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Urea homogeneous nucleation mechanism is solvent dependent
Matteo Salvalaglio1, Marco Mazzotti, Michele Parrinello
1ETH Zurich, Institute of Process Engineering, Soneggstrasse 3, CH-8092 Zurich, Switzerland. salvalaglio@ipe.mavt.ethz.ch.
Faraday Discussions
|April 14, 2015
Summary
Solvent choice significantly impacts urea crystallization, influencing whether nucleation occurs in one or two steps. This study used molecular dynamics to reveal solvent-dependent nucleation mechanisms and minor effects on polymorphism.
Area of Science:
- Crystallization Science
- Materials Chemistry
- Computational Chemistry
Background:
- The mother phase composition is critical in crystallization, influencing nucleation and growth kinetics.
- Understanding solvent effects on nucleation mechanisms is essential for controlling crystal formation.
Purpose of the Study:
- To investigate the influence of different solvents on urea nucleation mechanisms.
- To determine if solvents affect urea's early-stage polymorphic transitions.
- To analyze the impact of finite system sizes on nucleation free energy surfaces.
Main Methods:
- Enhanced sampling molecular dynamics simulations were employed.
- The nucleation pathways of urea in various solvents were analyzed.
- Finite size effects on free energy calculations were systematically evaluated.
Main Results:
- Urea nucleation proceeds via a single-step mechanism in methanol and ethanol.
- A two-step nucleation mechanism is favored in acetonitrile.
- Solvents exhibit a minimal influence on early-stage urea polymorphic transitions.
Conclusions:
- Solvent choice dictates the nucleation pathway (single-step vs. two-step) for urea crystallization.
- Early polymorphic transitions of urea are largely insensitive to solvent effects.
- Simulation setup and finite size effects are important considerations for accurate free energy calculations in nucleation studies.
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