Crystallizability

Crystallizability is the ability of a substance to form a crystalline solid under a given set of conditions. It reflects whether a material can organize into a periodic lattice from a solution, melt, or gas phase, and it depends on both thermodynamic driving forces and kinetic barriers. Crystallizability is not fixed for a substance; it varies with temperature, pressure, solvent, concentration, impurities, and the rate at which the system is cooled or concentrated.

Key factors include supersaturation as the thermodynamic driving force, nucleation barriers, and crystal growth rates. Nucleation can be primary or secondary, and its induction time and occurrence determine when crystallization starts. Solvent choice, pH, and impurities influence solubility, interfacial energies, and lattice compatibility, thereby promoting or inhibiting crystallization. Polymorphism and solvates add complexity, because several crystalline forms may be possible and not all are equally stable under the same conditions.

Assessment and application span pharmaceuticals, polymers, and biochemistry. In drugs, crystallizability influences solid-form selection, processing, and bioavailability. In polymers, it governs crystallinity and properties such as stiffness and barrier performance. In protein crystallography, crystallizability determines the feasibility of structure determination. Practical evaluation uses metastable zone width, induction time, and crystallization kinetics, together with analytical tools such as X-ray diffraction, differential scanning calorimetry, and polarized-light microscopy.

Examples include straightforward crystallization of sugars like sucrose from supersaturated solutions, as well as polymorphic forms of fats and several organic compounds. Proteins often require careful control of conditions to yield crystals suitable for diffraction. Overall, crystallizability describes the balance between thermodynamic stability of a crystalline phase and the kinetic accessibility of that phase under the chosen process.