Liquid Crystals - Electrically Induced Alterations in Texture during Nematic Phases

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Formal Metadata

Title
Liquid Crystals - Electrically Induced Alterations in Texture during Nematic Phases
Alternative Title
Flüssige Kristalle - Elektrisch induzierte Texturänderungen bei nematischen Phasen
Author
Sackmann, Erich
License
CC Attribution - NonCommercial - NoDerivatives 3.0 Germany:
You are free to use, copy, distribute and transmit the work or content in unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor.
DOI
IWF Signature
E 2422
Publisher
IWF (Göttingen)
Release Date
1977
Language
English
Producer
IWF
Production Year
1974

Technical Metadata

IWF Technical Data
Film, 16 mm, LT, 76 m ; F, 7 min

Content Metadata

Subject Area
Abstract
Transition at three threshold voltages (transition field strengths) to a) a band-like domain pattern of high symmetry (Williams-domains), b) a still regular domain structure of lower symmetry (decomposition of the bands), and c) a completely turbulent state (dynamic scattering regime). Interaction between disclination lines (defects in molecular orientation) after switching off the electric field.
Keywords
disclination lines
ferroelectric domains
domains, ferroelectric
liquid crystals
crystals / liquid crystals
nematic phase
texture, nematic
Weiss domain
Williams domains

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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.
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