Secondary Secondary Science

Secondary Science – 50 years of LCDs

What is the connection between watching TV and heart attacks?  No, it’s not that too much of the former can cause the latter although that could be true.  The answer is liquid crystals.  Liquid crystal displays (LCDs) are now everywhere you look – TV screens, computer display screens, clocks, calculators – just about anything that has a digital display.

In 1888 in Prague, Friedrich Reinitzer discovered some unusual properties of compounds derived from cholesterol.  Cholesterol is an important chemical involved in the metabolism of fats – that’s the connection to heart attacks.  Reinitzer found that when these compounds were heated and cooled they didn’t behave like normal solids and liquids.  Solids normally turn into a clear liquid at the melting point.  Reinitzer’s compounds became a viscous white fluid at one temperature and only turned into a typical clear liquid at a higher temperature.  They have a state between solid and liquid which was given the name liquid crystal.  Some of the compounds show colour changes during the liquid crystal phase and are used in thermometers.

The compounds that have a liquid crystal state are long, thin rod-like molecules.  They usually have at least one ring of six carbon atoms that keep the molecules rigid.  In the solid state the molecules are packed tightly together.  In the liquid state they are jumbled and can move.  In the liquid crystal state the molecules can move around but remain lined up in the same direction.  The discovery of the liquid crystals caused some interest amongst chemists but they were not thought to have any use – until 1962.

RCA (The Radio Corporation of America) was the world’s leading developer and manufacturer of televisions – what we now think of as the old, heavy, bulky boxes containing a CRT (cathode ray tube).  RCA had developed electronic black and white television in the 1930s and colour TV in the 1950s. In the late 1950s and 60s the company was interested in all types of display technology but the scientists at company laboratories in Princeton, USA,  were largely allowed to follow any line of research they liked. Richard Williams, a physical chemist joined the laboratories in 1958. Williams was interested in the properties of semiconductors and liquid crystals.

It was already known that liquid crystals had unusual electrical properties.  They were anisotropic.  This means that the properties change with direction.  Like graphite, liquid crystals conduct electricity better in one plane than in the other planes at right angles.  In 1962 Williams devised an experiment.  He sandwiched a liquid crystal material between two glass plates that had been given a transparent conductive coating.  He connected the plates to a source of electricity.  Then he heated the plate gently so that the material changed state from solid to liquid crystal.  When he turned on the electricity he noticed a regular pattern of light and dark appear in the material which disappeared when he turned the electricity off.  The patterns are now called Williams domains.

Williams shared his work with a young chemist, George Heilmeier.  Williams went off on other lines of research but Heilmeier was fascinated by Williams’ discovery.  He realised immediately that the discovery could be used as a basis for a type of display that could be packed into flat screens.  He set to work and soon made more discoveries leading to the development of a simple panel that changed from light to dark when an electric current was passed through it.  One problem was to find materials that were liquid crystals at room temperature.  Heilmeier’s team made progress and in 1968 RCA showed to the world the first working liquid crystal display.

Strangely the bosses of RCA weren’t impressed.  LCDs were a very different technology to the cathode ray tubes that the company sold around the world and which they thought would be the source of the company’s fortunes forever.  RCA abandoned research in LCDs and Heilmeier and his team left the company.

The Japanese company, Sharp, however had seen RCA’s show and were interested.  In a fever of research and development they had the first LCD calculator on the market in 1973.  Soon after LCD watches appeared.   During this time new liquid crystal materials were discovered and manufactured in the UK, Germany and Switzerland that had a wider and more useful temperature ranges and were more stable.  The techniques for switching the liquid crystals between light and dark developed so that the size and speed of the displays could be increased.  At last, in 1988 Sharp announced the first 14inch display unit suitable for use as a television.  It was 1/13th the width and 1/4th the weight of traditional TVs with the same size screen.  Since then the size and performance of flat screen LCD TVs and computer displays has increased and they have become very common.  In 2007 more LCD televisions were sold than traditional types and since then the manufacture of CRT televisions has practically ceased; even RCA now sells LCD televisions.  The LCD has taken over – for how long?

Activities

1            Look around your house or school and make a list of all the items that have an LCD.

2           Why do you think LCD televisions have replaced the older CRT TVs?

3           In what ways are liquid crystals like (a) solids, (b) liquids?

4           Reinitzer’s cholesterol derivatives were liquid crystals between about 120oC and 180oC.  Why was it important to find compounds that were liquid crystals between about -10oC and 50oC?

5          The first LCD digital watches were expensive and their displays lasted for about five years.  Why do you think they were popular?

6          What contribution did chemists make to the development of flat screen TVs and computer monitors?

7          It took less than twenty years for LCD technology to replace cathode ray tubes in TVs.  What other examples are there of a new technology replacing an older one?  What do you think will be next for replacement?

8         Why do you think RCA gave up on LCD research while Sharp (and other companies) took it on?

 

Peter Ellis

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