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Untwisting of a cholesteric elastomer by a mechanical field
1Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom.
Physical Review Letters
|September 8, 2000
Summary
Mechanical strain unwinds helical director structures in cholesteric elastomers. Stretching perpendicular to the helix axis eliminates twist walls, while stretching along the axis induces conical director states, differing from liquid crystal behavior.
Area of Science:
- Materials Science
- Polymer Physics
- Soft Matter Physics
Background:
- Cholesteric elastomers exhibit unique director distributions due to helical structures.
- Mechanical fields can influence these director distributions, analogous to electric fields in liquid crystals.
- Frank elasticity plays a limited role in monodomain cholesteric elastomers unless the material is very weak.
Purpose of the Study:
- To investigate the effect of mechanical strain fields on the helical director distribution in monodomain cholesteric elastomers.
- To elucidate the mechanisms of director unwinding under different strain conditions.
- To compare the behavior of cholesteric elastomers under mechanical fields with cholesteric liquid crystals under electric fields.
Main Methods:
- Application of mechanical strain fields to monodomain cholesteric elastomers.
- Analysis of director distribution changes in response to applied strain.
- Investigation of the role of rubber elasticity and director anchoring.
Main Results:
- Mechanical strain unwinds the helical director distribution in cholesteric elastomers.
- Stretching perpendicular to the helix axis leads to a uniform unwound state by eliminating twist walls above a critical strain.
- Stretching along the helix axis results in unwinding through conical director states.
Conclusions:
- The interplay between director anchoring to the elastic matrix and the external mechanical field governs the unwinding behavior.
- Cholesteric elastomers exhibit distinct responses to mechanical strain compared to cholesteric liquid crystals under electric fields.
- Strain-induced director unwinding in cholesteric elastomers offers pathways for tunable material properties.
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