Many polymers exhibit much steeper temperature dependence of their structural relaxation time (higher fragility) than liquids of small molecules, and the mechanism of this unusually high fragility in polymers remains a puzzle. To reveal additional hints for understanding the underlying mechanism, we analyzed correlation of many properties of polymers to their fragility on example of model polymer polystyrene with various molecular weights (MWs). We demonstrate that these correlations work for short chains (oligomers), but fail progressively with increase in MW. Our surprising discovery is that the steepness of the temperature dependence (fragility) of the viscosity that is determined by chain relaxation follows the correlations at all molecular weights. These results suggest that the molecular level relaxation still follows the behavior usual for small molecules even in polymers, and its fragility (chain fragility) falls in the range usual for molecular liquids. It is the segmental relaxation that has this unusually high fragility. We speculate that many polymers cannot reach an ergodic state on the time scale of segmental dynamics due to chain connectivity and rigidity. This leads to sharper decrease in accessible configurational entropy upon cooling and results in steeper temperature dependence of segmental relaxation. The proposed scenario provides a new important insight into the specifics of polymer dynamics: the role of ergodicity time and length scale. At the end, we suggest that a similar scenario can be applicable also to other molecular systems with slow intra-molecular degrees of freedom and to chemically complex systems where the time scale of chemical fluctuations can be longer than the time scale of structural relaxation.
Skip Nav Destination
Why many polymers are so fragile: A new perspective
CHORUS
Article navigation
21 October 2016
Research Article|
October 18 2016
Why many polymers are so fragile: A new perspective
C. Dalle-Ferrier;
C. Dalle-Ferrier
1
Laboratoire Léon Brillouin
, UMR 12, CEA-CNRS, 91191 Saclay, France
Search for other works by this author on:
A. Kisliuk;
A. Kisliuk
2Chemical Sciences Division,
Oak Ridge National Laboratory
, Oak Ridge, Tennessee 37831, USA
Search for other works by this author on:
L. Hong;
L. Hong
3Institute of Natural Sciences & Department of Physics and Astronomy,
Shanghai Jiao Tong University
, Shanghai 200240, China
Search for other works by this author on:
G. Carini, Jr.;
G. Carini, Jr.
4
IPCF del CNR
, UOS di Messina, I-98158 Messina, Italy
Search for other works by this author on:
G. Carini;
G. Carini
5Dipartimento di Fisica e Scienze della Terra,
Università di Messina
, I-98166 Messina, Italy
Search for other works by this author on:
G. D’Angelo;
G. D’Angelo
5Dipartimento di Fisica e Scienze della Terra,
Università di Messina
, I-98166 Messina, Italy
Search for other works by this author on:
C. Alba-Simionesco;
C. Alba-Simionesco
a)
1
Laboratoire Léon Brillouin
, UMR 12, CEA-CNRS, 91191 Saclay, France
Search for other works by this author on:
V. N. Novikov;
V. N. Novikov
6Department of Chemistry and Joint Institute for Neutron Sciences,
University of Tennessee
, Knoxville, Tennessee 37996, USA
Search for other works by this author on:
A. P. Sokolov
A. P. Sokolov
a)
2Chemical Sciences Division,
Oak Ridge National Laboratory
, Oak Ridge, Tennessee 37831, USA
6Department of Chemistry and Joint Institute for Neutron Sciences,
University of Tennessee
, Knoxville, Tennessee 37996, USA
Search for other works by this author on:
a)
Authors to whom correspondence should be addressed. Electronic addresses: [email protected] and [email protected]
J. Chem. Phys. 145, 154901 (2016)
Article history
Received:
May 15 2016
Accepted:
September 23 2016
Citation
C. Dalle-Ferrier, A. Kisliuk, L. Hong, G. Carini, G. Carini, G. D’Angelo, C. Alba-Simionesco, V. N. Novikov, A. P. Sokolov; Why many polymers are so fragile: A new perspective. J. Chem. Phys. 21 October 2016; 145 (15): 154901. https://doi.org/10.1063/1.4964362
Download citation file:
Pay-Per-View Access
$40.00
Sign In
You could not be signed in. Please check your credentials and make sure you have an active account and try again.
Citing articles via
DeePMD-kit v2: A software package for deep potential models
Jinzhe Zeng, Duo Zhang, et al.
CREST—A program for the exploration of low-energy molecular chemical space
Philipp Pracht, Stefan Grimme, et al.
Rubber wear: Experiment and theory
B. N. J. Persson, R. Xu, et al.
Related Content
Glass transition and fragility in the simple molecular glassformer CS 2 from CS 2 – S 2 Cl 2 solution studies
J. Chem. Phys. (April 2010)
An upper limit to kinetic fragility in glass-forming liquids
J. Chem. Phys. (January 2011)
Glassy properties and viscous slowing down: An analysis of the correlation between nonergodicity factor and fragility
J. Chem. Phys. (November 2008)
Kinetics of the glass transition of fragile soft colloidal suspensions
J. Chem. Phys. (December 2015)