Using Directional Entropic Forces for Target Pattern Design.

Abstract

Designing attributes of a material’s building blocks in order to assemble them into a target structure is a major goal in materials science. In this thesis, I present three works exploring the role of geometry for self-assembly of anisotropic Brownian particles. The first work represents a systematic study of the assembly behavior of corner-truncated tetrahedra, leading to the discovery of new crystalline phases. This work also hinted to the possibility that face-to-face contacts between neighboring particles – as a consequence of what we then defined directional entropic forces – could lead to a general mechanism explaining entropy-driven assembly of convex hard polyhedra. The study of densest packings of those shapes, also performed in that work, revealed a complex landscape that opened doors for subsequent explorations of the relationship between shape and packing. The second work demonstrates how directional entropic forces can be used to predictively assemble a plethora of hard convex polyhedra into crystalline, quasicrystalline, liquid- and plastic-crystalline structures of unprecedented complexity. This work served not only as a roadmap for many experiments being now performed in the nanoscale but also as a framework from which new assembly strategies could be devised. Finally, the third work shows how the concepts elucidated in those previous works can be used for the assembly of a novel chiral crystalline structure with a priori choice of handedness. It also exemplifies the connection between geometry and isotropic interactions that can be used for assembly of complex crystalline and quasicrystalline structures. As a whole, this thesis explores the use of entropic forces as a tool for controllable assembly of stochastic building blocks and it demonstrates how harnessing geometry can have profound impact for the generation of new materials through target pattern design.