Michael Nosonovsky is Associate Professor of Engineering at the University of Wisconsin-Milwaukee. His research focuses on tribology (the study of friction) and the surface sciences, bio-mimetic materials and water-related physicochemical surface phenomena such as wetting, capillary force, and adhesion, as well as the mechanical properties of omniphobic substances, including self-healing, self-lubricating, self-cleaning compounds. His recent publications include Tribology for Scientists and Engineers (2013) and the forthcoming Friction-Induced Vibrations and Self-Organization: Mechanics and Non-Equilibrium Thermodynamics of Sliding Contact.
(This interview is reprinted from Intersections, a monthly newsletter of the Center for International Education, December 11, 2015)
Michael, thanks for taking a moment to talk with me. I’m somewhat familiar with the terminology of your specialization from my days of studying biology for my B.A. and from working in prosthetics and orthopedics, both parts of the medical field that are very concerned with mechanical engineering on a human scale. Unless I’m wrong, your work involves substances and compounds that don’t stick to anything, correct? Tell us more about your work and what implications it has for water, people, and policy.
My research is in the surface science. This is an important area of the materials science, because properties of any material at its surface are often different from those in the bulk. A famous physicist, Wolfgang Pauli, once said: “if God made bulk material, surfaces were invented by the devil.” Surface properties are particularly important when you deal with very small objects or devices, say, in nanotechnology. When you are trying to build a very small device, surface forces, such as friction or adhesion, become very strong and dominate over other forces.
Here at UWM we study how to control surface profile in order to obtain desirable properties. Part of this is superhydrophobicity, or the ability of certain cleverly-engineered surfaces to repel water. Superhydrophobic surfaces also tend to repel dirt, and this property is called “self-cleaning.” Interestingly, scientists learned about superhydrophobicity from plants. For centuries, the lotus was a symbol of purity in India and China because its leaves emerge clean and dry from muddy water. The lotus is shown in many Buddhist paintings, where it served as a symbol of both material and spiritual purity. An ancient Hindu poem, Bhagavat Gita, says about the seeker of truth: “Having abandoned attachment, one acts unattained by evil, just as a lotus leaf is not wetted.”
Only 20 years ago, when new types of microscopes were invented, scientists learned why the lotus repels water and dirt: the lotus leaf’s surface has a complex hierarchical structure. There are microscopic bumps upon which there is a layer of wax with much smaller, nanoscale bumps. None of these three factors, microbumps, nanobumps, and wax, can result in superhydrophobicity when taken separately, but combined together they lead to the “lotus effect,” meaning superhydrophobicity and self-cleaning. Engineers then began to mimic this for artificial surfaces made of metals, polymers, ceramics, and all kinds of other materials. Mimicking living nature for engineering applications is called “biomimetics.”
On the basis of the lotus effect and superhydrophobicity, new similar effects were found or suggested, incuding non-adhesive “omniphobic” surfaces which repel everything, both water and organic liquids, new types of filtering membranes, underwater self-clearning and oleophobicity to reduce fouling of materials which operate underwater, new biomedical devices to reduce blood stagnation, icephobic substances, and many others. Many of these have direct application to water industry, including self-cleaning pipes and water components such as water heaters and meters, which we are developing here at UWM in collaboration with local companies. Another important direction is water-repellant materials for civil infrastructure, such as concrete and asphalt.
Can you give us any early hints at what we might hear about in your presentation in April, or is it too early still?
Besides the superhydrophobic concrete which I have mentioned, we want to understand how superhydrophobicity can be used for corrosion resistance and to repel ice. From the point of view of a chemist or physicist, water has very unusual properties: it expands when it freezes (water is denser than ice). Water also leads to an unusual type of molecular interactions called “hydrophobic interactions.” Ice is even more interesting and complex than water; just think about how complex the shape and symmetry of a snowflake is (an ice crystal) in comparison with a spherical water droplet. If we understand the fundamental mechanisms of how hierarchical surface roughness can control water adhesion to solids, the next step is to deal with ice adhesion. Icephobicity has many potential applications, especially in a place like Milwaukee where the climate is cold in the winter and a water-centric city becomes a snow-centric city!
Is there a specific text about water and mechanical engineering that you’d recommend to someone who was just becoming interested in the subject? I realize with the specificity of your work that there’s probably no “perfect” text for this, but is there perhaps one primary text that’s invaluable or fundamential to your work?
There was a nice popular paper in New Scientist in 2012 by Jessica Griggs called “Omniphobia: the stuffs that stick at nothing.” We also have several books which were written and published on the topic here at UWM, including Biomimetics in Materials Science: Self-Healing, Self-Lubricating, and Self-Cleaning Materials and Green Tribology: Biomimetics, Energy Conservation, and Sustainability. You can also read my News and Views paper in Nature called “Slippery When Wetted.”
I’m completely intrigued to see what your research will bring to our interdisciplinary CIE conference in April, and what sorts of conversations it will generate. Are there any interdisciplinary topics concerning water-centric cities that you’re looking forward to in particular?
I hope to get better insight into the broader context of the biomimetic approach, in particular, by communicating with my colleagues from the humanities. It is not by chance that engineers and materials scientists started to pay attention to nature. Traditional engineering approaches imply that you have an exact blueprint of your final product and an exact procedure how to make it. Living nature is very different. It has only general algorithms encoded in DNA and hierarchical self-replicating structures, which adjust to the changing environment when they grow. So, instead of concentrating on a rigid homogenous structure and on an exact solution to a problem, the biomimetic paradigm provides a much more flexible and holistic view.
The very difference between natural and artificial (nature and nurture) has become elusive, and the biomimetic approach is an example of that. Interestingly, in social studies and humanities this trend is even more pronounced. My colleagues from social studies state that in a world of circulating cultures and accelerating human movement, all ideals of homogeneity have become irrelevant. This new way of thinking, which biomimetics brings, encourages better harmony between humans and nature. If something mimics nature, it is also ecological. Together with colleagues, we have identified biomimetic surfaces as one of the three areas of ecotribology (or “green tribology”; tribology is the study of friction).
However, on a more practical side, biomimetic materials which repel water, ice, and other substances or resist corrosion also provide cheaper solutions and reduce maintenance costs, such as cleaning, which eventually improves the quality of our lives.
Thanks for taking the time to share your work with us, Michael, and I’m very excited to hear about it at the conference. I’d like to remind our readers to keep an eye on Intersections in the near future for more interviews with our Global Studies Fellows, and information about the CIE conference on Water-Centric Cities, April 15-16, 2016.