Retraction of “Origin of Stress Overshoot during Startup Shear of

Retraction pubs.acs.org/macroletters

Retraction of “Origin of Stress Overshoot during Startup Shear of Entangled Polymer Melts” Yuyuan Lu, Lijia An,* Shi-Qing Wang,* and Zhen-Gang Wang* ACS Macro Letters 2014, 3 (6), 569−573, DOI: 10.1021/mz500260h

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(3) Lu, Y. Y.; An, L. J.; Wang, S.-Q.; Wang, Z.-G. Coupled Effect of Orientation, Stretching and Retraction on the Dimension of Entangled Polymer Chains during Startup Shear. Macromolecules 2014, 47, 5432−5435. (4) Lu, Y. Y.; An, L. J.; Wang, S.-Q.; Wang, Z.-G. Molecular Mechanisms for Conformational and Rheological Responses of Entangled Polymer Melts to Startup Shear. Macromolecules 2015, 48, 4164−4173. (5) Masubuchi, Y.; Watanabe, H. Origin of Stress Overshoot under Start-up Shear in Primitive Chain Network Simulation. ACS Macro Lett. 2014, 3, 1183−1186. (6) Cao, J.; Likhtman, A. E. Simulating Startup Shear of Entangled Polymer Melts. ACS Macro Lett. 2015, 4, 1376−1381.

n recent years, we published a series of four papers in ACS Macro Letters and Macromolecules1−4 reporting Brownian Dynamics simulation results on startup shear of entangled polymers for shear rates γ̇ in the regime γ̇τd > 1 but γ̇τR < 1, where τR and τd are respectively the Rouse time and reptation time. Our results showed significant chain stretching (measured by the contour length of the primitive chain) and suggested, based on analysis of the different components of stress, that the origin of the shear stress overshoot was due to chain stretching followed by retraction instead of chain orientation, in contradiction to the predictions of the reptation/tube theory. Our results also implied violation of the empirical stress-optical rule generally believed to hold in this regime, as pointed out by Masubuchi and Watanabe.5 Subsequently, Cao and Likhtman6 published their simulation results on a very similar system and found results in strong disagreement with ours  their results showed little chain stretching and conformed to the stressoptical rule. In order to resolve these discrepancies, we performed many tests, including using a new code written from scratch. We are now convinced that our previous results were wrong. Both the new code and independent runs (on LAMMPS with the “fix deform” protocol) at Akron by Yexin Zheng, a joint student between Shi-Qing Wang and Mesfin Tsige using the equilibrated copies of systems from three different sources (one of our previous copies, a copy provided by Dr. Robert Hoy, and a new copy generated at Akron), produced results similar to those reported by Cao and Likhtman. The source of errors has been identified to be in the treatment of the heat bath under shear, which resulted in much lower temperatures than T = 1 (in scaled units) for the sheared samples. The same errors were introduced in both the Langevin heat bath and the DPD heat bath. The reduced temperatures resulted in longer relaxation times. The chain stretching reported in our earlier work was thus a result of this artifact. These errors invalidate all the data at finite shear rates reported in our published papers, and render our conclusions baseless. The authors therefore request retraction of the Letter “Origin of Stress Overshoot during Startup Shear of Entangled Polymer Melts” and the other three affected articles. Publisher's Note: The Letter in question was published on May 30, 2014 and was retracted on March 15, 2017.

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REFERENCES

(1) Lu, Y. Y.; An, L. J.; Wang, S.-Q.; Wang, Z.-G. Evolution of Chain Conformation and Entanglements during Startup Shear. ACS Macro Lett. 2013, 2, 561−565. (2) Lu, Y. Y.; An, L. J.; Wang, S.-Q.; Wang, Z.-G. Origin of Stress Overshoot during Startup Shear of Entangled Polymer Melts. ACS Macro Lett. 2014, 3, 569−573. © XXXX American Chemical Society

Received: March 6, 2017

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DOI: 10.1021/acsmacrolett.7b00171 ACS Macro Lett. 2017, 6, 343−343