Heterogeneous and homogeneous nucleation compared: rapid nucleation on microscopic impurities

Area of Science:

• Computational physics
• Materials science
• Chemical engineering

Background:

• Nucleation is a critical process in phase transitions, influencing material properties and formation.
• Homogeneous nucleation occurs spontaneously, while heterogeneous nucleation is facilitated by surfaces or impurities.
• Understanding nucleation rates is essential for controlling crystallization and material synthesis.

Purpose of the Study:

• To computationally determine and compare the rates of homogeneous and heterogeneous nucleation.
• To investigate the impact of microscopic impurity size on heterogeneous nucleation rates.
• To assess the relevance of homogeneous nucleation in the presence of impurities.

Main Methods:

• Utilized computer simulations based on the two-dimensional Ising model.
• Calculated nucleation rates for both homogeneous and heterogeneous pathways.
• Systematically varied the size of microscopic impurities (fixed spins).

Main Results:

• Heterogeneous nucleation on a single fixed spin impurity was over four orders of magnitude faster than homogeneous nucleation.
• Heterogeneous nucleation rates increased approximately fivefold for each additional fixed spin in the impurity.
• Homogeneous nucleation becomes negligible when even small microscopic impurities are present.

Conclusions:

• Microscopic impurities, even as small as single molecules, dramatically accelerate heterogeneous nucleation.
• Heterogeneous nucleation dominates over homogeneous nucleation in systems with impurities.
• These findings have implications for understanding and controlling phase transitions in various fluid systems.