Mechanical testing of colloidal solids with millipascal stress and single-particle strain resolution

Area of Science:

• Soft Matter Physics
• Materials Science
• Colloidal Science

Background:

• Mechanical testing of colloidal solids is crucial for understanding their behavior.
• Existing methods often lack the resolution to probe deformation at the particle level.
• Directly correlating macroscopic mechanical properties with microscopic structural changes remains a challenge.

Purpose of the Study:

• To introduce traction rheoscopy, a novel technique for mechanical testing of colloidal solids.
• To enable simultaneous measurement of stress, strain, and particle-level structural changes during deformation.
• To provide insights into deformation mechanisms in soft materials.

Main Methods:

• Utilized a confocal microscope to directly measure stress and strain during deformation.
• Employed a compliant polymer gel to measure stress with single-mPa resolution.
• Monitored single-particle structural changes within the colloidal solid during deformation.
• Applied simple shear to a hard-sphere colloidal glass to demonstrate the technique.

Main Results:

• Determined the stress-strain curve and shear modulus of a colloidal glass.
• Decomposed macroscopic shear strain into elastic and plastic components.
• Calculated local strain tensors for individual particles, revealing spatial heterogeneity.
• Correlated microscopic yield criteria with macroscopic elastic-plastic behavior.

Conclusions:

• Traction rheoscopy is a sensitive tool for mechanical testing of colloidal solids.
• The technique allows for direct correlation of macroscopic mechanical response with microscopic structural dynamics.
• This method offers a unique approach to studying deformation mechanisms in diverse soft materials.