Seeding method for ice nucleation under shear

Abstract

Hydrodynamic flow can have complex and far-reaching consequences on the rate of homogeneous nucleation. We present a general formalism for calculating the nucleation rates of simply sheared systems. We have derived an extension to the conventional Classical Nucleation Theory, explicitly embodying the shear rate. Seeded molecular dynamics simulations form the backbone of our approach. The framework can be used for moderate supercooling, at which temperatures brute-force methods are practically infeasible. The competing energetic and kinetic effects of shear arise naturally from the equations. We show how the theory can be used to identify shear regimes of ice nucleation behavior for the mW water model, unifying disparate trends reported in the literature. At each temperature, we define a crossover shear rate in the limit of 1000 s−1–10 000 s−1, beyond which the nucleation rate increases steadily up to a maximum, at the optimal shear rate. For 235 K, 240 K, 255 K, and 260 K, the optimal shear rates are in the range of ≈106 s−1–107 s−1. For very high shear rates beyond 108 s−1, nucleation is strongly inhibited. Our results indicate that the optimal shear rates have a non-monotonic dependence on temperature.

Homogeneous Nucleation of Sheared Liquids: Advances and Insights from Simulations and Theory

“…(11). The height of the free energy barrier for sheared nucleation, corresponding to a critical nucleus size N * is given by [35]:…”

“…The steady-state nucleation rate, J, can be derived from Zeldovich-Frenkel equation [38,46], yielding the following familiar CNT-based expression [35]:…”

“…A crucial difference between the approach of Goswami et al [35,36] and that of Richard et al [122] is that seeded simulations must be performed for every shear rate in the case of the latter, while for the former only seeded simulations at zero shear are required. In addition, the crux of the methodology of Richard et al [122] is that the size dependent shear modulus, G ef f , is appreciably divergent from the bulk crystal shear modulus.…”

“…Figure 6: Comparison of J/J 0 for the mW model at a supercooling of 67.6 K, estimated using the formalism of Goswami et al [35,36] (open blue circles) with the MFPT results (open red triangles) of Luo et al [34]. The polynomial approximation (Eq.…”

“…Certain results indicate that shear impedes and inhibits nucleation [15,16], while others suggest that flow induces or enhances nucleation [17][18][19][20][21][22][23]. These seemingly conflicting results can be reconciled within a broader context, bolstered by experimental [24,25] and computational [26][27][28][29][30][31][32][33][34][35][36] studies which imply that the nucleation rate is non-monotonic with shear. A linear flow field tends to deform incipient clusters.…”