Triple Junction at the Triple Point Resolved on the Individual Particle Level

Area of Science:

• Colloid science
• Soft matter physics
• Crystallization phenomena

Background:

• Repulsive screened Coulomb systems exhibit complex phase behavior.
• The coexistence of multiple phases (fcc, bcc, fluid) occurs at a specific triple point.
• The intersection of these three phases forms a triple junction, a liquid groove.

Purpose of the Study:

• To resolve the triple junction on a single-particle level.
• To investigate the structure and properties of the solid-solid interface within the triple junction.
• To quantitatively determine the fcc-bcc interfacial energy.

Main Methods:

• Utilized confocal microscopy for high-resolution imaging.
• Employed a model system of charged polymethyl methacrylate (PMMA) colloids in a nonpolar solvent.
• Applied Young's equation to calculate interfacial energy.

Main Results:

• Observed an extremely deep liquid groove forming the triple junction.
• Found a very broad, incommensurate solid-solid interface.
• Demonstrated that thermal fluctuations dominate the solid-solid interface, indicating low interfacial energy.
• Quantified the fcc-bcc interfacial energy, finding it approximately 1.3 times the fcc-fluid interfacial energy near the triple point.

Conclusions:

• The study provides a single-particle-level understanding of triple junctions in colloidal systems.
• The broad solid-solid interface and low interfacial energy are attributed to dominant thermal fluctuations.
• Results offer insights into phase transitions and interfacial phenomena in soft matter.