Alladi Ramakrishnan Hall

Exploring the role of impurities on nucleation in two dimensional Ising lattice-gas model of solute precipitation

Dipanjan Mandal

University of Warwick, UK

Nucleation phenomena are ubiquitous in nature and the
impurities are present in almost every real and experimental system
showing nucleation. Impurities play a diverse role influencing the
nucleation properties of the system. It could boost up or slow down
the nucleation rate acting as nucleant, surfactant or blocking
particles from getting attached to the growing nucleus. Simple models
like Ising and Potts lattice-gas model can be used to get insights
about the nucleation properties of such complicated systems.

In this talk I am going to explore the role of randomly positioned
static and dynamic impurities on nucleation in the 2D Ising
lattice-gas model of solute precipitation. Impurity-solute and
impurity-solvent interaction energies are varied whilst keeping other
interaction energies fixed. We have shown that both the free energy
barrier height and critical nucleus size monotonically decreases with
increasing the impurity density for the static case when interaction
energies are neutral. In the case of dynamic impurities we explore a
broad range of both symmetric and anti-symmetric interactions with
impurities and map the regime for which the impurities act as a
surfactant, decreasing the surface free energy of the nucleating
phase. We also characterise different nucleation regimes observed at
different values of the interaction energy, which include regimes
where impurities play the role of surfactant, inactive-spectator,
nucleant or heterogeneous nucleation sites with clustering impurities.

References:
[1] D. Mandal and D. Quigley, Soft Matter, 2021, 17, 8642-8650.
[2] D. Mandal and D. Quigley, arXiv:2312.08342.