Gizmorama - July 4, 2018
Are way of waterproofing is going to change. Soon polymers will be banned, due to environmental concerns. MIT is currently working hard to develop a new and improved waterproofing material that not only benefits us, but the environment, too.
Learn about this and more interesting stories from the scientific community in today's issue.
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* The 'retroreflector' reflects sound in the direction it came from *
Scientists have developed a superior sound-reflecting material. The "retroreflector" technology can bounce back sound waves in the direction they came from.
Previous retroreflectors relied on a combination of angled reflections to return sound waves to their source direction, but the latest material offers a direct reflection. The new technology allows the material to perform at a wider effective range, reflecting sound waves across a range of 70 degrees in either direction.
"The technology makes use of two engineered materials," Yun Jing, an associate professor of mechanical and aerospace engineering at North Carolina State University, said in a news release. "The first layer focuses the incoming sound waves onto a second layer, which then sends the sound waves back to their source. We were inspired by a similar approach used in optics research, but we think we are the first to use this technique in the acoustics field."
Previous retroreflector technologies used an array of rectangular pits, which directed sound waves to the bottom of the pits before redirecting them back to where they came from.
"Designs using that approach can be bulky, and have a fairly narrow range of angles that they can reflect properly," Jing said. "Our technology is both slimmer and effective across a wider range of angles."
The new retroreflector composite material is both effective and efficient. When sound waves hit the technology at perpendicular angle, 60 percent of the sonic waves are returned. When sound waves strike at a 70 degree angle, 40 percent of the waves are reflected.
Scientists described their technology this week in the journal Physical Review Letters.
"We have a fully functional prototype now, and our next steps include fine-tuning the technology for use in specific applications, such as medical ultrasound," Jing said. "Frankly, we think there are likely applications that we haven't thought of yet."
Acoustic retroreflectors could prove useful for a variety of technologies -- including music and communications-related technologies -- that rely on sound waves to function properly.
*-- New, safer waterproof coating invented by MIT scientists --*
Traditional waterproofing compounds, long-chain polymers, accumulate and persist in the environment and the human body, posing health concerns. Environmental regulators are expected to soon ban the use of the polymers.
As a result, material scientists are looking for a safer way to waterproof materials.
Researchers at MIT have developed a new type of coating. Not only is the new coating safer, it also works better, its inventors claim.
"Most fabrics that say 'water-repellent' are actually water-resistant. If you're standing out in the rain, eventually water will get through," MIT professor Kripa Varanasi said in a news release. "The goal is to be repellent -- to have the drops just bounce back."
All sorts of products rely on waterproofing, but traditional hydrophobic technologies suffer several problems. Most waterproofing coatings are liquid-based. Fabrics must be entirely submerged and then dried. The technique limits breathability.
To reopen sealed-over pores in the fabric, air is blown through the material, an additional manufacturing step. The additional step increases production costs and undermines the waterproofing effect.
The solution developed by Karanasi and his colleagues combines short-chain polymers, which don't accumulate as easily or persist in the environment, with a coating process called initiated chemical vapor deposition, or iCVD.
Researchers described the technology this week in the journal Advanced Functional Materials.
The technique doesn't involve liquids. Instead, the application process allows the polymer to form to the contours of the fabric's fibers without clogging pores. An added sand-blasting step can enhance the coating hydrophobic effect, but is not necessary.
"The biggest challenge was finding the sweet spot where performance, durability, and iCVD compatibility could work together and deliver the best performance," said former MIT postdoc Dan Soto.
Lab tests proved the coating technology works to waterproof a variety of fabrics and materials against a variety of liquids, including coffee, soy sauce, ketchup and sodium hydroxide. The coatings integrity also survived repeated washing and abrasion tests.
"Many fabrics can benefit from this technology," Varanasi said. "There's a lot of potential here."
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