Triple junction at the triple point resolved on the individual particle level

TL;DR

This study visualizes the triple junction of three phases at the particle level in a colloidal system, revealing broad interfaces and low interfacial energy, with implications for understanding phase coexistence.

Contribution

It provides the first direct particle-level visualization of the triple junction in a colloidal system and quantifies interfacial energies near the triple point.

Findings

Deep liquid groove at the triple junction.

Broad incommensurate solid-solid interface.

Low interfacial energy between phases.

Abstract

At the triple point of a repulsive screened Coulomb system, a face-centered-cubic (fcc) crystal, a body-centered-cubic (bcc) crystal and a fluid phase coexist. At their intersection, these three phases form a liquid groove, the triple junction. Using confocal microscopy, we resolve the triple junction on a single particle level in a model system of charged PMMA colloids in a nonpolar solvent. The groove is found to be extremely deep and the incommensurate solid-solid interface to be very broad. Thermal fluctuations hence appear to dominate the solid-solid interface. This indicates a very low interfacial energy. The fcc-bcc interfacial energy is quantitatively determined based on Young's equation and, indeed, it is only about 1.3 times higher than the fcc-fluid interfacial energy close to the triple point.