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Wikimedia Commons // CC BY-SA 3.0
Wikimedia Commons // CC BY-SA 3.0

How Do Transition Lenses Work?

Wikimedia Commons // CC BY-SA 3.0
Wikimedia Commons // CC BY-SA 3.0

If you’re thinking about getting transition lenses, consider this: Every time you do something as simple as walking out of a building, you could watch a chemical reaction happen literally right in front of your eyes. 

Armed with chemical compounds that spring to action under ultraviolet light, transition lenses darken even on cloudy days to keep out those damaging rays. Then, when the coast is clear, they simply return to transparency. 

Transition or “photochromic” glass was originally developed in the 1960s by Donald Stookey, a chemist at Corning Glass Works and a prolific inventor. (Stookey is most famous for discovering the super durable and extremely popular kitchenware material known as CorningWare, which he actually found accidentally after setting up a test reaction at 900°C instead of 600°C.) Soon after Stookey patented the material, Roger Araujo, another Corning chemist, used his breakthrough to develop the first photochromic lenses.

In 1965, Corning commercialized the first generation of transition lenses under the brand “Bestlite.” Three years later, these were dropped in favor of the more reliable Photogray lenses, named for their bluish gray hue when darkened. This color comes from the tiny amounts of the compound silver chloride (<0.1 percent) dispersed throughout the glass. When exposed to UVA light (315 nm – 400 nm), silver gains an electron from chloride to become silver metal, and gets the ability to absorb visible light and appear darker. They found that this reaction would work with any halogen or element from the same column in the periodic table as chlorine that is capable of giving away one electron to silver. 

The same darkening process is also used for developing photographic film except that film exposure is permanent, while photochromic lenses possess another component, such as copper chloride, that helps silver return to its original, non-absorbing state once it’s away from UV light. 

With the introduction of plastic lenses in the 1980s came the next generation of transition lenses based on thin films of organic compounds. These mostly carbon molecules—such as pyridobenzoxazines, naphthopyrans, and indenonaphthopyrans—react to UVA light by rearranging their chemical bonds into new species that can absorb and essentially block UV and visible light. Like tiny transformers, they can switch between either form depending on the presence or absence of UV light.

Plastic transition lenses are lighter and thinner than their glass counterparts, but their organic films are more susceptible to degradation than the silver halides used in glass.

But for both glass and plastic transition lenses, the darkening process happens almost instantaneously, while becoming clear takes anywhere from three to five minutes—which can be disorienting indoors. The clearing reaction is so much slower because it can’t rely on the driving energy of UV light. One trick to speeding up the reaction is to add heat energy by running the lenses underneath warm water.

Another inconvenience that can’t be avoided as easily comes from modern car windshields. Some are specially designed to filter out UV light, making it difficult for lenses to activate the darkening effect needed for driving.

Transition glasses may or may not be right for you, but they’re an excellent example of the everyday chemistry that’s happening in plain sight.  

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science
New Clear Coating for Everyday Objects Repels Practically All Liquids
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A new clear coating that is said to repel just about everything—peanut butter included—aims to halt the advance of sticky fingers. Developed by researchers at the University of Michigan, the substance can be applied to a variety of surfaces to keep them smudge- and crud-free, including smartphone and laptop screens, windows, walls, and countertops.

Researchers used algorithms to predict which substances would yield an efficient omniphobic coating, or in other words, something capable of repelling oils, alcohols, and other liquids while remaining durable and smooth. Made from a mix of fluorinated polyurethane and a fluid-repellent molecule called F-POSS, the coating can be “sprayed, brushed, dipped, or spin-coated onto a wide variety of surfaces, where it binds tightly,” according to the University of Michigan’s website.

The team’s findings were published in the March issue of the journal ACS Applied Materials Interfaces. Associate professor Anish Tuteja, who headed up the University of Michigan research team, says it could be a godsend for parents of young tots.

"I have a 2-year-old at home, so for me, this particular project was about more than just the science," Tuteja said in a statement. "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."

The team is currently conducting follow-up tests to ensure the coating is nontoxic, but if all checks out, it could find its way into kindergarten classes and daycare centers within the next two years.

Child-proofing everyday objects for the sake of cleanliness isn’t its only potential application, though. The university notes that it could be beneficial to “all industries that depend on the condensation of liquids,” such as refrigeration, power generation, and oil refining.

In recent years, other researchers have set out to create omniphobic coatings, some of which have been successful. However, this undertaking is typically challenging and involves complex synthetic chemistry, according to Chemistry World.

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Food
Why You Never See Fresh Olives at the Grocery Store
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If given a choice, most grocery shoppers prefer fresh produce over something that's been pumped full of preservatives. Yet shoppers are almost never given that choice when it comes to olives. The small, meaty fruits can be found floating in brines, packed in cans, and stuffed with pimentos, but they're hardly ever shipped to the store straight off the tree. As the video series Reactions explains, there's a good reason for that.

In their natural state, because they contain high concentrations of a bitter-tasting compound called oleuropein, fresh olives are practically inedible. To make the food palatable, olive producers have to get rid of these nasty-tasting chemicals, either by soaking them in water, fermenting them in salt brine, or treating them with sodium hydroxide.

Because of its speed, food manufacturers prefer the sodium hydroxide method. Commonly known as lye, sodium hydroxide accelerates the chemical breakdown of oleuropein into compounds that have a less aggressive taste. While other processes can take several weeks to work, sodium hydroxide only takes one week.

Afterward, the olives are washed to remove the caustic lye, then packed with water and salt to extend their shelf life, giving them their distinct briny flavor.

For more on the chemistry of olives, check out the full video from Reactions below.

[h/t Reactions]

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