Engineering the World’s Most Hydrophobic Surfaces: Advancements in Repelling Water Droplets

An artist’s representation of the liquid-like molecular layer repelling water droplets. Credit: Ekaterina Osmekhina/Aalto University

A refined approach to crafting hydrophobic surfaces carries profound implications for a myriad of technologies where the convergence of water and solid materials occurs. This innovation extends its influence across domains as diverse as optics, microfluidics, and culinary arts.

In a groundbreaking development detailed in a recent publication in Nature Chemistry, researchers have unveiled a novel methodology to prompt water droplets to effortlessly slide off surfaces. This breakthrough challenges preconceived notions concerning the interaction between solid surfaces and water, ushering in a new era of scrutiny into droplet mobility at the molecular level. The innovative technique finds applications in a wide spectrum of fields, ranging from plumbing and optics to the automotive and maritime industries.

The Complex Dance of Water and Solid Surfaces

The intricate interplay between water and solid surfaces is a ubiquitous phenomenon. It significantly influences everyday activities such as cooking, transportation, optics, and a plethora of industrial technologies. Gaining an in-depth understanding of the molecular dynamics governing these minuscule droplets empowers scientists and engineers to enhance a multitude of household and industrial applications.

Liquid-like surfaces represent a groundbreaking category of droplet-repellent materials that offer substantial advantages over conventional approaches. As eloquently expounded in a recent review by Professor Robin Ras from Aalto University in Nature Reviews Chemistry, these surfaces are characterized by molecular layers that exhibit high mobility while being covalently bound to the substrate. This unique quality imparts solid surfaces with a fluidic characteristic, akin to a layer of lubrication interposed between water droplets and the surface itself. Professor Ras, along with his research team, employed a specially designed reactor to cultivate a liquid-like layer of molecules, known as self-assembled monolayers (SAMs), atop a silicon surface.

Witnessing the Birth of Self-Assembled Monolayers

Doctoral researcher Sakari Lepikko, the lead author of the study, elucidates, “Our work marks the inaugural attempt to engineer molecularly heterogeneous surfaces at the nanometer scale.” The team adeptly manipulated variables such as temperature and water content within the reactor, allowing them to precisely control the extent to which the silicon surface was enveloped by the monolayer.

Professor Ras adds, “I am enthralled by the integration of the reactor with an ellipsometer, which affords us an extraordinary level of detail in observing the growth of self-assembled monolayers.”

Remarkably, the results indicated heightened droplet slipperiness at both low and high SAM coverage, periods during which the surface exhibits maximum homogeneity. At low coverage, the silicon surface predominates, while at high coverage, SAMs dominate. Contrary to intuition, low coverage encourages water to flow freely between SAM molecules, facilitating its easy removal from the surface. Conversely, at high SAM coverage, water remains on top of the SAM layer and exhibits similar ease of removal. It is only during intermediate coverage levels that water adheres to the SAMs and clings to the surface.

This innovative approach has yielded a liquid surface with unparalleled slipperiness, setting a new standard as the world’s most hydrophobic surface.

Anti-Fogging, De-Icing, Self-Cleaning Applications

The implications of this discovery extend to any scenario demanding droplet-repellent surfaces. According to Lepikko, this encompasses a myriad of situations spanning daily life and industrial solutions. Examples include optimizing heat transfer in pipes, combating ice formation, and mitigating fogging. Moreover, this advancement holds promise in the realm of microfluidics, where precise manipulation of minuscule droplets is imperative, as well as in the development of self-cleaning surfaces. Lepikko concludes, “Our counterintuitive mechanism presents a novel approach to enhancing droplet mobility wherever it is required.”

In the next phase of their research, the team intends to further refine their self-assembling monolayer configuration and enhance the durability of the coating. Lepikko expresses particular enthusiasm for the fundamental scientific insights garnered through this work, which are poised to drive future innovations.

The research, conducted with the support of the national research infrastructure OtaNano, was carried out by the Soft Matter and Wetting group at the Department of Applied Physics. This group has also contributed to the development of other pioneering water-repellent materials.

Reference: “Droplet slipperiness despite surface heterogeneity at molecular scale” by Sakari Lepikko, Ygor Morais Jaques, Muhammad Junaid, Matilda Backholm, Jouko Lahtinen, Jaakko Julin, Ville Jokinen, Timo Sajavaara, Maria Sammalkorpi, Adam S. Foster and Robin H. A. Ras, 23 October 2023, Nature Chemistry. DOI: 10.1038/s41557-023-01346-3

Researchers from the University of Jyväskylä also made substantial contributions to this study.

Frequently Asked Questions (FAQs) about Hydrophobic Surface Engineering

More about Hydrophobic Surface Engineering

• Nature Chemistry
• Aalto University
• University of Jyväskylä
• Self-Assembled Monolayers (SAMs)
• Hydrophobic Surfaces
• Microfluidics
• Heat Transfer in Pipes
• Ice Formation and De-Icing
• Fogging
• Self-Cleaning Surfaces