Stiffening Liquid Crystal Elastomers with Liquid Crystal Inclusions

Area of Science:

• Materials Science
• Polymer Science
• Soft Robotics

Background:

• Liquid crystal elastomers (LCEs) offer large, programmable shape changes, ideal for soft robots.
• Existing methods to enhance LCE stiffness often compromise molecular order and thermal strain.
• A need exists for improved LCE mechanical properties without sacrificing key performance characteristics.

Purpose of the Study:

• To enhance the stiffness and toughness of LCEs.
• To investigate the effect of low molecular weight liquid crystals (LMWLCs) on LCE mechanical properties.
• To maintain molecular order and thermal strain while improving stiffness.

Main Methods:

• Incorporation of LMWLCs into LCEs to create LC-LCEs.
• Thermomechanical analysis to evaluate mechanical properties and phase transitions.
• X-ray analysis to confirm structural changes and molecular order.

Main Results:

• LC-LCEs exhibit enhanced linear elasticity before reaching a soft elastic plateau.
• An additional mesophase, evolving to short-range smectic order, was observed in polydomain LC-LCEs.
• Monodomain LC-LCEs showed 6.5- to 9.0-fold stiffness enhancement with improved molecular order and thermal strain.
• LC-LCEs demonstrated doubled work densities and up to 25% active thermal stroke under significant loads.

Conclusions:

• LMWLC inclusion is a simple and effective strategy to significantly improve LCE mechanical properties.
• The enhanced properties arise from the interplay of LMWLC phase separation and strain-enhanced smectic ordering.
• This approach offers a robust method for developing advanced LCE materials for soft robotics and other applications.