Tiling a tubule: How increasing complexity improves the yield of self-limited assembly

TL;DR

This paper demonstrates that increasing the complexity of subunit types in self-assembling tubules significantly enhances assembly specificity and yield, by reducing off-target structures through strategic tiling rules.

Contribution

It introduces a method of using multiple subunit species and tiling rules to improve the selectivity and yield of self-assembled tubules, extending the design principles for complex colloidal structures.

Findings

Multiple subunit species dramatically improve assembly selectivity.

Finite bending rigidity causes off-target structures in single-species systems.

Minimum number of subunit types needed for near-perfect yield is identified.

Abstract

The ability to design and synthesize ever more complicated colloidal particles opens the possibility of self-assembling a zoo of complex structures, including those with one or more self-limited length scales. An undesirable feature of systems with self-limited length scales is that thermal fluctuations can lead to the assembly of nearby, off-target states. We investigate strategies for limiting off-target assembly by using multiple types of subunits. Using simulations and energetics calculations, we explore this concept by considering the assembly of tubules built from triangular subunits that bind edge to edge. While in principle, a single type of triangle can assemble into tubules with a monodisperse width distribution, in practice, the finite bending rigidity of the binding sites leads to the formation of off-target structures. To increase the assembly specificity, we introduce tiling rules for assembling tubules from multiple species of triangles. We show that the selectivity of the target structure can be dramatically improved by using multiple species of subunits, and provide a prescription for choosing the minimum number of subunit species required for near-perfect yield. Our approach of increasing the system's complexity to reduce the accessibility of neighboring structures should be generalizable to other systems beyond the self-assembly of tubules.