Comment on "Solvent-Induced Negative Energetic Elasticity in a Lattice Polymer Chain''

L. K. R. Duarte; L. G. Rizzi

paper

Comment on "Solvent-Induced Negative Energetic Elasticity in a Lattice Polymer Chain''

arXiv:2503.22614

Abstract

In a recent Letter, Shirai and Sakumichi [Phys. Rev. Lett. 130, 148101 (2023), arXiv:2202.12483] presented a study focusing on the origin of a temperature-dependent negative contribution $G_{U} (T)$ to the elastic modulus $G (T)$ of hydrogels [Yoshikawa et al., Phys. Rev. X 11, 011045 (2021)]. The authors support their findings through an energy-related stiffness $k_{U} (r, T)$ obtained from a single chain, with $r$ being the end-to-end distance of a random walk on a 3D lattice. It is argued that the parameter $ε$ related to polymer-solvent interactions is positive, so the energy $E_{s}$ of an elongated state should be smaller than the energy $E_{b}$ of a more compact state. We believe that the analogy between $G_{U} (T)$ and $k_{U} (r, T)$ might have misled their claim that $G_{U} (T) < 0$ when $ε > 0$ .

Comment on arXiv:2202.12483, Shirai and Sakumichi [Phys. Rev. Lett. 130, 148101 (2023), DOI: 10.1103/PhysRevLett.130.148101], 1 page, 1 figure, correspondence with PRL's editor (5 pages)