Chuck Bednar for redOrbit.com – Your Universe Online
Photochromic lenses capable of darkening in response to exposure to ultraviolet radiation and other forms of light have been around for years, but let’s face it: They can be slow to block out the glare quickly, or be equally unreliable when it comes time to return to normal.
Fortunately, researchers from the Georgia Institute of Technology are working on a solution: eyeglass lenses that can quickly go from clear to shaded and back again when you want them to, instead of just passively responding to changes in light. Such technology would be a tremendous benefit to pilots, security guards and other professionals, they explained.
In a recent edition of the journal ACS Applied Materials & Interfaces, Anna Österholm of the Georgia Tech School of Materials Science and Engineering and colleagues from Clayton State University and the BASF Corporation explain how they were able to use predictive color-mixing of electrochromic polymers to create a series of brown ECP blends.
Those blends, they continued, could be used as the active material in electrochromic eyewear that can be controlled by the user, leading to the eventual development of eyewear that could be switched from clear to darkly shaded to back again in response to a small electrical charge.
As Österholm and her colleagues explain, such a device would be a tremendous advance over existing photochromic lenses, which often fail to meet the needs of their users. For instance, if a person is wearing a baseball cap, the lenses often fail to darken, even in bright sunshine. Also, the lenses are often unable to block the brightest rays, such as sun reflected off of snow.
The delay in changing from tinted back to clear can also be a hazard, as the process can take up to several minutes to be completed. This can be time that some people, including airline pilots, simply do not have. Eyeglasses built using the ECP blends could not only overcome those issues, but could also be fine-tuned to match the colors currently available in commercial sunglasses.
“The brown hues created in this study demonstrate how fine-tuning of coloration can be achieved in a straightforward fashion through color mixing of soluble electrochromic polymers without having to devise synthetic routes,” the authors wrote. “This provides access to a wide spectrum of colors without the need to synthesize each individual hue, but rather with only a handful of starting ECP components.”
They noted that each of the blends they came up with were able to switch between colored and clear states in a matter of seconds. Furthermore, they found that blending together the components caused the redox potentials of the components to shift, and the switching speeds for one blend to improve. On the basis of this discovery, they said that the interaction of the polymer compounds is more complex than expected, and was worthy of additional analysis.
“The highest performance blend was incorporated into a solid-state lens prototype with an MCCP counter electrode, where the entire device was assembled using roll-to-roll compatible techniques,” the researchers said. “The lens achieved highly transmissive colored and colorless states with fast switching in a ± 1 V window and a 45% change in transmittance upon a full switch (not subtracting the contributions from the electrolyte and the substrate).”
“The more rapid switching speed of the lens relative to the films results, likely due to the larger surface area and closer placement of the counter electrode, making the lens configuration an ideal device architecture for electrochromic applications,” they added. “The rapid switching kinetics also made the intermediate coloration unnoticeable in the lens.”
Their experiments demonstrated the potential effectiveness of blended ECPs in eyeglasses, both from an aesthetic standpoint and a performance-related one, for use in manually-controlled electrochromic eyewear applications, Österholm and her fellow researchers concluded.
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