Effect of substrate mismatch, orientation, and flexibility on heterogeneous ice nucleation

TL;DR

This study uses molecular simulations to investigate how substrate lattice mismatch, orientation, and flexibility influence heterogeneous ice nucleation, revealing that structural mismatch reduces nucleation temperature, orientation has minimal effect, and flexibility enhances nucleation efficiency.

Contribution

It isolates the effect of structural mismatch on ice nucleation and compares the influence of substrate orientation and flexibility using molecular simulations.

Findings

A 1% increase in mismatch decreases nucleation temperature by ~4 K.

Different ice orientations show similar nucleation abilities.

Flexible substrates are more effective in nucleating ice due to structural adaptation.

Abstract

Heterogeneous nucleation is the main path to ice formation on Earth. The ice nucleating ability of a certain substrate is mainly determined by both molecular interactions and the structural mismatch between the ice and the substrate lattices. We focus on the latter factor using molecular simulations of the mW model. Quantifying the effect of structural mismatch alone is challenging due to its coupling with molecular interactions. To disentangle both factors, we use a substrate composed of water molecules in such a way that any variation on the nucleation temperature can be exclusively ascribed to the structural mismatch. We find that a one per cent increase of structural mismatch leads to a decrease of approximately 4 K in the nucleation temperature. We also analyse the effect of the orientation of the substrate with respect to the liquid. The three main ice orientations (basal, primary prism and secondary prism) have a similar ice nucleating ability. We finally asses the effect of lattice flexibility by comparing substrates where molecules are immobile with others where a certain freedom to fluctuate around the lattice positions is allowed. Interestingly, we find that the latter type of substrate is more efficient in nucleating ice because it can adapt its structure to that of ice.