Why Seeding Works When Nucleation Barriers Vanish.

Area of Science:

• Materials Science
• Chemical Engineering
• Crystallography

Background:

• Crystallization involves nucleation and growth, with seeds typically aiding nucleation-limited processes.
• The role of seeds in accelerating crystallization when nucleation is not the limiting step is poorly understood.
• Zeolite synthesis exemplifies growth-limited crystallization where seeds accelerate the process despite low nucleation barriers.

Purpose of the Study:

• Investigate the mechanism by which seeds accelerate crystallization under growth-limited conditions.
• Clarify the role of seeds in systems with negligible homogeneous nucleation barriers.
• Determine how seeds influence the development of X-ray-detectable crystallinity.

Main Methods:

• Coarse-grained molecular dynamics simulations.
• Validation across two zeolite systems and ice crystallization.
• Analysis of crystallite orientation, coherence, and X-ray detectability.

Main Results:

• Growth-limited crystallization yields small, misoriented crystallites; coarsening dictates X-ray detectability.
• Local order, structural coherence, and X-ray detectability are kinetically decoupled.
• Seeds enforce orientational registry, enabling coherent coalescence and accelerating domain coarsening.

Conclusions:

• Seeds accelerate growth-limited crystallization by promoting spatial coherence, not primarily by reducing nucleation barriers.
• The induction period in powder X-ray diffraction reflects time to achieve long-range coherence.
• Seeds shorten the time to develop X-ray-detectable crystallinity by facilitating coherent domain growth.