Direct Measurements of Colloid Crystal Nucleation Barriers and Rates Comply with A Priori Classical Theory...

Area of Science:

• Physical Chemistry
• Materials Science
• Colloid Science

Background:

• Classical nucleation theory (CNT) faces challenges explaining experimental crystal nucleation rates.
• Discrepancies between CNT predictions and experimental data raise questions about its applicability.

Purpose of the Study:

• To investigate crystal nucleation using a model colloidal system that mimics molecular solutions.
• To test the validity of classical nucleation theory in a controlled environment.

Main Methods:

• Designed a suspension of attractive colloid particles with a single attractive pair potential minimum.
• Observed nucleation dynamics of quasi-two-dimensional hexagonal crystals directly.
• Utilized particle size and slow diffusion for detailed observation.

Main Results:

• Crystal nuclei assembled directly from suspended particles, aligning with classical nucleation scenarios.
• The depth of the pair potential accurately predicted equilibrium volume fractions and CNT parameters (critical nucleus size, free energy barrier).
• A diffusion-limited reaction model reproduced the nucleation rate law prefactor, with deviations observed for larger nuclei and at high supersaturations.

Conclusions:

• Classical nucleation theory effectively predicts thermodynamic and kinetic behaviors in simple crystal nucleation systems.
• Observed deviations from classical behavior (faster prefactor, spinodal-like regime) are attributed to multi-body interactions and high supersaturation effects, not failures of CNT.
• The complexity of nonclassical pathways in real systems arises from system complexity, not inherent flaws in classical theory.