Building blocks of non-Euclidean ribbons: Size-controlled self-assembly via discrete, frustrated particles

TL;DR

This paper develops a particle-based model to understand how microscopic shape and interactions of misfitting particles influence the size and structure of frustrated soft matter assemblies, especially negative-curvature ribbons.

Contribution

It introduces a discrete particle model linking microscopic properties to mesoscale assembly behavior, highlighting the role of interaction range and non-linear effects in size control.

Findings

Finite size of assemblies depends on interaction range.

Shape misfit influences strain propagation and relaxation.

Non-linear interactions lead to hierarchical structures.

Abstract

Geometric frustration offers a pathway to soft matter self-assembly with controllable finite sizes. While the understanding of frustration in soft matter assembly derives almost exclusively from continuum elastic descriptions, a current challenge is to understand the connection between microscopic physical properties of misfitting ``building blocks" and emergent assembly behavior at mesoscale. We present and analyze a particle-based description of what is arguably the best studied example for frustrated soft matter assembly, negative-curvature ribbon assembly, observed in both assemblies of chiral surfactants and shape-frustrated nanoparticles. Based on our particle model, known as {\it saddle wedge monomers}, we numerically test the connection between microscopic shape and interactions of the misfitting subunits and the emergent behavior at the supra-particle scale, specifically focusing on the propagation and relaxation of inter-particle strains, the emergent role of extrinsic shape on frustrated ribbons and the equilibrium regime of finite width selection. Beyond the intuitive role of shape misfit, we show that self-limitation is critically dependent on the finite range of cohesive interactions, with larger size finite assemblies requiring increasing short-range interparticle forces. Additionally, we demonstrate that non-linearities arising from discrete particle interactions alter self-limiting behavior due to both strain-softening in shape-flattened assembly and partial yielding of highly strained bonds, which in turn may give rise to states of hierarchical, multidomain assembly. Tracing the regimes of frustration-limited assembly to the specific microscopic features of misfitting particle shapes and interactions provides necessary guidance for translating the theory of size-programmable assembly into design of intentionally-frustrated colloidal particles.