Unusual winding of helices under tension

Abstract

An unusual overwinding and a subsequently unwinding behavior of helix of filament with twisted microstructures under stretch is analyzed from the nonlinear variation of material chirality (i.e., chirality in material properties), motivated by recent single-molecule experiments for B-DNA. We establish a refined Cosserat rod model, which reproduces the deformation behaviors of filament incorporating its microscopic chirality. The helix of filament with twisted microstructures is found to exhibit a DNA-like nonlinear variation of material chirality under large elongation. The multiscale interactions between microscopic chirality of twisted microstructures and macroscopic chirality of helix determine the nonlinear coupling behaviors of hierarchically chiral structured materials. These results provide a fundamental principle for understanding the functions and mechanisms of chiral materials.