Forced extension of a wormlike chain in the Gibbs and Helmholtz ensembles

Nigel T Andersen; Jeff Z Y Chen

doi:10.1063/5.0191727

Forced extension of a wormlike chain in the Gibbs and Helmholtz ensembles

J Chem Phys. 2024 Feb 28;160(8):084903. doi: 10.1063/5.0191727.

Authors

Nigel T Andersen¹, Jeff Z Y Chen¹

Affiliation

¹ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.

PMID: 38385518
DOI: 10.1063/5.0191727

Abstract

A semiflexible polymer can be stretched by either applying a force to it or by fixing the positions of its endpoints. The two approaches generally yield different results and correspond to experiments performed in either the Gibbs or Helmholtz statistical ensembles. Here, we derive the Helmholtz force-extension relationship for the commonly used wormlike-chain model in the strongly stretched regime. By analyzing it in comparison with the Gibbs ensemble result, we show that equivalence between the two relationships is achieved only in the long-chain thermodynamic limit.