Estudo computacional de sistemas polimórficos

Abstract

In this study, we analyze the structural behavior of two types of core-softened colloids: spherical and dumbbell-shaped colloids with distinct separations, ranging from almost complete overlap to no overlap. Using Molecular Dynamics simulations in the NpT ensemble, we identify that spherical colloids can exhibit well-defined crystalline structures such as a Low-Density Triangular phase, stripes, a Kagome lattice, and a High-Density Triangular phase. For dumbbell-shaped colloids, the structures are strongly affected by anisotropy. For dimers with a short intramolecular distance, we identify the Low-Density Triangular phase, an aggregate phase, and side-by-side stripes, while for cases with an intermediate distance, we identify a Low-Density Triangular phase and stripes with distinct orientation patterns. When there is no overlap between the monomers in a dumbbell, behavior similar to the symmetric spherical case is recovered. By selecting the system with an intermediate distance and exploring its phase diagram at low temperatures, due to its ability to exhibit a variety of stripe patterns, through the analysis of thermodynamic and structural changes along compression isotherms, we explore the transition between these polymorphic stripes patterns. In addition to the obtained stripe and low-density triangular solid phases, we observe a nematic fluid phase characterized by a polymer-like pattern at high temperatures and intermediate pressures. Furthermore, we demonstrate the significant role played by the new characteristic length scale, arising from the anisotropic geometry of the dimers, in the transition between stripe patterns. Notably, not only do the structural properties exhibit intriguing behavior, but diffusion and density in the nematic fluid phase also display an anomalous increase similar to that observed in water under compression. These findings can be valuable for guiding the design of materials based on nanoparticles, aiming to achieve specific mesopatterns, through the use of molecular geometry anisotropy to control self-assembly patterns.