Effects of shear flow on phase nucleation and crystallization

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Materials Science

Background:

• Classical nucleation theory explains phase transitions in static systems.
• Nucleation in liquids is often influenced by hydrodynamic flow, with unclear effects on the process.
• Existing theories lack a comprehensive understanding of shear's impact on nucleation.

Purpose of the Study:

• To develop a classical nucleation theory for sheared systems.
• To derive a closed-form expression for nucleation rate under shear.
• To elucidate the competing effects of flow on molecular transport and nucleus deformation.

Main Methods:

• Developed a classical nucleation theory from the Becker-Doering master kinetic equation.
• Analytically derived a closed-form expression for the nucleation rate.
• Incorporated flow-mediated molecular transport and mechanical deformation of the nucleus.

Main Results:

• Identified a competition between flow-induced molecular transport (accelerating nucleation) and nucleus straining (slowing nucleation).
• Demonstrated a non-monotonic dependence of nucleation rate on shear rate.
• Predicted an optimal shear rate that increases nucleation rate by an order of magnitude.

Conclusions:

• Hydrodynamic shear can significantly enhance nucleation rates in liquids.
• The interplay between molecular transport and nucleus deformation dictates the overall effect of shear.
• The developed theory provides a framework for understanding and predicting shear-enhanced nucleation.