Designing Colloidal Open Crystals for Multifunctional Materials

多功能材料具有在单一材料中集成不同功能的能力，因此对21世纪颠覆性技术的发展有很大的需求。然而，这些材料构成了一个基本的设计挑战。开放晶体由几百纳米大小的低配位胶体粒子构成，为设计集成光子、声子和机械性能提供了一个令人兴奋的平台，从而成为多功能材料。其中一些性质及其相互作用可能是拓扑起源，为探索拓扑物理提供了丰富的平台。胶体开晶格既可以作为光子晶体，也可以作为声子晶体，这可以用于光和声管理3,4，也提供了声子-光子相互作用的机制5。这些声子晶体也可以设计成支持拓扑保护的机械状态，可以与光波耦合。虽然迄今为止基于光刻的制造技术已被用于实现某些胶体开放晶体，但这种自上而下的方法过于昂贵和耗时，特别是用于制造3D晶体结构。胶体构建块的自组装为胶体晶体提供了一种低成本、可扩展的制造途径，但这些胶体晶体往往是紧密堆积的。该项目建立在Chakrabarti小组近年来取得的显著进展的基础上，该小组建立了三块片状粒子自下而上产生胶体开放晶体7-9的通用途径，从而解决了一个长期存在的挑战。我们的计算方法考虑了设计胶体粒子的合成可行性10,11。我们利用两阶段自组装方案的多功能性来建立自下而上的路线，以实现最佳设计的胶体开放晶体。该项目的目标是建立胶状开放晶体作为集光学、声学和机械性能于一体的轻质多功能材料的平台。为此目的，目标如下：优化设计胶体开放晶体，同时管理光和声音；2. 探讨胶体开晶体的拓扑物理特性及其光子、声子和力学性质；3. 通过开发设计的三块片状粒子的自组装途径，建立自下而上的制造路线以优化设计的晶体结构。该研究项目采用了多种计算技术，这些技术由Chakrabarti小组（GlOSP和PaSSion）开发的软件包以及开放源代码和/或商业软件实现。我们使用全局优化来预测斑块颗粒的晶体结构，特别是通过三聚体，四面体或八面体形成。胶体开放晶体中的空洞允许由互穿晶格产生的显着结构多样性，这可以用于定制和优化性能。我们计算了各种晶体结构的光子和声子带结构，并使用COMSOL和其他适当的开源软件进行多物理场分析，以探索拓扑物理。我们使用先进的蒙特卡罗方法，包括在PaSSion中实现的自由能计算来建立自组装途径，以产生最佳设计的目标晶体。J. Bauer等，生物工程学报，29,1701850 （2017）M. Fruchart等。115,E3655 （2018）

Multifunctional materials are in great demand for the development of 21st-century disruptive technologies for their ability to integrate different functionalities within a single material. However, these materials pose a fundamental design challenge. Open crystals, built from low-coordinated colloidal particles in the size range of hundreds of nanometres, provide an exciting platform for integrating photonic, phononic and mechanical properties by design, and thus for multifunctional materials 1. Some of these properties and their interplay can be of topological origin, providing a rich playground for exploring topological physics 2. Colloidal open lattices can act as both photonic and phononic crystals, which can be exploited for light and sound management 3,4, also providing mechanisms for phonon-photon interactions 5. These phononic crystals can also be designed to support topologically protected mechanical states 6, which can be coupled to light waves. While lithography-based fabrication techniques have been used to realise certain colloidal open crystals to date, such top-down approaches are too expensive and time-consuming, especially for fabricating 3D crystal structures.Self-assembly of colloidal building blocks offers a low-cost, scalable fabrication route to colloidal crystals, but these tend to be close-packed. This project builds on the remarkable progress achieved in recent years by the Chakrabarti group in establishing versatile bottom-up routes for triblock patchy particles to yield colloidal open crystals 7-9, thereby addressing a long-standing challenge. Our computational approach takes into consideration synthetic feasibility of designer colloidal particles 10,11. We use the versatility of two-stage self-assembly schemes to establish bottom-up routes towards optimally designed colloidal open crystals. The aim of the project is to establish colloidal open crystals as a platform for light-weight multifunctional materials integrating optical, acoustic and mechanical properties. To this end, the objectives are as follows:1. to optimally design colloidal open crystals for simultaneous management of light and sound; 2. to explore topological physics of colloidal open crystals in connection with their photonic, phononic and mechanical properties; 3. to establish bottom-up fabrication routes to optimally designed crystal structures, by exploiting self-assembly pathways for designer triblock patchy particles. The research programme employs a variety of computational techniques, implemented in software packages developed by the Chakrabarti group (GlOSP and PaSSion) as well as in open source and/or commercially available software. We use global optimisation to predict crystal structures for patchy particles, especially formed via trimers, tetrahedra or octahedra. The voids in colloidal open crystals allow for a remarkable structural diversity arising from interpenetrating lattices, which can be exploited to tailor and optimise properties. We compute photonic and phononic band structures for various crystal structures and perform multi-physics analysis using COMSOL and other open-source software as appropriate to explore topological physics. We use advanced Monte Carlo methods including free energy calculations as implemented in PaSSion to establish self-assembly pathways to yield optimally designed target crystals.1. J. Bauer et al., Adv. Mater. 29, 1701850 (2017)2. M. Fruchart et al. 115, E3655 (2018)