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Liquid crystalline elastomers: dynamics and relaxation of microstructure
E M Terentjev1, A Hotta, S M Clarke
1Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
Summary
Nematic elastomers exhibit unusual dynamic mechanical responses, including significant modulus reduction and increased dissipation at low frequencies. These findings align with power-law behaviors observed in both dynamic and static mechanical tests.
Area of Science:
- Materials Science
- Polymer Physics
- Rheology
Background:
- Nematic elastomers display unique mechanical properties influenced by strain and nematic director orientation.
- The dynamic mechanical response of these materials, especially across phase transitions, is not fully understood.
Purpose of the Study:
- To investigate the linear dynamic mechanical response of monodomain nematic elastomers under shear.
- To analyze time-temperature superposition effects on dynamic data near phase transitions.
Main Methods:
- Dynamic mechanical analysis (DMA) under shear.
- Time-temperature superposition (TTS) analysis of dynamical data.
- Comparison with static stress relaxation experiments.
Main Results:
- Observed a dramatic reduction in rubber plateau modulus at low frequencies.
- Noted a significant rise in internal dissipation in geometries supporting dynamic soft elasticity.
- Found power-law frequency dependence of storage modulus (G' ∝ ω⁻ᵃ) consistent with static stress relaxation (G' ∝ t⁻ᵃ).
Conclusions:
- Dynamic mechanical response of nematic elastomers is highly unusual, mirroring static behaviors.
- Power-law relationships govern both dynamic and static responses in specific regimes.
- Soft elasticity regimes are characterized by modulus reduction and increased dissipation.