skip to main content

DOE PAGESDOE PAGES

This content will become publicly available on November 10, 2017

Title: Heterogeneous chain dynamics and aggregate lifetimes in precise acid-containing polyethylenes: Experiments and simulations

Melt state dynamics for a series of strictly linear polyethylenes with precisely spaced associating functional groups were investigated. The periodic pendant acrylic acid groups form hydrogen-bonded acid aggregates within the polyethylene (PE) matrix. The dynamics of these nanoscale heterogeneous morphologies were investigated from picosecond to nanosecond timescales by both quasi-elastic neutron scattering (QENS) measurements and fully atomistic molecular dynamics (MD) simulations. Two dynamic processes were observed. The faster dynamic processes which occur at the picosecond timescales are compositionally insensitive and indicative of spatially restricted local motions. The slower dynamic processes are highly composition dependent and indicate the structural relaxation of the polymer backbone. Higher acid contents, or shorter PE spacers between pendant acid groups, slow the structural relaxation timescale and increase the stretching parameter (β) of the structural relaxation. Additionally, the dynamics of specific hydrogen atom positions along the backbone correlate structural heterogeneity imposed by the associating acid groups with a mobility gradient along the polymer backbone. At time intervals (<2 ns), the mean-squared displacements for the four methylene groups closest to the acid groups are up to 10 times smaller than those of methylene groups further from the acid groups. At longer timescales acid aggregates rearrange and the chainmore » dynamics of the slow, near-aggregate regions and the faster bridge regions converge, implying a characteristic timescale for the passage of chains between aggregates. As a result, the characterization of the nanoscale chain dynamics in these associating polymer systems both provides validation of simulation force fields and provides understanding of heterogeneous chain dynamics in associating polymers.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [1]
  1. Univ. of Pennsylvania, Philadelphia, PA (United States)
  2. National Institute of Standards and Technology, Gaithersburg, MD (United States)
  3. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  4. NIST Center for Neutron Research, Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
  5. National Institute of Standards and Technology, Gaithersburg, MD (United States); NIST Center for Neutron Research, Gaithersburg, MD (United States)
  6. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
OSTI Identifier:
1332950
Report Number(s):
SAND--2016-11233J
Journal ID: ISSN 0024-9297; 648999
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Name: Macromolecules; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Research Org:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE