Dynamic soft elasticity in monodomain nematic elastomers.

Area of Science:

• Materials Science
• Polymer Physics
• Soft Matter Physics

Background:

• Liquid crystalline elastomers (LCEs) exhibit unique mechanical properties due to the interplay between polymer elasticity and liquid crystal order.
• Understanding the dynamic-mechanical response of LCEs is crucial for their application in actuators and soft robotics.

Purpose of the Study:

• To investigate the linear dynamic-mechanical response of monodomain nematic liquid crystalline elastomers under shear.
• To explore the applicability of time-temperature superposition across the nematic-to-isotropic transition.
• To determine the frequency and time dependence of the storage modulus in different material regimes.

Main Methods:

• Dynamic-mechanical analysis (DMA) under shear deformation.
• Application of time-temperature superposition (TTS) principles.
• Analysis of Master Curves to identify power law dependencies.
• Comparison with static stress relaxation data.

Main Results:

• Master Curves were successfully obtained for the nematic liquid crystalline elastomer from the glassy state up to the nematic transition temperature (Tni).
• Time-temperature superposition failed above Tni, indicating a transition from soft-elasticity to isotropic rubber behavior.
• A power law dependence of the storage modulus (G') on frequency (G' ∝ ω^a) was established in the low-frequency region of the Master Curves.
• This power law behavior was consistent with analogous power law dependencies observed in static stress relaxation (G' ∝ t^-a).

Conclusions:

• The study demonstrates distinct dynamic-mechanical behaviors in nematic LCEs below and above the clearing point.
• Power law scaling provides a robust description of the viscoelastic response in specific temperature and frequency regimes.
• The findings offer valuable insights for designing and predicting the performance of LCEs in various applications.