Prestipino Santi, Pini Davide, Costa Dino, Malescio Gianpietro, Munaò Gianmarco
Dipartimento di Scienze Matematiche e Informatiche, Scienze Fisiche e Scienze della Terra, Università degli Studi di Messina, Viale F. Stagno d'Alcontres 31, 98166 Messina, Italy.
Dipartimento di Fisica "A. Pontremoli," Università di Milano, Via Celoria 16, 20133 Milano, Italy.
J Chem Phys. 2023 Nov 28;159(20). doi: 10.1063/5.0177209.
In a binary mixture, stripes refer to a one-dimensional periodicity of the composition, namely, a regular alternation of layers filled with particles of mostly one species. We have recently introduced [Munaò et al., Phys. Chem. Chem. Phys. 25, 16227 (2023)] a model that possibly provides the simplest binary mixture endowed with stripe order. The model consists of two species of identical hard spheres with equal concentration, which mutually interact through a square-well potential. In that paper, we have numerically shown that stripes are present in both liquid and solid phases when the attraction range is rather long. Here, we study the phase behavior of the model in terms of a density functional theory capable to account for the existence of stripes in the dense mixture. Our theory is accurate in reproducing the phases of the model, at least insofar as the composition inhomogeneities occur on length scales quite larger than the particle size. Then, using Monte Carlo simulations, we prove the existence of solid stripes even when the square well is much thinner than the particle diameter, making our model more similar to a real colloidal mixture. Finally, when the width of the attractive well is equal to the particle diameter, we observe a different and more complex form of compositional order in the solid, where each species of particle forms a regular porous matrix holding in its holes the other species, witnessing a surprising variety of emergent behaviors for a very basic model of interaction.
在二元混合物中，条纹是指组成的一维周期性，即主要由一种粒子填充的层的规则交替。我们最近提出了一种模型[穆瑙奥等人，《物理化学化学物理》25，16227(2023)]，它可能是具有条纹序的最简单的二元混合物。该模型由两种浓度相等的相同硬球组成，它们通过方阱势相互作用。在那篇论文中，我们通过数值计算表明，当吸引范围相当长时，液相和固相中都存在条纹。在这里，我们用一种能够解释稠密混合物中条纹存在的密度泛函理论来研究该模型的相行为。我们的理论在重现模型的相方面是准确的，至少在组成不均匀性出现在比粒子尺寸大得多的长度尺度上时是如此。然后，通过蒙特卡罗模拟，我们证明即使方阱比粒子直径薄得多，固体条纹仍然存在，这使得我们的模型更类似于真实的胶体混合物。最后，当吸引阱的宽度等于粒子直径时，我们在固体中观察到一种不同的、更复杂的组成序形式，其中每种粒子形成一个规则的多孔基质，在其孔中容纳另一种粒子，这见证了一个非常基本的相互作用模型中令人惊讶的各种涌现行为。
