Deformation of cholesteric elastomers by uniaxial stress along the helix axis |
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Authors: | W Stille |
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Institution: | 1.Physikalisches Institut,Albert-Ludwigs-Universit?t,Freiburg,Germany |
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Abstract: | The deformation of cholesteric elastomers by mechanical stress applied parallel to the helix axis is studied by calculation
of the free-energy density. The Frank-elasticity contribution is taken into account. A chiral solvent, present at cross-linking
time, is in general considered to be replaced after cross-linking by a solvent with different chirality. Two special cases
considered are zero and unchanged solvent chirality, the first known as that of imprinted cholesteric elastomers, the latter
equivalent to intrinsic cholesteric elastomers with chemically attached chiral groups. Depending on material parameters and
imposed strain, the director can show a tilt towards the helix axis up to the maximum tilt, corresponding to a nematic state.
In case of intrinsic elastomers with low conformation anisotropy, direct transitions from untilted to nematic states can be
induced by straining. The helix structure of the director field is coarsened with an average wave number different to that
of the information inscribed in the network at cross-linking time, if this lowers the average free-energy density. Switching
between different states can be achieved with electric fields of reasonable values applied parallel to the helix axis. Spectra
of the reflection of polarized light are calculated. |
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Keywords: | PACS" target="_blank">PACS 83 80 Va Elastomeric polymers 61 30 -v Liquid crystals 42 70 Qs Photonic bandgap materials |
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