Writhing and hockling instabilities in twisted elastic fibers

TL;DR

This paper investigates the formation and energy dynamics of buckling, hockles, and plectonemes in twisted elastic fibers through micron-scale experiments, revealing hysteresis and energy release mechanisms.

Contribution

It introduces an experimental approach to study the energy stored and released by twisted elastic fibers, drawing analogies with DNA and protein folding.

Findings

Hysteresis loops reveal energy storage and release.

Formation of hockles and plectonemes depends on twisting and pulling.

Experimental results inform understanding of elastic fiber mechanics.

Abstract

The buckling and twisting of slender, elastic fibers is a deep and well-studied field. A slender elastic rod that is twisted with respect to a fixed end will spontaneously form a loop, or hockle, to relieve the torsional stress that builds. Further twisting results in the formation of plectonemes -- a helical excursion in the fiber that extends with additional twisting. Here we use an idealized, micron-scale experiment to investigate the energy stored, and subsequently released, by hockles and plectonemes as they are pulled apart, in analogy with force spectroscopy studies of DNA and protein folding. Hysteresis loops in the snapping and unsnapping inform the stored energy in the twisted fiber structures.