George Heilmeier George Harry Heilmeier (May 22, 1936 – April 21, 2014) was an American engineer, manager, and a pioneering contributor to liquid crystal displays (LCDs), for which he was inducted into the National Inventors Hall of Fame. Heilmeier's work is a ...

proposed the dynamic scattering effect which causes a strong

scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...

of light when the electric field applied to a special

liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. T ...

mixture exceeds a threshold value. A DSM cell requires the following ingredients:
* a liquid crystal with negative dielectric anisotropy (aligns the LC long axis perpendicular to the electric field), *

homeotropic alignment In liquid crystals Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a ...

of the LC (i.e. perpendicular to the substrate planes), * doping of the LC with a substance that increases the conductivity of the LC to allow a current to flow. With no voltage applied the LC-cell with the homeotropically aligned LC is clear and transparent. With increasing voltage and current, the electric field tries to align the long molecular axis of the LC perpendicular to the field while the ion transport through the layer has the tendency to align the LC perpendicular to the substrate plates. As a result, a pattern of repetitive striped regions called Williams domains is generated in the cell. Increasing the voltage further causes this regular pattern to be replaced by a turbulent state which strongly scatters light. This effect belongs to the class of electro-hydrodynamic effects in LCs. Electro-optic displays can be realized with the effect in the transmissive and reflective mode of operation. The driving voltages required for light scattering are in the range of several tens of volts, and the non-trivial current depends on the area of the activated segments. Historically the DSM effect was thus poorly suited for displays in battery-powered devices.

References

* G. Heilmeier, L.A. Zanoni, and L. Barton, Proc. IEEE 56, 1162 (1968) * B. Bahadur, Liquid Crystals: Applications and Uses, World Scientific, 1990 Liquid crystal displays {{scattering-stub