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Comment Heat Transfer

Self-healing hydrophobic coatings enhance heat transfer in steam condensers

By Scott Jenkins |

Ultrathin (less than 100 nm) hydrophobic coatings on alloys and other engineering materials could enhance heat and mass transfer in a range of processing applications, but achieving lasting durability for such thin coatings in real-world settings has been a major ongoing challenge. Now, researchers at the University of Illinois (Champaign, Ill.; www.illinois.edu) have developed a coating material that can repair itself after scratching, cutting and other damage, extending its durability even at nanoscale thicknesses.

The current research project, led by University of Illinois engineering professor Nenad Miljkovic and published in Nature Communications, focused on using the coatings to boost the efficiency of condensers in power-plant steam systems. Hydrophobic coatings render the metals more water-resistant and efficient at forming water droplets, which enhances heat transfer, the team notes. In steam power plants, thin coatings can break down quickly. Thicker coatings can be more durable, but they reduce heat transfer and erode the associated benefit of the coating.

To avoid this tradeoff, the researchers designed and synthesized a vitrimer thin film with polydimethylsiloxane network strands and dynamic boronic ester crosslinks. Named dyn-PDMS, the coating material takes advantage of the inherent hydrophobic nature of silicones, and provides a mechanism for self-healing, due to the dynamic exchange of bonds in their network strands, the researchers say. Vitrimers refer to a class of materials with covalent bond networks that can undergo bond exchange.

The film “maintains excellent hydrophobicity and optical transparency after scratching, cutting, and indenting,” the researchers say. In addition to enhanced heat transfer, the coating material could have a range of other potential applications, such as self-cleaning, anti-icing, anti-fogging, anti-bacterial or anti-fouling coatings.

The dyn-PDMS can be easily dip-coated onto surfaces — including silicon, aluminum, copper and steel — in nanoscale layers.

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