PRESS-NEWS.org - Press Release Distribution
PRESS RELEASES DISTRIBUTION

Researchers break a theoretical time barrier on bouncing droplets

MIT research could aid ice prevention, wing efficiency, and more

2013-11-21
(Press-News.org) Contact information: Andrew Carleen
acarleen@mit.edu
617-253-1682
Massachusetts Institute of Technology
Researchers break a theoretical time barrier on bouncing droplets MIT research could aid ice prevention, wing efficiency, and more CAMBRIDGE, Mass-- Those who study hydrophobic materials — water-shedding surfaces such as those found in nature and created in the laboratory — are familiar with a theoretical limit on the time it takes for a water droplet to bounce away from such a surface. But MIT researchers have now found a way to burst through that perceived barrier, reducing the contact time by at least 40 percent.

Their finding is reported in a paper in the journal Nature co-authored by Kripa Varanasi, the Doherty Associate Professor of Mechanical Engineering at MIT, along with James Bird, a former MIT postdoc who is now an assistant professor of mechanical engineering at Boston University, former MIT postdoc Rajeev Dhiman, and recent MIT PhD recipient Hyukmin Kwon.

"The time that the drop stays in contact with a surface is important because it controls the exchange of mass, momentum, and energy between the drop and the surface," Varanasi says. "If you can get the drops to bounce faster, that can have many advantages."

For example, in trying to prevent the buildup of ice on an airplane wing, the contact time of raindrops is critical: The longer a droplet stays in contact with a surface before bouncing off, the greater its chances of freezing in place.

According to the theoretical limit, the minimum time a bouncing droplet can stay in contact with a surface — first spreading out into a pancake-like shape, then pulling back inward due to surface tension and bouncing away — depends on the time period of oscillations in a vibrating drop, also known as the Rayleigh time. The way to achieve that minimum contact time, the conventional wisdom holds, is to minimize interaction between the water and the surface, such as by creating low-adhesion superhydrophobic surfaces.

But Varanasi's team found that increasing the surface interaction in a particular way can speed the process beyond that previous limit. To facilitate this interaction, they added macroscopic features — such as ridges that break a droplet's symmetry and can serve to split it, causing it to recoil in highly irregular shapes. These ridged surfaces can have contact times that are 40 percent shorter than control surfaces.

"We've demonstrated that we can use surface texture to reshape a drop as it recoils, in such a way that the overall contact time is significantly reduced," says Bird, the paper's lead author. "The upshot is that the surface stays drier longer if this contact time is reduced, which has the potential to be useful for a variety of applications."

With this reduction in contact time, the researchers were able to show that droplets bounced off before freezing on these symmetry-breaking surfaces; on control surfaces, droplets arrested and solidified on the surface. "We can reduce it further," Varanasi says, through optimization of the texture. "I hope we can manage to get a 70 to 80 percent reduction."

Varanasi's team's findings may also have implications for ecology: The researchers found that some butterfly wings naturally produce the same effect, limiting the likelihood that water will spread out over the wings and curtail their aerodynamic properties — a clear survival advantage. (In the case of the wings, it is the veins within that create the droplet-busting surface ridges.)

Similarly, the veins of nasturtium leaves, unlike those of most leaves, are on top, where they serve to break up droplets that land there. The MIT researchers found that drops bounced off both butterfly wings and nasturtium leaves faster than they bounced off lotus leaves, which are often considered the "gold standard" of nonwetting surfaces.

Varanasi points out that creating the needed surface textures is actually very simple: The ridges can be produced by ordinary milling tools, such as on the surface of an aluminum plate, making the process scalable to industrial levels. Such textures could also be created on fabric surfaces, he says, as a potential replacement for existing waterproof coatings whose safety has been called into question by the Environmental Protection Agency.

In addition to waterproofing and prevention of surface icing, the technique could have applications in other areas, Varanasi says. For example, the turbine blades in electric power plants become less efficient if water builds up on their surfaces. "If you can make the blades stay dry longer, you get a bump up in efficiency," he says. The new technique could also reduce corrosion on surfaces where droplets, especially if they are acidic or contain contaminants, contribute to degradation.

### Written by David Chandler, MIT News Office


ELSE PRESS RELEASES FROM THIS DATE:

Research uncovers secrets of Mars' birth from unique meteorite

2013-11-21
Research uncovers secrets of Mars' birth from unique meteorite TALLAHASSEE, Fla. - As NASA prepares to launch a new Martian probe, a Florida State University scientist has uncovered what may be the first recognized example of ancient Martian crust. The ...

Tiny antisense molecules increase 'good cholesterol' levels in obese primates

2013-11-21
Tiny antisense molecules increase 'good cholesterol' levels in obese primates Targeting shared nucleotide sequences can suppress family of gene-regulating microRNAs A strategy developed by Massachusetts General Hospital (MGH)-based investigators to increase ...

BU, MIT team engineers add new wrinkles to waterproofing

2013-11-21
BU, MIT team engineers add new wrinkles to waterproofing A surface that repels fluids faster VIDEO: The clock at top shows how fast a drop bounces off a relatively ...

Ancient Siberian genome reveals genetic origins of Native Americans

2013-11-21
Ancient Siberian genome reveals genetic origins of Native Americans Genetics The genome sequence of a 24,000-year-old Siberian individual has provided a key piece of the puzzle in the quest for Native American origins. The ancient Siberian demonstrates genomic ...

New health economics study highlights long-term benefits of rotator cuff surgery

2013-11-21
New health economics study highlights long-term benefits of rotator cuff surgery Understanding the full impact of treatments is important for patients with common shoulder injury Rosemont, Ill – Each year, close to 2 million people in the United States ...

Involving patients in their nurses' shift change reduces medical errors and satisfies patients

2013-11-21
Involving patients in their nurses' shift change reduces medical errors and satisfies patients TORONTO, Nov. 20, 2013 – At shift change, incoming and outgoing nurses transfer accountability by exchanging information about the patients under their charge. Called ...

What composes the human heart? U of T researchers crunch the numbers

2013-11-21
What composes the human heart? U of T researchers crunch the numbers A foundational study published in top biomedical journal PNAS (Proceedings of the National Academy of Sciences) this week by researchers at the University of Toronto's Institute of Biomaterials ...

Texas A&M: 24,000-year-old skeletal remains raise new questions about first Americans

2013-11-21
Texas A&M: 24,000-year-old skeletal remains raise new questions about first Americans COLLEGE STATION, Nov. 20, 2013 – Results from a DNA study of a young boy's skeletal remains believed to be 24,000 years old could turn the archaeological world upside down – it's ...

Aging erodes genetic control, but that's flexible

2013-11-21
Aging erodes genetic control, but that's flexible Fly study shows how heterochromatin changes with age, diet PROVIDENCE, R.I. [Brown University] — Biologists at Brown University have found a way to measure the effects of aging by watching the ebb and flow of ...

Let's just harvest invasive species -- problem solved?

2013-11-21
Let's just harvest invasive species -- problem solved? URBANA, Ill. – Although invasive Asian carp have been successfully harvested and served on a dinner plate, harvesting invasive plants to ...

LAST 30 PRESS RELEASES:

Stakeholders meet to discuss national peatland impact plans for Finland, Germany, Netherlands

Physically cold, mentally strained

Consistent policy, not “patchwork” regulations, recommended for the coexistence of crops

LEDs shed light on efficient tomato cultivation

2025 Ig Physics Nobel Prize for perfect pasta sauce

Bright squeezed light in the kilohertz frequency band

Water flowed on ancient asteroid

AI model offers accurate and explainable insights to support autism assessment

Process for dealing with sexual misconduct by doctors requires major reform

Severe pregnancy sickness raises risk of mental health conditions by over 50%

Early humans may have walked from Türkiye to mainland Europe, new groundbreaking research suggests

New study shows biochar’s electrical properties can influence rice field methane emissions

Guangdong faces largest chikungunya outbreak on record

Tirzepatide improves blood sugar control in children aged 10-17 years with type 2 diabetes inadequately controlled on existing therapies (SURPASS-PEDS trial)

An old drug, in a low dose, shown to be safe and effective in preventing progression of type 1 diabetes in children and young people (MELD-ATG trial)

Study reports potential effects of verapamil in slowing progression of type 1 diabetes

Fresh hope for type 1 diabetes as daily pill that slows onset confirms promise at 2-year follow-up

New estimates predict over 4 million missing people who would be alive in 2025 if not for inadequate type 1 diabetes care

So what should we call this – a grue jay?

Chicago Quantum Exchange-led coalition advances to final round in NSF Engine competition

Study identifies candidates for therapeutic targets in pediatric germ cell tumors

Media alert: The global burden of CVD

Study illuminates contributing factors to blood vessel leakage

What nations around the world can learn from Ukraine

Mixing tree species does not always make forests more drought-resilient

Public confidence in U.S. health agencies slides, fueled by declines among Democrats

“Quantum squeezing” a nanoscale particle for the first time

El Niño spurs extreme daily rain events despite drier monsoons in India

Two studies explore the genomic diversity of deadly mosquito vectors

Zebra finches categorize their vocal calls by meaning

[Press-News.org] Researchers break a theoretical time barrier on bouncing droplets
MIT research could aid ice prevention, wing efficiency, and more