Temperature dependence of phase diagrams and dynamics in nanocrystal assembly by solvent evaporation

Abstract

We provide a systematic study of the phase diagram and dynamics for single component nanocrystals(NCs) by a combination of a self-consistent mean-field molecular theory (MOLT-CF) and moleculardynamics (MD) simulations. We first compute several thermodynamic functions (free energy, entropy,coefficient of thermal expansion and bulk modulus) as a function of temperature by both MOLT-CF andMD. While MOLT-CF correctly captures the trends with temperature, the predicted coefficients ofthermal expansion and bulk moduli display quantitative deviations from MD and experiments, which wetrace back to the mean-field treatment of attractions in MOLT-CF. We further characterize the phasediagram and calculate the dependence on temperature of the bcc to fcc transition. Our results revealthat differences in entropic and enthalpic contributions to the free energy oscillate as a function of NCseparation and are correlated to a geometric quantity: the volume of overlap between the ligand layersin different particles. In this way, we generally show that bcc is favored by enthalpy, while fcc is byentropy, in agreement with previous experimental evidence of fcc stabilization with increasingtemperature, but contrary to what is expected from simpler particle models, where bcc is alwaysentropically favored. We also show that the lowest relaxation times drastically increase in the lateststages of solvent evaporation. Overall, our results demonstrate that MOLT-CF provides an adequatequantitative model describing all phenomenology in single component NCs.