Grinding Method for Phase Transformation of Glycine

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• Glycine exhibits three polymorphs: two metastable (α, β) and one stable (γ).
• Phase transformation from α-glycine to γ-glycine is kinetically challenging.
• Understanding polymorph control is crucial for material properties and applications.

Purpose of the Study:

• To develop a simple and effective method for α-glycine to γ-glycine phase transformation.
• To investigate the role of grinding in inducing nucleation of the stable polymorph.
• To demonstrate the applicability of the grinding method in different crystallization processes.

Main Methods:

• Mechanical grinding of α-glycine crystals in an aqueous solution.
• Utilizing the Ostwald-Freundlich equation to analyze solubility changes with crystal size.
• Controlled solution concentration experiments to induce γ-glycine nucleation.
• Comparative cooling crystallization experiments with and without grinding.

Main Results:

• Grinding reduced α-glycine crystal size, increasing its saturated concentration.
• A critical solution concentration threshold (σ = 0.1) was identified for inducing γ-glycine nucleation via grinding.
• Complete α-to-γ phase transformation was achieved through grinding without additives.
• Grinding facilitated γ-glycine formation in cooling crystallization, unlike unground controls.

Conclusions:

• Physical grinding is an effective method to overcome kinetic barriers for glycine phase transformation.
• Grinding promotes nucleation of the thermodynamically stable γ-glycine polymorph.
• This technique offers a simple, additive-free route for producing stable glycine polymorphs.