Topological barriers to defect nucleation generate large mechanical forces in an ordered fluid

Area of Science:

• Materials Science
• Soft Matter Physics
• Liquid Crystals

Background:

• Fluids lack molecular order, limiting mechanical strength.
• Crystalline solids possess order and strength.
• Liquid crystal films offer intermediate properties but weak elastic response at >10 nm thickness.

Purpose of the Study:

• Enhance mechanical strength of fluid films.
• Investigate viscoelastic and optomechanical properties of defect-engineered liquid crystals.
• Explore force generation and photonic bandgap shifts under confinement.

Main Methods:

• Confining cholesteric liquid crystals between curved surfaces (sphere-sphere geometry).
• Introducing topological defects (concentric dislocation loops).
• Analyzing surface forces and photonic bandgap changes during compression and retraction.

Main Results:

• Loop shrinkage and disappearance during retraction caused weak oscillatory forces.
• Topological barriers during compression created metastable states with large forces (>100 nm range).
• Metastable states induced photonic bandgap blueshifts and collapsed via stick-slip defect dynamics.

Conclusions:

• Topological defects significantly enhance the mechanical strength of cholesteric liquid crystal films.
• This defect engineering approach offers tunable viscoelastic and optomechanical responses.
• Suggests a general strategy for strengthening 1D periodic materials like cholesteric colloids.