Emulsion sandwich controls light transmission

17 Jun 2002

Hitachi Chemical Company is the latest company to obtain a license for production of a film that transmits a variable amount of light. Suspended particle device (SPD) technology, developed by Research Frontiers, allows the amount of light passing through the film to be electrically controlled.

The film has many potential applications including 'smart' windows, eyewear and goggles, 'self-dimmable' car sunroofs and flat panel displays.

SPD film consists of light absorbing polymer particles suspended in an emulsion. The emulsion is sandwiched between two pieces of a transparent material, such as glass, to make a film. Both sides of the sandwich are coated with an electrical conductor. When no voltage is applied the particles are randomly ordered and block some or all of the light. As the voltage increases the particles align and the film becomes more transparent.

Research Frontiers' Patricia Bryant says that SPD film provides an attractive alternative to liquid crystal films. "Liquid crystals allow light transmission to be 'on' or 'off', but they scatter rather than absorb so there is a haze factor even when the device is on. The price of liquid crystal displays is also very high - estimated at between USD 85 and 100 per square foot - we don't have a price for SPD film yet but it is likely to be much cheaper."

Research Frontiers will not develop the potential products itself but is licensing the SPD technology to other companies and will receive a percentage from the resulting sales.

Although no products are currently in production, Bryant says that several of the licensees are in the advanced stages of development. "There is a good possibility of seeing products in the market place next year."

Hitachi Chemical joins Dainippon Ink and Chemicals, GEC, Materials Sciences Corporation, Glaverbel and Hankuk Glass Industries. Vision-ease holds the only exclusive license for SPD technology and is developing eyewear.

SH