水最可怕的噩梦：超疏水材料的兴起

诸平

Fig. 1 Research on metal-organic frameworks has led to the development of superhydrophobic surfaces by grafting hydrocarbon chains, which create a high-entropy state essential for minimizing water adhesion. (Artist’s concept.) Credit: SciTechDaily.com

Fig. 2 Left: Porous substrate with a small water contact angle: The surface absorbs a lot of liquid. Right: The new material features a large water contact angle and is thus nearly completely hydrophobic. Credit: KIT

据德国卡尔斯鲁厄理工学院（Karlsruhe Institute of Technology简称KIT）2024年12月28日提供的消息，水最可怕的噩梦：超疏水材料的兴起（Water’s Worst Nightmare: The Rise of Superhydrophobic Materials）。具有近乎完美防水性的新材料为汽车和建筑物的自清洁表面提供了潜力。

来自德国卡尔斯鲁厄理工学院（KIT）和印度古瓦哈蒂理工学院{Indian Institute of Technology Guwahati (IITG), Assam, India}的科学家们，已经开发出一种几乎完全排斥水滴的表面材料。他们采用一种完全创新的工艺，通过接枝碳氢链，将人工设计的金属有机框架（Metal-organic frameworks简称MOF）材料具有了新的性能。由此产生的超疏水{superhydrophobic (extremely water-repellent) properties}特性，对于作为需要抵御环境影响的自清洁表面（如汽车或建筑物）来说是很有趣的。这项研究于2024年11月15日已经在《材料视野》（Materials Horizons）杂志网站发表（印刷版将在2025年出版）——Evgenia Bogdanova, Modan Liu, Patrick Hodapp, Angana Borbora, Wolfgang Wenzel, Stefan Bräse, André Jung, Zheqin Dong, Pavel A. Levkin, Uttam Manna, Tawheed Hashem, Christof Wöll. Functionalization of monolithic MOF thin films with hydrocarbon chains to achieve superhydrophobic surfaces with tunable water adhesion strength. Materials Horizons, 2025. DOI: 10.1039/D4MH00899E. First published: Epub 15 November 2024. https://pubs.rsc.org/en-us/content/articlelanding/2025/mh/d4mh00899e

MOF的超疏水表面（Superhydrophobic Surfaces from MOFs）

金属有机骨架（MOFs）是由金属离子通过有机连接剂连接而成，形成多孔的海绵状结构。它们惊人的表面积（只有2 g，就可以覆盖一个足球场大小的面积），这使得它们在气体储存、二氧化碳分离和先进的医疗技术等应用中很有价值。

除了内部孔隙，MOFs的外表面也具有独特的性能。研究人员通过将碳氢化合物链接枝到MOF薄膜上来增强这些表面，从而制造出一种接触角超过160度的防水材料。更高的接触角意味着更好的疏水性，因为水滴形成接近球形而不是散开。

KIT功能界面研究所{Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), Hermann-von-Helmholtz Platz-1, 76344 Eggenstein-Leopoldshafen, Germany}的克里斯托夫·沃尔教授（Professor Christof Wöll）解释说：“通过我们的方法，我们能够获得接触角明显高于其他光滑表面和涂层的超疏水表面。虽然MOF粉末颗粒的润湿特性之前已经被探索过，但将单片MOF薄膜用于这一目的是一个开创性的概念。”

下一代“超疏水”材料（Next-Generation “Superhydrophobic” Materials）

研究小组将这些结果归因于MOFs上碳氢化合物链的刷状排列（聚合物刷）。在被接枝到MOF材料上后，它们倾向于形成一种无序状态，科学家称之为高熵状态（“high-entropy state”），这对其疏水性至关重要。科学家们断言，这种接枝碳氢化合物链的状态在其他材料上是观察不到的。

值得注意的是，即使用全氟烃链接枝，即用氟取代氢原子，水接触角也没有增加。在聚四氟乙烯（Teflon）等材料中，全氟化会带来超疏水性。然而，正如研究小组发现的那样，在新开发的材料中，它显著降低了水的接触角。计算机模拟的进一步分析证实，与碳氢化合物链相反，全氟化分子不可能处于能量有利的高熵态。

从表面粗糙度和理论分析的见解（Insights from Surface Roughness and Theoretical Analysis）

此外，科学家们在纳米范围内改变了SAM@SURMOF系统的表面粗糙度，从而进一步降低了水的粘附强度。即使倾角非常小，水滴也开始滚出，其疏水性和自清洁性能显著提高。

IITG化学系{Indian Institute of Technology Guwahati (IITG), Department of Chemistry, Assam, India}的乌塔姆·曼纳教授（Professor Uttam Manna）说：“我们的工作还包括详细的理论分析，将实验中显示的意外行为与接枝到MOF薄膜上的分子的高熵状态联系起来。这项研究将改变具有最佳疏水性的下一代材料的设计和生产。”

上述介绍，仅供参考。欲了解更多信息，敬请注意浏览原文或者相关报道。

Abstract

While the accessible pores render an enormous variety of functionalities to the bulk of metal–organic frameworks (MOFs), the outer surfaces exposed by these crystalline materials also offer unique characteristics not available when using conventional substrates. By grafting hydrocarbon chains to well-defined MOF thin films (SURMOFs) prepared using layer-by-layer methods, we were able to fabricate superhydrophobic substrates with static water contact angles over 160°. A detailed theoretical modelling of the hydrocarbon chains grafted on the outer SURMOF surface with well-defined spacing between anchoring points reveals that the grafted hydrocarbon chains behave similarly to polymer brushes during wetting, where conformational entropy is traded with mixing entropy. The chains are coiled and can access many different conformations, as evidenced directly by infrared spectroscopy. The entropic contributions from the coiled state lead to a pronounced reduction of the surface free energy, rendering superhydrophobic properties to the functionalized SURMOFs. On the other side, the water adhesion strength could be decreased by increasing the surface roughness on the nanometer scale.

New concepts

Our paper introduces an innovative and unique approach for creating superhydrophobic surfaces using MOF thin films. This technique employs porous coatings, a fresh idea for achieving hydrophobicity. Although the wetting properties of MOF powder particles have been explored, applying monolithic MOF thin films for this purpose is a groundbreaking concept. Our method produces superhydrophobic surfaces with contact angles significantly higher than those of other coatings with similar roughness. Moreover, we can adjust the water adhesion strength across a wide range.