Controlled spherulitic crystal growth from salt mixtures

Area of Science:

• Crystallization science
• Materials science
• Geochemistry

Background:

• Spherulites, polycrystalline spherical crystals, are prevalent in nature and industry.
• The crystallization dynamics and growth conditions for spherulites remain poorly understood.
• Understanding spherulite formation is crucial for applications in geology, medicine, and materials science.

Purpose of the Study:

• To elucidate the conditions for controlled spherulitic growth of sodium sulfate crystals.
• To investigate the role of divalent metal ions in inducing spherulitic morphology.
• To understand the crystallization mechanisms and solution dynamics governing spherulite formation.

Main Methods:

• Controlled evaporation of aqueous sodium sulfate solutions containing divalent metal ions at room temperature.
• Characterization of solution viscosity and supersaturation.
• Analysis of crystal nucleation, growth, and self-assembly processes using microscopy and crystallographic techniques.

Main Results:

• Divalent metal ions induce sodium sulfate spherulite formation through non-classical nucleation and nanocrystal self-assembly.
• High solution viscosity (~111 Pa·s) at supersaturation onset is critical for forming prenucleation clusters and enabling slow, diffusion-limited growth.
• Spherulites are metastable, out-of-equilibrium structures whose morphology can evolve with decreasing supersaturation and varying evaporation rates.

Conclusions:

• Controlled spherulite formation is achievable under specific solution conditions, particularly high viscosity and the presence of divalent ions.
• Non-classical crystallization pathways involving prenucleation clusters and self-assembly are key to spherulite growth.
• Findings provide insights into the fundamental mechanisms of spherulite formation and offer strategies for morphological control in crystallization processes.