(490c) Statistical Mechanics of Crystallization and Vitrification | AIChE

(490c) Statistical Mechanics of Crystallization and Vitrification


Hasyim, M. R. - Presenter, University of California - Berkeley
Mandadapu, K. K., University of California, Berkeley
All glass formers must compete with crystallization to vitrify and obtain the amorphous solid. An emergent property of this competition is the non-monotonic shape of crystallization timescales, as indicated by their time-temperature-transformation (TTT) diagrams. We construct the Arrow-Potts model as a coarse-grained model to explore this competition and guide the construction of a suitable theory for crystallization. Using Monte Carlo (MC) simulations, the model not only reproduces experimentally observed TTT diagrams, but it also showcases two regimes for crystallization. At high temperatures, the system crystallizes by the nucleation of compact and fluctuating clusters which results into foam-like polycrystalline microstructures. At low temperatures, crystals grow into fractal ramified clusters filled with amorphous voids which are indicative of the growing presence of vitrification. A theory for crystallization is developed using Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory as a unifying framework to combine the field theory of nucleation and a random walk theory for the facilitated relaxation events governing crystal growth inside the liquid. The theory showcases not only how scaling exponents are encoded within crystallization timescales but also how crucial these exponents are to accurately account the observed TTT diagram of the model at the temperature regimes of interest.