Superhydrophobic surfaces, long celebrated for their remarkable water-repellent properties, have revolutionized numerous applications by enabling water droplets to bead up and swiftly roll off. This quintessential “never-wet” behavior has empowered advances ranging from self-cleaning materials to anti-corrosive coatings. However, these surfaces harbor a critical vulnerability: their performance dramatically deteriorates in the presence of hot water. When liquid temperatures exceed approximately 40 degrees Celsius, traditional superhydrophobic coatings lose their effectiveness with an alarming abruptness. Instead of repelling, hot droplets become sticky, seeping into the micro- and nanoscale structures that confer their superhydrophobic nature, thereby leaving damp patches and unsightly residue behind.
Addressing this longstanding challenge, researchers at Rice University, under the guidance of assistant professor of mechanical engineering Daniel J. Preston, have unveiled a novel approach that sidesteps conventional wisdom. Rather than solely engineering the surface chemistry or texture, their breakthrough centers on manipulating heat transfer within the surface itself. By integrating a thin, thermally insulating layer beneath a widely available superhydrophobic spray coating, they have devised a multilayered insulated superhydrophobic (MISH) surface capable of repelling hot water droplets even as their temperatures near boiling—up to an unprecedented 90 degrees Celsius. This development, detailed in their recent publication in ACS Applied Materials & Interfaces, redefines the boundaries of superhydrophobic technology, pushing it well beyond previously accepted thermal limits.
Preston emphasizes the practicality and economic advantage of their method, noting that earlier high-performance hot-water-repellent coatings required sophisticated cleanroom nanofabrication steps and costs exponentially greater than their streamlined system. “Our MISH coating performs robustly in real-world conditions across various geometries—from curved pipes to industrial bowls—demonstrating scalability and ease of application,” Preston attests. This contrasts starkly with traditional superhydrophobic surfaces, whose delicate trapped air pockets collapse under heat stress, causing rapid functional decline.
The science underlying this advancement involves a nuanced interplay between surface texture, temperature gradients, and phase change phenomena. Classic superhydrophobic surfaces maintain a fragile air cushion atop microscale roughness, effectively minimizing water-solid contact area and adhesion. However, when a hot water droplet contacts a cooler textured surface, water evaporates locally and then recondenses within the surface’s microcavities. This recondensation forms liquid “bridges” that replace the insulating air pockets, anchoring droplets firmly and transitioning the surface into a wetted, sticky regime. Such thermal interactions impose severe operational limitations for industries working with hot fluids, including food processing, desalination, and sterile chemical manufacturing.
Instead of attempting to engineer ever more complex surface chemistries to resist this transition, the Rice team redirected focus toward heat flow management within the coating architecture. Zhen Liu, co-lead author and recent doctoral graduate from Preston’s lab, explains, “By incorporating a thin insulation layer—commonly a sprayable polyurethane foam—we dramatically reduce heat conduction from droplet to substrate. This impairs the evaporation-condensation cycles responsible for liquid bridge formation and preserves the air cushion critical for repellency.” The topcoat remains a commercially accessible superhydrophobic spray, emphasizing the method’s compatibility with off-the-shelf materials.
The MISH system’s two-layer design thus synergizes thermal insulation with superhydrophobic microtexture to mitigate inherent thermal defects. Experimental testing involved systematically heating coated samples and challenging them with hot water droplets under gravity to evaluate sliding behavior. Compared against conventional surfaces, MISH coatings exhibited significantly reduced droplet adhesion at elevated temperatures; droplets resisted sticking and rolled off effortlessly up to near-boiling points. Such empirical results aligned well with an accompanying heat transfer model that decoupled surface chemistry effects from insulation performance, validating the theoretical framework.
Additional rigorous tests replicated industrial scenarios by subjecting coatings to continuous hot water jets. While traditional coatings rapidly failed in these conditions, MISH surfaces, particularly those with thicker insulating layers, reliably repelled water jets, indicating promising durability and robustness. To further stress the system, coatings endured nearly two million droplet impacts over the course of a week-long exposure, mirroring extreme usage cycles. Whereas standard coatings lost repellency immediately, MISH-treated surfaces maintained their functionality past one million impacts before gradual degradation occurred. Detailed analyses revealed that failure initiated within the commercial topcoat’s material properties rather than the insulating design, suggesting that future iterations employing more thermally and chemically stable top layers could greatly extend lifespan.
To verify practical applicability beyond the laboratory, the team deployed MISH coatings on larger surfaces, including curved pipes and vessels, then subjected them to real hot liquids common in food and beverage industries such as hot milk, coffee, and split pea soup. Remarkably, these trials resulted in less than 1% residual wetness on MISH surfaces versus over 30% residue on standard superhydrophobic coatings—an outcome with direct implications for reducing contamination, simplifying cleaning, and decreasing waste in commercial settings.
Preston acknowledges that while this innovation marks a significant leap forward, further research is needed to improve long-term durability, particularly at elevated temperatures and in chemically harsh environments. This future work is poised to explore advanced insulating materials, novel nanostructured top layers, and manufacturing techniques transcending simple spray coatings to create even more resilient superhydrophobic surfaces with sustained high-temperature performance. The promise of cost-effective, scalable, and broadly applicable coatings holds potential to transform how industries handle hot liquids, enhancing efficiency and environmental sustainability.
By fundamentally addressing the geothermal root of superhydrophobic failure rather than its symptoms, this approach revolutionizes the design paradigm for water-repellent materials. It exemplifies how merging fundamental thermal physics with practical engineering can unlock exponential gains in performance without prohibitive cost. Co-lead author Rawand Rasheed, a Rice alumnus and CEO of Preston’s spinout company Helix Earth, underscores this synergy: “Our findings highlight that deep scientific understanding married with real-world engineering pragmatism yields massive advancements, heralding a new era of hot-water-repellent technology.”
In summary, the MISH coating represents an exciting and scalable breakthrough in surface science. Its combination of thermal insulation and microtextured superhydrophobicity defies previous thermal constraints, allowing surfaces to maintain their coveted water-repelling properties even near boiling temperatures. As future research hones durability and expands applications, this technology is poised to catalyze significant improvements in industries reliant on hot liquids. By preventing hot water from sticking and fouling surfaces, MISH coatings pave the way for cleaner, more efficient, and less wasteful industrial processes worldwide.
Subject of Research: Mechanical engineering, Superhydrophobic surfaces, Thermal insulation
Article Title: Scalable Hot-Water-Repellent Superhydrophobicity via Thermal Insulation
News Publication Date: 9-Jan-2026
Web References: 10.1021/acsami.5c17943
Image Credits: Jorge Vidal/Rice University
Keywords
Mechanical engineering, Surface structure, Mechanical properties
