#omniphobic

Researchers have developed a new mechanism to make water droplets slip off surfaces, described in a paper published in Nature Chemistry. The discovery challenges existing ideas about friction between solid surfaces and water and opens up a new avenue for studying droplet slipperiness at the molecular level. The new technique has applications in a range of fields, including plumbing, optics, and the auto and maritime industries. All around us, water is always interacting with solid surfaces. Cooking, transportation, optics and hundreds of other technologies are affected by how water sticks to surfaces or slides off them. Understanding the molecular dynamics of these microscopic droplets helps scientists and engineers find ways to improve many household and industrial technologies. Liquid-like surfaces are a new type of droplet-repellent surface that offer many technical benefits over traditional approaches -- a topic recently reviewed in Nature Reviews Chemistry by Aalto University professor Robin Ras. They have molecular layers that are highly mobile yet covalently tethered to the substrate, giving solid surfaces a liquid-like quality that acts like a layer of lubricant between the water droplets and the surface itself. A research team led by Ras used a specially-designed reactor to create a liquid-like layer of molecules, called self-assembled monolayers (SAMs), on top of a silicon surface.

New coating can eliminate complex disinfectant procedures for protective face shields

Acting like an invisible force field, a new liquid coating being developed by UBC Okanagan researchers may provide an extra layer of protection for front-line workers.

Researchers at the Okanagan Polymer Engineering Research and Applications (OPERA) Lab have developed a coating that repels nearly all substances off a surface. And that new coating will make cleaning personal protective equipment a little bit easier for front-line health care workers, explains Kevin Golovin, an assistant professor at UBCO's School of Engineering and director at OPERA.

Surfaces that can repel a broad range of liquids are called omniphobic, explains UBCO master's student and lead author of the study Behrooz Khatir. Working in Golovin's lab, Khatir has created a spray-on solution that can make any surface, including a face shield, omniphobic.

"Omniphobic -- all-liquid repellent -- films can repel a broad range of liquids, but the applicability of these coatings has always been limited to silicon wafers or smooth glass," says Khatir. "This new formulation can coat and protect just about any surface, including metals, paper, ceramics and even plastics."

The two-layer coating involves placing an ultra-smooth silica layer on a surface and then functionalizing this layer with a highly-reactive silicone to effectively block all kinds of liquids from sticking on the surface, explains Golovin.

Surface science concepts are up for revision

The textbook directions for characterizing the wetting properties of solid surfaces are likely to change as KAUST researchers demonstrate that conventional tests can be misleading.

Current go-to methods to determine surface wetting characteristics rely on measuring contact angles, whereby images of advancing and retracting droplets dispensed by capillaries onto surfaces are analyzed to estimate angles at solid-liquid-vapor interfaces.

A contact angle exceeding 90 degrees for water- or oil-based droplets indicates surfaces are hydrophobic (water repelling) or oleophobic (resistant to oil). Therefore, surfaces that meet this criterion for both water and oils are defined as omniphobic. High contact angles also ensure that, when immersed in liquids, surfaces entrap air, which is crucial for applications, such as desalination, drag reduction in transport pipes and antifouling materials for ships.

Contact angles have proven extremely reliable for assessing the omniphobicity of surfaces that exploit liquid-repellent chemical coatings. Commercially available equipment and software exist for measuring real-time contact angles. However, in exploring coating-free approaches to repel liquids, Himanshu Mishra's team found that assessments based only on contact angles can be deceptive.

Novel Surface Design Overcomes Condensation, Offers New Approach to Liquid-Repelling Surfaces

“Omniphobic” might sound like a way to describe someone who is afraid of everything, but it actually refers to a special type of surface that repels virtually any liquid. Such surfaces could potentially be used in everything from ship hulls that reduce drag and increase efficiency, to coverings that resist stains and protect against damaging chemicals. But the omniphobic surfaces developed so far suffer from a major problem: Condensation can quickly disable their liquid-shedding properties.

Now, researchers at MIT have found a way to overcome this effect, producing a surface design that drastically reduces the effects of condensation, although at a slight sacrifice in performance. The new findings are described in the journal ACS Nano, in a paper by graduate student Kyle Wilke, professor of mechanical engineering and department head Evelyn Wang, and two others.

Creating a surface that can shed virtually all liquids requires a precise kind of texture that creates an array of microscopic air pockets separated by pillars or ridges. These air pockets keep most of the liquid away from direct contact with the surface, preventing it from “wetting,” or spreading out to cover a whole surface. Instead, the liquid beads up into droplets.

Repellent research: Navy developing ship coatings to reduce fuel, energy costs

It can repel water, oil, alcohol and even peanut butter. And it might save the U.S. Navy millions of dollars in ship fuel costs, reduce the amount of energy that vessels consume and improve operational efficiency.

The Office of Naval Research (ONR) is sponsoring work by Dr. Anish Tuteja, an associate professor of materials science and engineering at the University of Michigan, to develop a new type of "omniphobic" coating. This chemical coating is clear, durable, can be applied to numerous surfaces and sheds just about any liquid.

Of particular interest to the Navy is how omniphobic coatings can reduce friction drag -- resistance created by the movement of a hull through water -- on ships, submarines and unmanned underwater vessels.

Compare friction drag to jogging through a swimming pool. Because of the water's resistance, each stride is more difficult and requires more energy and effort.

'Everything-repellent' coating could kidproof phones, homes

In an advance that could grime-proof phone screens, countertops, camera lenses and countless other everyday items, a materials science researcher at the University of Michigan has demonstrated a smooth, durable, clear coating that swiftly sheds water, oils, alcohols and, yes, peanut butter.

Called "omniphobic" in materials science parlance, the new coating repels just about every known liquid. It's the latest in a series of breakthrough coatings from the lab of Anish Tuteja, U-M associate professor of materials science and engineering. The team's earlier efforts produced durable coatings that repelled ice and water, and a more fragile omniphobic coating. The new omniphobic coating is the first that's durable and clear. Easily applied to virtually any surface, it's detailed in a paper published in ACS Applied Materials & Interfaces.

Tuteja envisions the new coating as a way to prevent surfaces from getting grimy, both in home and industry. It could work on computer displays, tables, floors and walls, for example.

"I have a 2-year-old at home, so for me, this particular project was about more than just the science," Tuteja said. "We're excited about what this could do to make homes and daycares cleaner places, and we're looking at a variety of possible applications in industry as well."

Bio-inspired materials decrease drag for liquids

An eco-friendly, coating-free strategy has been developed to make solid surfaces liquid-repellent, which is crucial for the transportation of large quantities of liquids through pipes. Researchers from KAUST's Water Desalination and Reuse Center have engineered nature-inspired surfaces that decrease frictional drag at the interface between liquid and pipe surface.

Piping networks are ubiquitous to many industrial processes ranging from the transport of crude and refined petroleum to irrigation and water desalination. However, frictional drag at the liquid-solid interface reduces the efficiency of these processes.

Conventional methods to reduce drag rely solely on chemical coatings, which generally consist of perfluorinated compounds. When applied to rough surfaces, these coatings tend to trap air at the liquid-solid interface, which reduces contact between the liquid and the solid surface. Consequently this enhances the surface omniphobicity, or ability to repel both water- and oil-based liquids.

"But if the coatings get damaged, then you are in trouble," says team leader Himanshu Mishra, noting that coatings breakdown under abrasive and elevated temperature conditions.

Navy is developing coatings for ships that may reduce fuel, energy costs 40-80%

❝ It can repel water, oil, alcohol and even peanut butter. And it might save the U.S. Navy millions of dollars in ship fuel costs, reduce the amount of energy that vessels consume and improve operational efficiency.

The Office of Naval Research (ONR) is sponsoring work by Dr. Anish Tuteja, an associate professor of materials science and engineering at the University of Michigan, to develop a new…