The next time you reach for your Transitions庐 glasses, you can thank Dr. Anil Kumar, an associate fellow in the Optical Division at PPG and the latest recipient of ACS's Award for Creative Invention for his contributions in photochromism and variable polarization and leadership in commercialization.
Kumar grew up in New Delhi and earned a BS and MS from Delhi University. He later transferred to the University of Connecticut, earning a PhD in Organic Chemistry. For his thesis, he studied charge transfer mechanism in photo degradation of some of the medications people take and its role in photo-toxicity and photoallergy. This required him to apply his knowledge of organic chemistry, photochemistry and medicinal chemistry. According to Kumar, 鈥淚t was something I was very interested in, and something PPG was moving toward with its photochromic research.鈥�
He joined Pittsburgh-based PPG in 1991 to study photodegradation (fatigue) of dyes in photochromic lenses, and help develop 鈥済ood, stable and high performing鈥� dyes for plastic lenses (this capability was already available in glass lenses).
Finding Success
Photochromism is a photo-induced color change that also reverts back to clear state via thermal or photo process, depending on the type. Photochromic lenses are made primarily of plastic, glass or polycarbonate and are embedded with millions of molecules, including silver chloride or silver halide. The molecules in lenses are transparent and colorless until they are exposed to the ultraviolet rays of sunlight, at which point, they isomerize and change shape to a longer conjugated chromophore, causing the lenses to darken.
In partnership with Transitions Optical (then a joint venture of PPG and French eyewear company, Essilor), the team produced Transitions Plus庐, the first commercially successful photochromic plastic lens. The original lens has been followed by several generations of improved products.
Also called adaptive lenses, Transitions庐 lenses (the most popular brand of photochromic lenses) are transparent indoors and at night and automatically darken outdoors, blocking UV rays and bad blue light, while they help to enhance contrast and reduce glare.
Continued Innovation
Kumar wanted to develop a version of the lens that would not only darken as conditions change but also polarize in the darkened state. That required a dye that would be clear indoors and dark outdoors, but when dark it orients itself in a fashion that generates polarization in a specific direction. It would also require developing new and scalable production procedures, he says.
The team has continued to innovate with the dyes, materials and processes, launching Transitions Vantage庐, the first clear-to-polarized product. In addition to providing protection from bright sunlight, the key advantage with clear-to-polarized lenses is the reduction of blinding glare and light scatter reflecting off surfaces.
In 2014, Essilor acquired the entire stake in Transitions庐, however PPG still maintains the R&D function. Kumar鈥檚 team continues to innovate to further improve the performance and develop novel dyes and materials that were eventually used in the Transitions庐 XTRActive Polarized product, introduced in January 2021. The XTRActive Polarized lenses start out as clear indoors and polarize outdoors in the sun with fast-reacting dichroic dyes which achieve up to 90% polarization efficiency.
Each lens starts as a plastic lens substrate, which basically looks like a small, clear hockey puck, and then various layers and coatings are added one after another, some thermal-cured, and some photo-cured. When the 鈥渉ockey puck鈥� is fully layered, the plastic piece is then ground back using a special milling machine to adjust for a person鈥檚 specific prescription and to fit into a frame. The end product weighs about 5%-10% of its original weight, depending on the prescription. Naturally, there are many considerations to getting it just right. 鈥淎ll these layers have to survive that process and maintain their ophthalmic quality with no distortions,鈥� says Kumar. 鈥淚t also has to be stable for the duration of prescription.鈥�
Unique in the industry, the lenses are also designed to reduce bright light while driving. 鈥淭he dyes we developed had to work with the smaller amount of high energy visible light coming through the windshield,鈥� Kumar says. 鈥淲e call this XTRAactive dyes.鈥�
What鈥檚 Next?
Kumar and his team at PPG continue to develop new materials, dyes and processes to help the huge number of people around the world who need vision correction and want products that also protect their eyes from UV, blue light and outdoor glare. 鈥淭here are some exciting projects we鈥檙e working on now that will hit the market in future,鈥� he hints.
As an Associate Fellow and Senior Researcher, Kumar oversees a scientific team and also gets involved in new partnerships hoping to use the team鈥檚 knowledge and expertise in novel applications in the areas, such as security, sensors, displays, switches, windows, etc.
鈥淭here are many possible markets for our materials and technologies,鈥� he notes. 鈥淎s a scientist, I love coming up with new ideas and providing answers to challenging problems that make my creative juices flow.鈥�
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