Innovative Materials Repel Water Almost Completely
Researchers from the Karlsruhe Institute of Technology (KIT) from Helmholtz Information and the Indian Institute of Technology Guwahati (IITG) have developed a surface material that almost completely repels water. Using a novel approach, they modified metal-organic frameworks (MOFs) — artificially designed materials with unique properties — by incorporating hydrocarbon chains. The resulting superhydrophobic, highly water-repellent surfaces are promising for applications requiring environmental resilience, such as in automotive design or architectural structures. The study was published in the journal Materials Horizons. (Source: Karlsruhe Institute of Technology – Press Releases)
MOFs (short for Metal-Organic Frameworks) are composed of metal atoms connected by organic molecular linkers, forming porous networks similar to sponges. Their volumetric properties are remarkable — two grams of the material, if fully unfolded, would cover the area of a football field. These characteristics make MOFs highly suitable for applications such as gas storage, carbon dioxide capture, and emerging technologies in the medical field.
However, the external surfaces of these crystalline materials also offer unique opportunities, which the research team exploited with a novel idea: They anchored hydrocarbon chains onto thin MOF films. This achieved a water contact angle of more than 160 degrees — the larger the angle formed by a water droplet on a surface, the more water-repellent the material becomes. “Our method creates superhydrophobic surfaces with contact angles significantly higher than those of other smooth surfaces and coatings,” explains Professor Christof Wöll from the Institute of Functional Interfaces at KIT. “While the wettability of MOF powder particles has been studied before, using homogeneous MOF thin films for this purpose is a groundbreaking concept.”
Next Generation of Superhydrophobic Materials
The team attributes these results to the brush-like arrangement (polymer brushes) of hydrocarbon chains on the MOFs. After being anchored to the MOF material, these chains can form “coils” — a state of disorder known in science as a “high-entropy state” — which is essential for the material’s water-repellent properties. According to the researchers, such behavior has not been observed for hydrocarbon chains anchored to other materials.
Remarkably, the water contact angle did not increase through fluorination of the hydrocarbon chains — the replacement of hydrogen atoms with fluorine. In materials like Teflon, fluorination leads to highly water-repellent surfaces. However, with the newly developed material, fluorination even significantly reduced the water contact angle. Further computer simulations confirmed that perfluorinated molecules, unlike hydrocarbon chains, cannot assume the energetically favorable high-entropy state.
Additionally, the research team adjusted the surface roughness of their SAM@SURMOF systems on the nanometer scale. This further reduced adhesion, allowing water droplets to roll off at extremely small tilt angles, enhancing the material’s water-repellent and self-cleaning properties.
“Our work also provides a comprehensive theoretical analysis linking unexpected experimental behaviors to the high-entropy state of molecules attached to MOF films,” says Professor Uttam Manna from the Department of Chemistry at IITG. “This study will transform the design and production of the next generation of materials with optimal hydrophobic properties.”
KIT/C. Könemann, 12.12.2024
Note: The article has been translated from German to English. It is based on a press release from KIT.
The original press release can be found at:
Neuartige Materialien weisen Wasser nahezu vollständig ab (only in german)
The original publication can be found at:
Evgenia Bogdanova, Modan Liu, Patrick Hodapp, Angana Borbora, Wolfgang Wenzel, Stefan Bräse, André Jung, Zheqin Dong, Pavel Levkin, Uttam Manna, Tawheed Hashem und Christof Wöll: Functionalization of Monolithic MOF Thin Films with Hydrocarbon Chains to Achieve Superhydrophobic Surfaces with Tunable Water Adhesion Strength, Royal Society of Chemistry, Materials Horizons 2024, DOI: 10.1039/D4MH00899E
Localization in Helmholtz Information:
Helmholtz Information, Program 3: Materials Systems Engineering, Topic 3: Adaptive and Bioinstructive Materials Systems
Contact:
Prof. Dr. Christof Wöll
Director Institute of Functional Interfaces (IFG)
Karlsruhe Institute of Technology (KIT)
Phone: +49 721-608-2-3934
E-Mail: christof.woell@kit.edu
Contact for this press release:
Christian Könemann
Press Officer
Karlsruhe Institute of Technology (KIT)
Phone: +49 721-608-41105
E-Mail: christian.koenemann@kit.edu
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