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

Abstract

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:

Middleton, L. Robert ^[1]; Tarver, Jacob D. ^[2]; Cordaro, Joseph ^[3]; Tyagi, Madhusudan ^[4]; Soles, Christopher L. ^[5]; Frischknecht, Amalie L. ^[6]; Winey, Karen I. ^[1]

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+ Show Author Affiliations

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:

Thu Nov 10 00:00:00 EST 2016

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1332950

Report Number(s):

SAND-2016-11233J
Journal ID: ISSN 0024-9297; 648999

Grant/Contract Number:  

AC04-94AL85000

Resource Type:

Accepted Manuscript

Journal Name:

Macromolecules

Additional Journal Information:

Journal Name: Macromolecules; Journal ID: ISSN 0024-9297

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE