American Scientist

To the Editors:

I thoroughly enjoyed Roger Mortimer’s article “Switching Colors with Electricity” in the January–February issue of American Scientist . I was pleasantly surprised to learn that so much progress has been made toward advancing electrochromic technology over the past few years. This excellent review of the early history of electrochromics brought back memories of the work I did back in the 1960s when I was a research scientist at RCA Laboratories in Princeton, New Jersey.

At that time, my late colleague Joel Goldmacher and I were primarily interested in liquid crystals for possible use in a flat-screen television display. We focused our attention on liquid crystals, synthesizing materials that eventually led us to formulate the first room-temperature nematic liquid crystals, which led to the fabrication of the first practical liquid crystal display built by our colleague George Heilmeier in 1966.

I also did quite a bit of work extending Heilmeier’s guest-host effect , the electric field orientation of dichroic dyes in liquid crystals, a process we called “electronic color switching.” We even succeeded in building a multi-color display using three liquid crystal layers, each with a subtractive color dichroic dye; one with magenta, one with yellow and one with cyan. With the exception of some digital clock products, that technology was never widely used commercially and was replaced by the color filter technology generally used today.

In the 1970s, we also investigated electrochromics, particularly viologen and tungsten oxide, as possible alternatives. However, we found that fatigue was a problem with those materials since the performance would degrade after many cycles of ON and OFF operation.

Ultimately, I spent another decade of my career in the development and manufacturing of LCDs. Then in 1978, I started a consulting company and in the mid-1980s I again encountered electrochromics when several of my clients were investigating the technology. However, they were never able to solve the fatigue problem and dropped the research. As mentioned in Mortimer’s article, it was Gentex that solved the problem and made the most significant advances, becoming the leader in development and manufacture of electrochromic mirrors.

Another related electronic color switching technology is the electrophoretic display, first reported by I. Ota of Matsushita Electric in 1973. This technology was investigated by many companies in the 1970s and 1980s. Several of my clients, including Philips and Exxon, also investigated these displays, but they could not solve the same fatigue problem that plagued early electrochromic displays. However, in recent years a company called E-Ink successfully developed and built commercially available electrophoretic displays now used in the popular Kindle reader. E-Ink has partnered with many companies and the technology continues to improve.

I wish Mortimer great success in his research on these interesting electrochromic materials, which show great promise for future applications.

Joseph A. Castellano
San José State University, Emeritus
San José, CA