# O'Connor, Alvarez, and Robbins Reply to Xu et al. (arXiv:1808.05390)

## TL;DR

This paper clarifies and corrects previous misunderstandings about the application of entropic stress expressions in polymer flow, emphasizing that deviations at extreme extension rates are expected and do not undermine prior conclusions.

## Contribution

The authors clarify the proper application of entropic stress expressions and address misconceptions in previous critiques, reaffirming their original findings.

## Key findings

- Deviations at extreme extension rates are expected and not indicative of errors.
- Misapplication of entropic stress expressions leads to minor discrepancies.
- The original conclusions remain valid despite the critique.

## Abstract

The preceding Comment by Xu et al. (Phys. Rev. Lett. 122, 059803 (2019); arXiv:1808.05390) erroneously applies the entropic stress expression in our Letter (T.C. O'Connor et al., Phys. Rev. Lett. 121, 047801 (2018); arXiv:1806.09509) to transient stress. In addition, the authors only apply this expression at extreme extension rates where we clearly showed deviations from the entropic stress expression for steady-state extensional flow. Hence the surprisingly minor discrepancies noted in the Comment between observed and "predicted" stress are entirely expected and have no bearing on the discussion or conclusions in our Letter.