TY - JOUR
T1 - Crossover from rouse to reptation dynamics in salt-free polyelectrolyte complex coacervates
AU - Yu, Boyuan
AU - Rauscher, Phillip M.
AU - Jackson, Nicholas E.
AU - Rumyantsev, Artem M.
AU - De Pablo, Juan J.
N1 - Funding Information:
We benefited from a collaboration with Heyi Liang. A.M.R. thanks Jörg Baschnagel and Albert Johner for valuable discussions. Computing resources were provided by the Laboratory Computing Resource Center (LCRC) at Argonne National Laboratory and the University of Chicago Research Computing Center (RCC). This work is supported by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The simulations reported here were carried out on the GPU cluster supported by the NSF through Grant DMR-1828629.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/9/15
Y1 - 2020/9/15
N2 - Considerable interest in the dynamics and rheology of polyelectrolyte complex coacervates has been motivated by their industrial application as viscosity modifiers. A central question is the extent to which classical Rouse and reptation models can be applied to systems where electrostatic interactions play a critical role on the thermodynamics. By relying on molecular simulations, we present a direct analysis of the crossover from Rouse to reptation dynamics in salt-free complex coacervates as a function of chain length. This crossover shifts to shorter chain lengths as electrostatic interactions become stronger, which corresponds to the formation of denser coacervates. To distinguish the roles of Coulomb interactions and density, we compare the dynamics of coacervates to those of neutral, semidilute solutions at the same density. Both systems exhibit a universal dynamical behavior in the connectivity-dominated (subdiffusion and normal diffusion) regimes, but the monomer relaxation time in coacervates is much longer and increases with increasing Bjerrum length. This is similar to the cage effect observed in glass-forming polymers, but the local dynamical slowdown is caused here by strong Coulomb attractions (ion pairing) between oppositely charged monomers. Our findings provide a microscopic framework for the quantitative understanding of coacervate dynamics and rheology.
AB - Considerable interest in the dynamics and rheology of polyelectrolyte complex coacervates has been motivated by their industrial application as viscosity modifiers. A central question is the extent to which classical Rouse and reptation models can be applied to systems where electrostatic interactions play a critical role on the thermodynamics. By relying on molecular simulations, we present a direct analysis of the crossover from Rouse to reptation dynamics in salt-free complex coacervates as a function of chain length. This crossover shifts to shorter chain lengths as electrostatic interactions become stronger, which corresponds to the formation of denser coacervates. To distinguish the roles of Coulomb interactions and density, we compare the dynamics of coacervates to those of neutral, semidilute solutions at the same density. Both systems exhibit a universal dynamical behavior in the connectivity-dominated (subdiffusion and normal diffusion) regimes, but the monomer relaxation time in coacervates is much longer and increases with increasing Bjerrum length. This is similar to the cage effect observed in glass-forming polymers, but the local dynamical slowdown is caused here by strong Coulomb attractions (ion pairing) between oppositely charged monomers. Our findings provide a microscopic framework for the quantitative understanding of coacervate dynamics and rheology.
UR - http://www.scopus.com/inward/record.url?scp=85091020695&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85091020695&partnerID=8YFLogxK
U2 - 10.1021/acsmacrolett.0c00522
DO - 10.1021/acsmacrolett.0c00522
M3 - Article
C2 - 35638633
AN - SCOPUS:85091020695
SN - 2161-1653
VL - 9
SP - 1318
EP - 1324
JO - ACS Macro Letters
JF - ACS Macro Letters
IS - 9
ER -