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The Development of Materials That Are Superhydrophobic
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Posted by Okachinepa on 12/28/2024 @
Courtesy of SynEvol
Credit: Karlsruhe Institute of Technology
Metal-organic frameworks (MOFs) are porous structures composed of metal ions joined by organic linkers. They are useful for gas storage, carbon dioxide separation, and cutting-edge medical technology because of their extraordinary surface area—two grams can cover the area of a football field.
In addition to their internal pores, MOFs' external surfaces have special qualities. By grafting hydrocarbon chains onto thin MOF films, researchers improved these surfaces and produced a water-repellent substance with a contact angle greater than 160 degrees. Better hydrophobicity results from a higher contact angle because water droplets take on a roughly spherical shape rather than dispersing.
Professor Christof Wöll of KIT's Institute of Functional Interfaces explains, "We are able to achieve superhydrophobic surfaces with contact angles that are significantly higher than those of other smooth surfaces and coatings." "The use of monolithic MOF thin films for this purpose is a groundbreaking concept, even though the wetting properties of MOF powder particles have been investigated previously."
Courtesy of Synevol
Credit KIT
The group ascribes these findings to the hydrocarbon chains' brush-like configuration (polymer brushes) on the MOFs. Its hydrophobic qualities depend on their tendency to form "coils" after being grafted onto MOF materials, a disorderly state known to scientists as the "high-entropy state." The researchers claimed that other materials were unable to exhibit this condition of the grafted hydrocarbon chains.
It is noteworthy that even when they employed perfluorinated hydrocarbon chains for grafting—that is, replacing hydrogen atoms with fluorine—the water contact angle remained constant. Perfluorination gives compounds like Teflon their superhydrophobic qualities. However, the scientists discovered that the newly created material drastically reduced the water contact angle. Additional computer simulation analyses verified that unlike hydrocarbon chains, the perfluorinated molecules were unable to adopt the high-entropy state, which is energetically advantageous.
To further lessen the water adhesion strength, the researchers also adjusted the surface roughness of their SAM@SURMOF devices in the nanoscale range. Their hydrophobic and self-cleaning qualities were greatly enhanced, and water droplets began to roll off even at very low inclination angles.
Professor Uttam Manna of IITG's Chemistry department adds, "Our work also includes a detailed theoretical analysis that links the unexpected behavior shown in experiments to the high-entropy state of the molecules grafted to the MOF films." "The design and manufacturing of next-generation materials with optimal hydrophobic properties will be altered by this study."
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