Researchers at Rice University have addressed a long-standing limitation of superhydrophobic, or “never-wet,” surfaces by developing a low-cost, scalable coating that continues to repel hot water droplets even as they approach boiling temperatures. Conventional superhydrophobic materials rely on micro- and nanoscale textures that trap air, letting water bead up and roll off. This mechanism fails when liquids exceed roughly 40°C because evaporation and recondensation fill those textures with liquid, creating sticky bridges that cause droplets to cling and leave residue.
The Rice team’s solution adds a thin thermally insulating layer beneath a commercially available superhydrophobic spray coating. This multilayered insulated superhydrophobic (MISH) design reduces heat transfer from the droplet to the surface, limiting evaporation and condensation within the surface microstructure. The result: hot droplets up to about 90°C continue to slide off rather than stick, a significant improvement over traditional coatings.
In laboratory tests, the insulated coatings outperformed standard versions across a range of challenges. When tilted samples were exposed to heated droplets, the MISH surfaces showed far less adhesion at elevated temperatures. A theoretical heat-transfer model confirmed that insulation alone could predictably tune repellency without altering surface chemistry or texture. In hot jet and long-duration droplet-impact tests, the insulated coatings sustained repellency far longer than conventional materials.
To evaluate real-world potential, the researchers tested the coatings with hot liquids such as coffee, milk, and soup on larger and curved surfaces. Less than 1% of these fluids remained on MISH-treated surfaces compared with about 31% on typical superhydrophobic coatings.
Because MISH uses readily available materials and simple application methods, it presents a practical, economical path for industries that handle warm or hot fluids. Future work will focus on enhancing long-term durability, particularly the stability of the outer coating layer.