The evolution of acidic and ionic aggregates in ionomers during microsecond simulations.
Amalie L Frischknecht1, Karen I Winey2
1Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
The Journal of Chemical Physics
|February 17, 2019
Summary
Molecular dynamics simulations reveal that lithium-neutralized poly(ethylene-co-acrylic acid) ionomers form ionic aggregates. Higher temperatures promote aggregate mobility and steady-state formation, influencing material properties.
Area of Science:
- Materials Science
- Polymer Chemistry
- Computational Chemistry
Background:
- Poly(ethylene-co-acrylic acid) ionomers are advanced materials with tunable properties.
- Understanding ionic aggregate formation is crucial for optimizing ionomer performance.
Purpose of the Study:
- To investigate the influence of temperature and spacer length on ionic aggregate morphology in lithium-neutralized ionomers.
- To elucidate the dynamics of aggregate formation and steady-state attainment.
Main Methods:
- Atomistic molecular dynamics simulations were conducted for microsecond durations.
- Simulations were performed on poly(ethylene-co-acrylic acid) ionomers with varying spacer lengths and neutralization levels.
- Two temperatures (423 K and 600 K) were explored.
Main Results:
- Ionic aggregates of various shapes, from isolated to percolated, were observed.
- At 423 K, aggregate morphologies did not reach a steady state within the simulation time.
- At 600 K, aggregates became mobile, reaching steady state after hundreds of nanoseconds.
- 100% neutralized systems exhibited percolated aggregates spanning the simulation box.
- Partially neutralized systems showed coexisting lithium ion and hydrogen-bonded acid group aggregates.
Conclusions:
- Temperature significantly impacts ionic aggregate dynamics and morphology.
- Aggregate structure is dependent on neutralization degree and spacer length.
- Unneutralized acid groups in lithium ion aggregates tend to localize at the aggregate periphery.
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