Quasi-continuous melting of model polymer monolayers prompts reinterpretation of polymer melting

Abstract

Condensed matter textbooks teach us that melting cannot be continuous and indeed experience, including with polymers and other long-chain compounds, tells us that it is a strongly first-order transition. However, here we report nearly continuous melting of monolayers of ultralong n-alkane C390H782 on graphite, observed by AFM and reproduced by mean-field theory and MD simulation. On heating, the crystal-melt interface moves steadily and reversibly from chain ends inward. Remarkably, the final melting point is 80 K above that of the bulk, and equilibrium crystallinity decreases continuously from ~100% to <50% prior to final melting. We show that the similarity in melting behavior of polymers and non-polymers is coincidental. In the bulk, the intermediate melting stages of long-chain crystals are forbidden by steric overcrowding at the crystal-liquid interface. However, there is no crowding in a monolayer as chain segments can escape to the third dimension.

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Item Type:	Article
Authors/Creators:	Zhang, R. Fall, W.S. https://orcid.org/0000-0001-6778-1348 Hall, K.W. Gehring, G.A. Zeng, X. https://orcid.org/0000-0003-4896-8080 Ungar, G. https://orcid.org/0000-0002-9743-2656
Copyright, Publisher and Additional Information:	© 2021 Crown copyright. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.
Dates:	Published: 17 March 2021 Published (online): 17 March 2021 Accepted: 9 February 2021
Institution:	The University of Sheffield
Academic Units:	The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Materials Science and Engineering (Sheffield) The University of Sheffield > Faculty of Science (Sheffield) > Department of Physics and Astronomy (Sheffield)
Funding Information:	Funder Grant number Engineering and Physical Science Research Council EP/P002250/1; EP/T003294/1
Depositing User:	Symplectic Sheffield
Date Deposited:	08 Apr 2021 08:06
Last Modified:	08 Apr 2021 08:06
Status:	Published
Publisher:	Springer Nature
Refereed:	Yes
Identification Number:	10.1038/s41467-021-21799-9
Related URLs:	PubMed URL
Open Archives Initiative ID (OAI ID):	oai:eprints.whiterose.ac.uk:172801

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Quasi-continuous melting of model polymer monolayers prompts reinterpretation of polymer melting

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