Issue 14, 2022

Combing a double helix

Abstract

Combing hair involves brushing away the topological tangles in a collective curl, defined as a bundle of interacting elastic filaments. Using a combination of experiment and computation, we study this problem that naturally links topology, geometry and mechanics. Observations show that the dominant interactions in hair are those of a two-body nature, corresponding to a braided homochiral double helix. This minimal model allows us to study the detangling of an elastic double helix driven by a single stiff tine that moves along it and leaves two untangled filaments in its wake. Our results quantify how the mechanics of detangling correlates with the dynamics of a topological quantity, the link density, that propagates ahead of the tine and flows out the free end as a link current. This in turn provides a measure of the maximum characteristic length of a single combing stroke in the many-body problem on a head of hair, producing an optimal combing strategy that balances trade-offs between comfort, efficiency and speed of combing in hair curls of varying geometrical and topological complexity.

Graphical abstract: Combing a double helix

Supplementary files

Article information

Article type
Paper
Submitted
26 Oct 2021
Accepted
18 Feb 2022
First published
22 Mar 2022

Soft Matter, 2022,18, 2767-2775

Combing a double helix

T. B. Plumb-Reyes, N. Charles and L. Mahadevan, Soft Matter, 2022, 18, 2767 DOI: 10.1039/D1SM01533H

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