Regensburg 2019 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 21: Biopolymers, biomaterials and bioinspired functional materials (joint session CPP/BP)
BP 21.4: Vortrag
Mittwoch, 3. April 2019, 16:45–17:00, H13
Inequivalence of fixed-force and fixed-extension statistical ensembles for a flexible polymer tethered to a planar substrate — •Panayotis Benetatos1 and Sandipan Dutta2 — 1Department of Physics, Kyungpook National University, Daegu, S. Korea — 2Center for Soft and Living Matter, Institute for Basic Science, Ulsan, S. Korea
Recent advances in single macromolecule experiments have sparked interest in the ensemble dependence of force-extension relations (Gibbs versus Helmholtz). The thermodynamic limit may not be attainable for such small systems, that leads to inequivalence of the fixed-force and the fixed-extension ensemble. We consider an ideal Gaussian chain described by the Edwards Hamiltonian with one end tethered to a rigid planar substrate. We analytically calculate the force-extension relation in the two ensembles and we show their inequivalence which is caused by the confinement of the polymer to half space. The inequivalence is quite remarkable for strong compressional forces. We also perform Monte-Carlo simulations of a tethered wormlike chain with contour length 20 times its persistence length which corresponds to experiments measuring the conformations of DNA tethered to a wall. The simulations confirm the ensemble inequivalence and qualitatively agree with our analytical predictions for the Gaussian model. Our analysis shows that spatial confinement due to tethering causes ensemble inequivalence, irrespective of the polymer model.