Temperature switchable self-propulsion activity of liquid crystalline microdroplets

Area of Science:

• Soft Matter Physics
• Materials Science
• Microfluidics

Background:

• Microswimmers offer potential for targeted delivery and sensing applications.
• Controlling microswimmer motility through external stimuli is crucial for their practical use.
• Liquid crystals (LCs) exhibit unique phase transitions exploitable for dynamic material properties.

Purpose of the Study:

• To engineer a switchable microswimmer based on liquid crystalline emulsion droplets.
• To investigate the temperature-dependent phase transitions that govern droplet motility.
• To explore the reversibility and directional memory of these microswimmers.

Main Methods:

• Fabrication of emulsion droplets using a liquid crystalline smectic phase material.
• Temperature control to induce phase transitions between smectic, nematic, and isotropic phases.
• Characterization of droplet motion, chemical fields, and hydrodynamic fields.
• Systematic mapping of motility across varying surfactant concentrations and temperatures.

Main Results:

• Liquid crystalline droplets self-propel exclusively in their nematic and isotropic phases (T ≥ 33.5 °C).
• Motility is fully reversible, with droplets exhibiting persistent motion and directional memory across heating-cooling cycles.
• Swimming is observed only at elevated temperatures and sufficient surfactant concentrations, above the smectic-nematic transition.

Conclusions:

• Liquid crystalline emulsion droplets can function as switchable microswimmers.
• Temperature serves as a reliable external trigger for controlling microswimmer activity.
• This work demonstrates the potential of LC-based microstructures for developing tunable micro-robotics.