4.7 Article

Mechanisms of Nucleation and Solid-Solid-Phase Transitions in Triblock Janus Assemblies

Journal

JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Volume 17, Issue 3, Pages 1742-1754

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.0c01080

Keywords

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Funding

  1. Deutsche Forschungsgemeinschaft (DFG) [MU1412/25-2, SFB-TRR146]

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The study employed a model to simulate nucleation and solid-solid phase transitions of triblock Janus particles, revealing a two-step mechanism. The distinction between unbiased and biased simulations lies in the generation of multiple nuclei and their growth processes.
A model, including the chemical details of core nanoparticles as well as explicit surface charges and hydrophobic patches, of triblock Janus particles is employed to simulate nucleation and solid-solid phase transitions in two-dimensional layers. An explicit solvent and a substrate are included in the model, and hydrodynamic and many-body interactions were taken into account within many-body dissipative particle dynamics simulation. In order not to impose a mechanism a priori, we performed free (unbiased) simulations, leaving the system the freedom to choose its own pathways. In agreement with the experiment and previous biased simulations, a two-step mechanism for the nucleation of a kagome lattice from solution was detected. However, a distinct feature of the present unbiased versus biased simulations is that multiple nuclei emerge from the solution; upon their growth, the aligned and misaligned facets at the grain boundaries are introduced into the system. The liquid-like particles trapped between the neighboring nuclei connect them together. A mismatch in the symmetry planes of neighboring nuclei hinders the growth of less stable (smaller) nuclei. Unification of such nuclei at the grain boundaries of misaligned facets obeys a two-step mechanism: melting of the smaller nuclei, followed by subsequent nucleation of liquid-like particles at the interface of bigger neighboring nuclei. Besides, multiple postcritical nuclei are formed in the simulation box; the growth of some of which stops due to introduction of a strain in the system. Such an incomplete nucleation/growth mechanism is in complete agreement with the recent experiments. The solid-solid (hexagonal-to-kagome) phase transition, at weak superheatings, obeys a two-step mechanism: a slower step (formation of a liquid droplet), followed by a faster step (nucleation of kagome from the liquid droplet).

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