Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 639

Full Record for Micrograph 639

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Micrograph no
639
Brief description
Twist-escaped loops in the liquid crystalline polymer MBBA
Keywords
defect Link to MATTER Glossary entry for defect, escape, liquid crystalline polymer (LCP), loop, polymer Link to MATTER Glossary entry for polymer, shear Link to MATTER Glossary entry for shear
Categories
Polymer
System
Liquid crystalline polymer
Composition
MBBA
Standard codes
Reaction
Processing
shear rate =5 s-1, sample thickness =500 microns, room temperature
Applications
The molecules in a LCP mesophase can be steered by external fields; a property used in display technology. Alignment is also exploited in high strength fibres like Kevlar and mouldable Vectra
Sample preparation
Technique
Cross-polarised light microscopy
Length bar
200 μm
Further information
Once a weak shear flow is applied on the nematic liquid, there is a sudden and strong increase in the defect density. At a certain shear rate, the equilibrium density is reached after a while through the creation and annihilation of defects. This in-situ observation enables the study of a wide range of dynamic disclination behaviours during shear, such as disclination-joining, loop-contracting, loop-stretching and loop-breaking. The loops in this image result from type 1 disclinations 'escaping' into three-dimensions by twist.
Contributor
Prof A H Windle
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
03/10/02
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales