙烯酸酯涂层,通过紫外光固化制得载水胶囊。采用数码照片、超景深显微镜、扫描电子显微镜对液体弹珠及载水胶囊的形貌进行了表征;采用实时傅里叶红外光谱研究了光固化涂层的双键转化率,探讨了涂层的硬度、耐水性等基本性质;并研究了载水胶囊的力学强度及保水性能。结果表明:相较于原始液体弹珠,所制备的载水胶囊表面光滑且致密;由聚α-氰基丙烯酸乙酯涂层和环氧大豆油丙烯酸酯光固化涂层组成的壁材赋予了载水胶囊良好的水汽阻隔性能和力学性能。     

液体橡皮泥:属性特征、制备策略及应用探索

液体橡皮泥是指空气环境中被颗粒包裹的以可塑性和复杂形状为特征的液体系统,目前已被成功应用于气体传感、蛋白质分析、光催化等领域,并展现出了很多独特优势。这是一种新兴的软物质体系,与被颗粒包裹的形状为类球形的液体弹珠组成相似,但打破了后者的形状单一性。本文从裸液滴和液体弹珠出发,通过对液体形状和颗粒堵塞问题的分析,梳理了液体橡皮泥技术的建立过程。随后,论述了国内外的研究进展,对不同种类液体橡皮泥的制备、特性及应用进行了概括和分析,重点讨论了单层纳米颗粒结构液体橡皮泥的系列研究。最后,围绕液体橡皮泥的概念内涵、制备方法、特性对比、功能应用等问题进行了总结和探讨,并就未来发展方向和研究思路提出了建议。     

微液滴的非机械驱动

微液滴的非机械驱动是操纵微小尺雨液体流动的新方法。本文介绍当前有关微液滴非机械驱动的研究进展，包括：利用电化学方法产生并消耗表面活性分子来产生表面张力梯度；把表面浸润性梯度和温度梯度相结合；通过光敏化合物偶氮部分顺反异构的转换导致表面自由能的变化，最后由光照来驱动微液滴，以及利用固体基片上的亲水疏水条纹构建微芯片上实验室的液体非机械输送网络。     

纳米结构表面浸润性质的分子动力学研究

采用分子动力学方法研究了氩纳米液滴在铂金属及其模型固体表面的浸润现象,获得了液滴在平滑表面和三角纳米结构阵列表面的接触角和展布特性.研究表明,液滴与壁面的势能作用较强时,液滴与纳米结构表面为均匀浸润,但是由于迟滞效应,接触角受表面纳米结构的影响不明显;势能作用较弱时,纳米结构间隙中存在类似蒸汽的低密度相,液滴与纳米结构表面为非均匀浸润,接触角受纳米结构的影响而增大;表面纳米结构可以使表面具有超疏水性.     

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。     

仿生超疏水表面的抗冷凝失效研究进展

在存在一定过冷度或蒸汽过饱和度的条件下,水蒸汽可在固体表面凝结成核.随着过冷度增大,液滴成核半径将随之减小,冷凝液滴的生长融合将无法避免地发生在超疏水表面不可或缺的微/纳米结构内.若液滴不能及时排出,则会滞留在表面结构内并挤出空气,形成局部浸润,导致材料表面的超疏水性能下降或失效,甚至引起泛洪.本文首先总结了表面因冷凝...     

各向异性浸润表面在液体操控中的应用

在自然界中,各种生物表面,如水稻叶、蝴蝶翅膀、沙漠甲虫鞘翅、蜘蛛丝、仙人掌刺及猪笼草口缘等,都存在着各向异性浸润性.当液体接触线遇到固体表面的物理不对称性或化学不均匀性时,就会发生各向异性浸润现象,表现为表面在特定而非随机的方向上展现出不同的液滴接触角和滑动角,并伴随着液体的各向异性扩散和各向异性运动行为.近年来,各向异性浸润表面的理论研究和实际应用引起了人们广泛的关注.液体操控,尤其是可控定向液体输送,作为一种极具发展前景的重要智能液体操纵形式,在许多领域发挥着重要作用.各向异性浸润表面因其独特的物理化学性质,在液体操控领域的应用获得了快速发展.本文结合本课题组的研究工作,提出了各向同性浸润和各向异性浸润的有关观点,总结了以微/纳米结构为主的人造各向异性浸润表面在液体操控领域的最新进展,包括可控浸润性、微流控及液体运输和水/雾收集.最后讨论了这一快速发展领域目前面临的挑战和未来的发展前景.     

微流体技术制备聚合物微粒的研究进展 Ⅰ.合成聚合物颗粒的方法及颗粒种类

综述了微流体技术合成聚合物颗粒的研究进展,包括基于液滴的合成、用流动刻蚀的技术合成及在设备中交替组装成复杂颗粒等合成组装技术,介绍了由此合成的一些不同形状和结构的颗粒及其性能,其中包括具备低密度和特殊表面性能的多孔性颗粒、可以通过加入功能物质制备出的性能优异的复合颗粒、拥有层状结构及多重性能的多功能颗粒、基础的球形颗粒以及通过微流体设备制备的非球形颗粒。     

Formation of liquid marbles and wetting transitions

The formation of liquid marbles was studied in the situation where hydrophobic particles coating the marbles "come from air". Droplets of water/ethanol solutions of various concentrations were coated with three kinds of powders: polytetrafluoroethylene, polyvinylidene fluoride and polyethylene. We established that there exists a critical concentration of ethanol, and correspondingly a critical surface tension of the water/ethanol solution allowing formation of liquid marbles. A critical surface tension depends on the kind of the powder. In parallel, wetting transitions of water/ethanol solutions were studied on the layers of the same polymer powders. The onset of wetting transitions on the powders took place at the concentrations of ethanol coinciding with those enabling the formation of liquid marbles. Wetting transitions stipulate the formation of liquid marbles when a droplet is deposited on a layer of hydrophobic powder. This assumption was validated by the experiments performed with di-iodomethane and glycerol.     

Freezing of a liquid marble

In this study, we present for the first time the observations of a freezing liquid marble. In the experiment, liquid marbles are gently placed on the cold side of a thermo-electric cooler (TEC), and the morphological changes are recorded and characterized thereafter. These liquid marbles are noticed to undergo a shape transition from a spherical to a flying-saucer-shaped morphology. The freezing dynamics of liquid marbles is observed to be very different from that of a freezing water droplet on a superhydrophobic surface. For example, the pointy tip appearing on a frozen water drop could not be observed for a frozen liquid marble. In the end, we highlight a possible explanation of the observed morphology.     

Silica‐Based Liquid Marbles as Microreactors for the Silver Mirror Reaction

Little attention has been paid to the participation of the shell of silica‐particle‐based liquid marbles and their influence on chemical reactions. The fabrication of liquid marbles with the encapsulating particle shells not only act as protecting layers to provide a confined environment, but also provide the reactive substrate surfaces to regulate the classical silver mirror reaction. Fabrication of silver mirrors with different morphologies was achieved by modifying particle surface properties, which could further lead to Janus liquid marbles. The different evaporation behavior of microreactors was demonstrated. Micrometer‐sized silica particles were used for the preparation of monolayer‐stabilized liquid marbles, which show great potential in fabricating Janus particles from superhydrophobic particles that are not attainable from Pickering emulsions.     

Liquid marbles prepared from pH-responsive sterically stabilized latex particles

Submicrometer-sized pH-responsive sterically stabilized polystyrene (PS) latex particles were synthesized by dispersion polymerization in isopropyl alcohol with a poly[2-(diethylamino)ethyl methacrylate]- (PDEA-) based macroinitiator. These PDEA-PS latexes were extensively characterized with respect to their particle size distribution, morphology, chemical composition, and pH-responsive behavior. Millimeter- and centimeter-sized "liquid marbles" with aqueous volumes varying between 15 μL and 2.0 mL were readily prepared by rolling water droplets on the dried PDEA-PS latex powder. The larger liquid marbles adopted nonspherical shapes due to gravitational forces; analysis of this deformation enabled the surface tension to be estimated. Scanning electron microscopy and fluorescence microscopy studies indicated that flocs of the PDEA-PS particles were adsorbed at the surface of these water droplets, leading to stable liquid marbles. The relative mechanical integrity of the liquid marbles prepared from alkaline aqueous solution (pH 10) was higher than those prepared from acidic aqueous solution (pH 2) as judged by droplet roller experiments. These liquid marbles exhibited long-term stability (over 1 h) when transferred onto the surface of liquid water, provided that the solution pH of the subphase was above pH 8. In contrast, the use of acidic solutions led to immediate disintegration of these liquid marbles within 10 min, with dispersal of the PDEA-PS latex particles in the aqueous solution. Thus the critical minimum solution pH required for long-term liquid marble stability correlates closely with the known pK(a) value of 7.3 for the PDEA stabilizer chains. Stable liquid marbles were also successfully prepared from aqueous Gellan gum solution and glycerol.     

Janus droplets: liquid marbles coated with dielectric/semiconductor particles

The manufacturing of water droplets wrapped with two different powders, carbon black (semiconductor) and polytetrafluoroethylene (dielectric), is presented. Droplets composed of two hemispheres (Janus droplets) characterized by various physical and chemical properties are reported first. Watermelon-like striped liquid marbles are reported. Janus droplets remained stable on solid and liquid supports and could be activated with an electric field.     

Measurement of the surface tension of liquid marbles

The capillary rise and Wilhelmy plate methods have been used to study the "surface tension" of water marbles encapsulated with polytetrafluoroethylene (PTFE) powders of 1-, 35-, and 100-μm particle size. With the capillary rise technique, a glass capillary tube was inserted into a water marble to measure the capillary rise of the water. The Laplace pressure exerted by the water marble was directly measured by comparing the heights of the capillary rise from the marble and from a flat water surface in a beaker. An equation based on Marmur's model was proposed to calculate the water marble surface tension. This method does not require the water contact angle with the supporting solid surface to be considered; it is therefore a simple but efficient method for determining liquid marble surface tension. The Wilhelmy method was used to measure the surface tension of a flat water surface covered by PTFE powder. This method offers a new angle for investigating liquid marble shell properties. A discussion on the nature and the realistic magnitude of liquid marble surface tension is offered.     

Plasmonic Liquid Marbles: A Miniature Substrate‐less SERS Platform for Quantitative and Multiplex Ultratrace Molecular Detection

Inspired by aphids, liquid marbles have been studied extensively and have found application as isolated microreactors, as micropumps, and in sensing. However, current liquid‐marble‐based sensing methodologies are limited to qualitative colorimetry‐based detection. Herein we describe the fabrication of a plasmonic liquid marble as a substrate‐less analytical platform which, when coupled with ultrasensitive SERS, enables simultaneous multiplex quantification and the identification of ultratrace analytes across separate phases. Our plasmonic liquid marble demonstrates excellent mechanical stability and is suitable for the quantitative examination of ultratrace analytes, with detection limits as low as 0.3 fmol, which corresponds to an analytical enhancement factor of 5×10⁸. The results of our simultaneous detection scheme based on plasmonic liquid marbles and an aqueous–solid–organic interface quantitatively tally with those found for the individual detection of methylene blue and coumarin.     

Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble’s surface temperature between 21–135 °C and its encapsulated water temperature between 21–74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12‐fold superior reaction rate constant for methylene blue degradation than at room temperature.     

Spheroid cultivation of HT-29 carcinoma cell line in liquid marbles

The ability to simulate the 3D structure of a human body is essential to increase the efficiency of drug development. In vivo conditions are significantly different in comparison to in vitro conditions. A standardly used cell monolayer on tissue culture plastic (2D cell culture) is not sufficient to simulate the transfer phenomena occurring in living organisms, therefore, cell growth in a 3D space is desired. Drug absorption, distribution, metabolism, excretion and toxicity could be tested on 3D cell aggregates called spheroids, decrease the use of animal models and accelerate the drug development. In this work, the formation of spheroids from HT-29 human colorectal adenocarcinoma cells was successfully achieved by means of the so-called liquid marbles, which are liquid droplets encapsulated by a hydrophobic powder. During the cultivation in the medium inside the liquid marbles, cells spontaneously formed spherical agglomerates (spheroids) without the need of any supporting scaffold. The study focused on the influence of different parameters—namely liquid marble volume, seeding cell density and time of cultivation—on the final yield and quality of spheroids. This work has shown that using liquid marbles as microbioreactors is a suitable method for the cultivation of HT-29 cells in the form of spheroids.     

Liquid Marbles Based on Magnetic Upconversion Nanoparticles as Magnetically and Optically Responsive Miniature Reactors for Photocatalysis and Photodynamic Therapy

Magnetic liquid marbles have recently attracted extensive attention for various potential applications. However, conventional liquid marbles based on iron oxide nanoparticles are opaque and inadequate for photo‐related applications. Herein, we report the first development of liquid marbles coated with magnetic lanthanide‐doped upconversion nanoparticles (UCNPs) that can convert near‐infrared light into visible light. Apart from their excellent magnetic and mechanical properties, which are attractive for repeatable tip opening and magnetically directed movements, the resultant UCNP‐based liquid marbles can act as ideal miniature reactors for photodynamic therapy of cancer cells. This work opens new ways for the development of liquid marbles, and shows great promise for liquid marbles based on UCNPs to be used in a large variety of potential applications, such as photodynamic therapy for accelerated drug screening, magnetically guided controlled drug delivery and release, and multifunctional actuation.