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.
Université de Lorraine, LCP-A2MC, UR 3469, Metz F-57078, France.
Phys Chem Chem Phys. 2023 Jun 21;25(24):16227-16237. doi: 10.1039/d3cp01026k.
Self-assembly of colloidal particles into striped phases is at once a process of relevant technological interest-just think about the possibility to realise photonic crystals with a dielectric structure modulated along a specific direction-and a challenging task, since striped patterns emerge in a variety of conditions, suggesting that the connection between the onset of stripes and the shape of the intermolecular potential is yet to be fully unravelled. Hereby, we devise an elementary mechanism for the formation of stripes in a basic model consisting of a symmetric binary mixture of hard spheres that interact a square-well cross attraction. Such a model would mimic a colloid in which the interspecies affinity is of longer range and significantly stronger than the intraspecies interaction. For attraction ranges shorter enough than the particle size the mixture behaves like a compositionally-disordered simple fluid. Instead, for wider square-wells, we document by numerical simulations the existence of striped patterns in the solid phase, where layers of particles of one species are interspersed with layers of the other species; increasing the attraction range stabilises the stripes further, in that they also appear in the bulk liquid and become thicker in the crystal. Our results lead to the counterintuitive conclusion that a flat and sufficiently long-ranged unlike attraction promotes the aggregation of like particles into stripes. This finding opens a novel way for the synthesis of colloidal particles with interactions tailored at the development of stripe-modulated structures.
胶体粒子自组装成条纹相既是一个具有重要技术意义的过程——试想一下，用沿特定方向调制的介电结构来实现光子晶体的可能性——也是一个具有挑战性的任务，因为在各种条件下都会出现条纹图案，这表明条纹的出现与分子间势的形状之间的联系尚未完全解开。为此，我们设计了一种基本模型中条纹形成的基本机制，该模型由硬球组成的对称二元混合物组成，它们之间存在方阱交叉吸引力。这种模型可以模拟一种胶体，其中种间亲和力的作用范围更长，强度也比种内相互作用强得多。对于吸引力范围短于粒子尺寸的情况，混合物的行为类似于组成无序的简单流体。相反，对于更宽的方阱，我们通过数值模拟证明了在固体相中存在条纹图案，其中一种粒子的层与另一种粒子的层相互交错；增加吸引力范围会进一步稳定条纹，因为它们也会出现在体相液体中，并在晶体中变厚。我们的结果得出了一个反直觉的结论，即平坦且足够长程的不同吸引力促进了相似粒子聚集形成条纹。这一发现为合成具有定制相互作用的胶体颗粒开辟了一条新途径，以开发条纹调制结构。
