Molecular Dynamics Simulations of Water Freezing in the Presence of Nanoparticles.

Understanding the freeze-thaw cycles of water in confined media, such as soil pores are necessary for proper infrastructure development in cold regions experiencing large variations in temperature as a result of fluctuating global temperatures. In this project we use the ML-mW model of water in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to try and uncover some poorly understood qualities of water freezing in the presence of nanoparticles. The coarse-grained ML-mW model was chosen over other water models, due to its freezing behavior and its low computational load which allows us to simulate many more water molecules than would otherwise be possible in an atomistic simulation. This model treats an H2O molecule as a single coarse bead and does not include computationally expensive electrostatic effects. Previous literature shows that in heterogenous ice nucleation occurs in the presence of contaminant aerosol particles such as sea salt, minerals, and volcanic dust. Many of these studies include small nanoparticles in the range of 0.3 to 1.2 nm while nanoparticles in soil are on the range of 10-20 nm. Our simulations used the Tersoff potential to simulate the interactions between the SiO2 Nanoparticle atoms and our nanoparticles are 10 nm in size, consistent with experimental literature. These results will allow us to understand the fundamental principles of ice formation in soil systems.