Title: Aminopolymer Mobility and Support Interactions in Silica-PEI Composites for CO₂ Capture Applications: A Quasielastic Neutron Scattering Study

Abstract

Composite gas sorbents, formed from an active polymer phase and a porous support, are promising materials for the separation of acid gases from a variety of gas streams. Significant changes in sorption performance (capacity, rate, stability etc.) can be achieved by tuning the properties of the polymer and the nature of interactions between polymer and support. We utilize quasielastic neutron scattering (QENS) and coarse-grained molecular dynamics (MD) simulations to characterize the dynamic behavior of the most commonly reported polymer in such materials, poly(ethylenimine) (PEI), both in bulk form and when supported in a mesoporous silica framework. The polymer chain dynamics (rotational and translational diffusion) are characterized using two neutron backscattering spectrometers that have overlapping time scales, ranging from picoseconds to a few nanoseconds. Two modes of motion are detected for the PEI molecule in QENS. At low energy transfers, a “slow process” on the time scale of ~200 ps is found and attributed to jump-mediated, center-of-mass diffusion. Second, a “fast process” at ~20 ps scale is also found and is attributed to a locally confined, jump-diffusion. Characteristic data (time scale and spectral weight) of these processes are compared to those characterized by MD, and reasonable agreement is found. For themore » nanopore-confined PEI, we observe a significant reduction in the time scale of polymer motion as compared to the bulk. The impacts of silica surface functionalization and of polymer fill fraction in the silica pores (controlling the portion of polymer molecules in contact with the pore walls), are both studied in detail. Hydrophobic functionalization of the silica leads to an increase of the PEI mobility above that in native silanol-terminated silica, but the dynamics are still slower than those in bulk PEI. Sorbents with faster PEI dynamics are also found to be more efficient for CO₂ capture, possibly because sorption sites are more accessible than those in systems with slower PEI dynamics. Therefore, this work supports the existence of a link between the affinity of the support for PEI and the accessibility of active sorbent functional groups.« less

Authors:

Holewinski, Adam ^[1]; Sakwa-Novak, Miles A. ^[2]; Carrillo, Jan-Michael Y.  ^[3];

• Search DOE PAGES for author "Carrillo, Jan-Michael Y."
• Search DOE PAGES for ORCID "0000-0001-8774-697X"

Potter, Matthew E. ^[4]; Ellebracht, Nathan ^[4]; Rother, Gernot ^[5]; Sumpter, Bobby G.  ^[3];

• Search DOE PAGES for author "Sumpter, Bobby G."
• Search DOE PAGES for ORCID "0000-0001-6341-0355"

Jones, Christopher W.  ^[4]

• Search DOE PAGES for author "Jones, Christopher W."
• Search DOE PAGES for ORCID "0000-0003-3255-5791"

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+ Show Author Affiliations

1. Georgia Inst. of Technology, Atlanta, GA (United States); Univ. of Colorado, Boulder, CO (United States)
2. Georgia Inst. of Technology and Global Thermostat, LLC, Atlanta, GA (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Georgia Inst. of Technology, Atlanta, GA (United States)
5. Global Thermostat, LLC, Atlanta, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Tue May 30 00:00:00 EDT 2017

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Energy Frontier Research Centers (EFRC) (United States). Center for Understanding and Control of Acid Gas-induced Evolution of Materials for Energy (UNCAGE-ME)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)

OSTI Identifier:

1376591

Grant/Contract Number:  

AC05-00OR22725; SC0012577; DMR-1508249

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

Additional Journal Information:

Journal Volume: 121; Journal Issue: 27; Journal ID: ISSN 1520-6106

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

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