Liquid Crystals - Electrically Induced Alterations in Texture during Nematic Phases

Under the influence of an alternating electric field, the homogeneously orientated film is transformed into a pattern of parallel strips. These so called "Williams domains" first become unstable at the lower left-hand corner. At maximum field strength, the whole plane of vision exhibits dynamic scattering.Williams

domains develop again from the homogeneously orientated structure. Two dislocations move diagonally from the lower left-hand corner to the upper left-hand corner. From these dislocations of the strips, a knitting pattern evolves. A further increase in field strength finally leads to dynamic scattering.This general view

shows the formation of Williams domains, which are stable at low field strength. The number of disinclinations increases with increasing field strength. Formation of knitting pattern. Onset of dynamic scattering.More details can be seen at higher magnification. Williams domains with disinclinations. Formation of knitting pattern.

Start of dynamic scattering.A less stable strip pattern is formed. The strips continually move in relation to one another. This motion intensifies with increasing field strength. Finally dynamic scattering occurs.Increase in field strength leads to the formation of Williams domains.

Dynamic scattering at maximum field strength. With decreasing field strength, the strip pattern with the original spacing between strips is

resumed.Williams domains are also formed

with an increasing constant field. They decompose into a knitting pattern which is stable over a large voltage range. Finally, at maximum field strength the dynamic scattering starts at specific sites. Other parts remain static.By decreasing the field strength, a system of paired disinclinations connected

by dark strips is formed. Most of these structures dissolve rapidly. Three pairs of disinclinations remain. The disinclinations of the

pair at the lower right-hand corner attract one another. They

approach mutually with increasing speed and finally extinguish each other.Dynamic

scattering. Formation of a large number of disinclinations. On the

extreme left, four connected disinclinations approach each other - and extinguish mutually. This is a so called "healing process". The two other pairs of disinclinations remain stable.In this last experiment

the alternating field is increased continuously. - Then the voltage is reduced step-wise. The voltage jumps are accompanied by sudden changes of colour.