Activity Induced Rigidity of Liquid Droplets.

Area of Science:

• Soft matter physics
• Colloidal science

Background:

• Drops resist deformation via interfacial tension.
• Active particles generate self-propulsion and exert forces.

Purpose of the Study:

• To investigate how active Janus particles affect droplet deformation under extensional flow.
• To quantify the increase in effective interfacial tension due to particle activity.

Main Methods:

• Deforming liquid drops containing active Janus particles using extensional flow.
• Analyzing deformation changes under varying particle concentrations and activity levels.
• Comparing experimental results with theoretical models for active particle ensembles.

Main Results:

• Encapsulating active Janus particles significantly increases a drop's resistance to deformation.
• Laser illumination activates particles, leading to a measurable increase in effective interfacial tension or Laplace pressure.
• The observed increase in effective tension closely matches a theoretical model for active particle pressure.

Conclusions:

• Active Janus particles can effectively stiffen liquid drops, mimicking enhanced interfacial tension.
• This study provides the first experimental validation of a 3D theoretical model for active particle-induced pressure.
• The findings have implications for controlling the mechanical properties of soft materials and microfluidic systems.