Digital Alchemy for Materials Design: Colloids and Beyond

Abstract

Starting with the early alchemists, a holy grail of science has been to make desired materials by modifying the attributes of basic building blocks. Building blocks that show promise for assembling new complex materials can be synthesized at the nanoscale with attributes that would astonish the ancient alchemists in their versatility. However, this versatility means that making direct connection between building block attributes and bulk behavior is both necessary for rationally engineering materials, and difficult because building block attributes can be altered in many ways. Here we show how to exploit the malleability of the valence of colloidal nanoparticle "elements" to directly and quantitatively link building block attributes to bulk behavior through a statistical thermodynamic framework we term "digital alchemy". We use this framework to optimize building blocks for a given target structure, and to determine which building block attributes are most important to control for self assembly, through a set of novel thermodynamic response functions, moduli and susceptibilities. We thereby establish direct links between the attributes of colloidal building blocks and the bulk structures they form. Moreover, our results give concrete solutions to the more general conceptual challenge of optimizing emergent behaviors in nature, and can be applied to other types of matter. As examples, we apply digital alchemy to systems of truncated tetrahedra, rhombic dodecahedra, and isotropically interacting spheres that self assemble diamond, FCC, and icosahedral quasicrystal structures, Mendeleev's tabular organization of the elements[1, 2] by atomic valence [3] has served for more than 140 years as a heuristic that relates properties of the atomic elements to how they arrange in bulk structures. However, attempts to understand how properties of bulk structures relate to atomic properties predate Mendeleev and, in fact, modern science [4], and are complicated by the fact that the chemical manipulation of atoms is prohibited by the quantization of both electrical charge and angular momentum. Fortunately for Mendeleev, this quantization constrains Nature to only about 80 stable elements, and limits elemental properties and bulk behaviors so that the elements can be tabulated by valence. In fact, starting with technetium [5] in the 1930s, new atomic elements have only been produced artificially (as suggested by the etymology of the name "technetium" [6]) by α-particle bombardment, fusion, or other nuclear techniques that finally realized the ancient alchemists' goal of transmuting the elements.In contrast, an inexhaustible array of new "elements" can be synthesized as patchy particles. [7,8] However, the exploding diversity of patchy particles [8][9][10] or, more generally, colloidal "elements" means that there are now so many types to synthesize and study that synthesizing them all and determining their bulk behavior is no longer possible in practice. This fundamental impracticality means that, for colloid science to progress,...

Assembly of multi-flavored two-dimensional colloidal crystals

“…4,8–17 In principle, desired spatial symmetries of a crystal can often be obtained through intuitive design of the shape, size, and orientation of different “patches” on its constituent colloids, making this a highly attractive route for experimental realization. 4,13,14,17 However, for practical reasons not all theoretical or computational designs involving anisotropy can be easily achieved in an experimental setting 4,14 and additional factors, such as structure directing agents, may be required to obtain the desired structure. 18–20 A seemingly simpler alternative is to construct isotropic interactions that can achieve the same end goals.…”

Nanoparticle Assembly:A Perspective and some Unanswered Questions

“…(ii) Perhaps the more ambitious means of such a priori design is to use reverse modeling tools, e.g. using genetic algorithm [31][32][33][34] , to design the building blocks that can assemble into a structure with desired function. The current implementation of such ideas has been largely limited to the prediction of colloidal building blocks that assemble into desired ordered structures -in particular, this has been applied to the assembly of colloids grafted with DNA strands, where two colloidal sub-populations have complementary single strands.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Colloidal NCs can also selfassemble into three-dimensionally ordered colloidal superparticles [131]. The geometry and properties of these superstructures can be tailored by the size, shape, composition and surface chemistry of the NC or hetero-NC building blocks [129][130][131][132][133][134][135][136][137][138]. In particular, surface ligands have been shown to have a dramatic impact on the directionality of the self-organization process [135,[139][140][141][142][143], leading in some cases to atomically aligned NC superlattices [135,139,143].…”