February 11, 2011 6:58:00 AM
I think the first time I heard of liquid crystals, they were used for a silly purpose, within the Mood Rings which were a fad 30 years ago. The "gem" held by the ring changed color; the color-change was based on the temperature of the finger, and of course that had nothing to do with the wearer''s mood.
Liquid crystals have become considerably more important since then, and Mood Rings are not even mentioned by name in "Soap, Science, & Flat-Screen TVs: A History of Liquid Crystals" by David Dunmur and Tim Sluckin. The authors, both of whom have done research on the liquid crystals which we take for granted in modern television and laptop displays, have included a good deal of science within this history.
Much of it is in technical boxes with titles like "Selective reflection from cholesteric liquid crystals," and those of us not in the field are perhaps going to have to let eyes glaze over the detailed science. As a history, though, this is a readable introduction to an influential field, concentrating on personalities within political eras, and demonstrating that as complicated as the science might get, it is still a human endeavor, with all the attendant ambition, misunderstanding, dead ends and eventual enlightenment.
The authors start with a surprising bit of scientific history; though we no longer include Aristotle''s category of fire among the elements, air, water and earth do well to stand for gases, liquids and solids, categories with which all of us are familiar. There is a fourth state called a plasma, about which the authors say, "Do not be deceived. This is simply the gaseous equivalent of a metal, and it is not very common." There aren''t free-standing plasmas on our Earth, for instance (although they are in, say, florescent lights). The fourth state of matter (and we can forgive the authors'' enthusiasm for their own area of research) is really liquid crystals, and they aren''t just in Mood Rings and liquid crystal displays (LCD). They are present in nature; the membranes around our cells are liquid crystals, for instance, and liquid crystals probably played an essential role when life was being evolved. "Liquid crystals were missed by the Greeks," say the authors, "because they do not readily proclaim their existence. They can be identified only by those with skill and experience ..."
And so it was that the German biologist Friedrich Reinitzer in 1888, in his obsession with carrot chemistry, was observing the changing colors as cholesterol compounds derived from carrots changed temperature. The compounds didn''t simply change from solid to liquid, but seemed to have two melting points, going cloudy and clear with dramatic colors in between. Reinitzer was not a chemist, and somehow found Dr. Otto Lehmann who had a controlled-temperature microscope and polarized light viewing. Lehmann was convinced that the materials flowed and were also crystalline. He produced beautiful colored drawings of liquid crystal droplets, but not everyone could accept the seeming contradiction of crystals and liquidity.
Opponents drew upon sarcasm and said that Lehmann''s samples were perhaps just contaminated or badly measured. They also argued, wrongly as it turns out, that liquid crystals were just laboratory artifacts, and were not natural phenomena. There are fine examples of Teutonic vituperation here; the authors say that the arguments "were venomous and vicious personal conflicts manifesting themselves as wars of words, which continued to the grave, and even beyond, while the science itself moved on."
Further work in labs verified the validity of the liquid crystal concept. While the shape of the molecules and the resultant phases they go through were complicated, by the 1920s it was realized that liquid crystals showed the relationship between molecular shape and crystal forms. The essential step of making mathematical models of the behavior of liquid crystals was begun in the early 20th century, and making better models has been one of the most important ways of understanding what the crystals do and how to use them. Indeed, in 1911 the "twisted nematic" structure of certain crystals was described, but they were not modeled mathematically until 1970. The theory produced proved to be a breakthrough, and it was this particular structure that made possible the liquid crystal displays we use every day.
That liquid crystals could be put to use would have surprised the researchers trying to figure them out in the first half of the 20th century. Even in the booming German chemical industry, where for example liquid crystals were for sale in the Merck catalogue, there was no inkling that the chemicals might be exploited for electrical or optical tools, and only the new theories and solid-state physics would open that window. There were many scientific advances under fire during World War II, but liquid crystals were not among them. "Research on liquid crystals had no perceived military value," say the authors, "and so had not been a priority during the war years, although now in the twenty-first century no military force could function without liquid crystal displays." The war would have its effects on researchers, though. The Russian physicist V. K. Frederiks had been arrested in one of the purges in the Soviet Union in 1936. He was to remain in the Gulag until the war, and to die there around 1943. His understanding of how liquid crystals might work in displays (the "Frederiks Effect" describes how a critical minimum voltage or magnetic field is needed to cause a change in display) leads the authors to say that he was the inventor of the modern liquid crystal display.
It was in the early 1960s that the "globalization" of liquid crystal research emerged. This was partly because of English becoming the overall language of science, and partly because the USA became involved. In 1956 the far-seeing Chairman of the Board of RCA, David Sarnoff, predicted bigger and brighter TV screens that could be hung on the wall. The cathode ray tube TVs had reached a maximum practical size; keeping bigger tubes evacuated would have required massive glass surrounds that would have been too heavy. (A German advertisement in 1971 showing the not-so-distant-future wall-mounted TV was withdrawn after a suit from TV tube manufacturers.) There was a Liquid Crystal Institute formed at Kent State University, and in 1965 there was a conference which RCA researchers attended; one of them remembered that "... while many brilliant scientists were working in the field of liquid crystals, applications to displays in general and television in particular had not yet become apparent." Among the problems that had to be addressed was that any useful liquid crystal had to stay liquid under operating conditions, and not all of the initial ones could do so at low temperatures, so early prototypes included heaters.
The authors are generous in their assessment of the patent rights battles, and list who got the money, including Kent State University and various inventors, but ending with, "The lawyers especially made money." Once Canon, Sharp, Toshiba, and the rest got into the game, it was not long before flat screen TVs entered our homes. There will be better, bigger, cheaper displays from LCDs, but in the final chapter, the authors speculate that liquid crystals may be used against diseases of the cell membranes, or may be the basis for polymers which have untold potential for new uses. Thus, this useful overview of liquid crystal history will need someone to write an update in only a few years.
Rob Hardy is a local psychiatrist who reviews books for a hobby. His e-mail address is [email protected]