Defects in Crystalline Packings of Twisted Filament Bundles: II. Dislocations and Grain Boundaries

TL;DR

This paper investigates how twist-induced stresses in filament bundles cause dislocations and grain boundaries, leading to complex polycrystalline structures, using non-linear elasticity theory.

Contribution

It introduces a continuum elasticity model explaining the formation and stability of dislocations and grain boundaries in twisted filament bundles, revealing their dependence on twist and size.

Findings

Dislocations are stabilized by twist and bundle size.

Multiple dislocations form linear arrays as twist increases.

Large bundles develop polycrystalline grain boundaries.

Abstract

Twisted and rope-like assemblies of filamentous molecules are common and vital structural elements in cells and tissue of living organisms. We study the intrinsic frustration occurring in these materials between the two-dimensional organization of filaments in cross section and out-of-plane interfilament twist in bundles. Using non-linear continuum elasticity theory of columnar materials, we study the favorable coupling of twist-induced stresses to the presence of edge dislocations in the lattice packing of bundles, which leads to a restructuring of the ground-state order of these materials at intermediate twist. The stability of dislocations increases as both the degree of twist and lateral bundle size grow. We show that in ground states of large bundles, multiple dislocations pile up into linear arrays, radial grain boundaries, whose number and length grows with bundle twist, giving rise to a rich class of "polycrystalline" packings.