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Bound Layers "Cloak" Nanoparticles in Strongly Interacting Polymer Nanocomposites
Francis W Starr1,2, Jack F Douglas3, Dong Meng4
1Department of Physics, Wesleyan University , Middletown, Connecticut 06459, United States.
ACS Nano
|December 28, 2016
Summary
Polymer-nanoparticle interactions create a bound polymer layer that cloaks nanoparticles. This layer masks changes in the glass transition temperature (Tg) observed in experiments, clarifying nanocomposite dynamics.
Area of Science:
- Materials Science
- Polymer Science
- Computational Chemistry
Background:
- Polymer-nanoparticle (NP) interactions are crucial for nanocomposite properties.
- Experimental studies often show minimal changes in glass transition temperature (Tg) despite varying interactions.
Purpose of the Study:
- To investigate the paradoxical lack of Tg change in polymer nanocomposites with varying polymer-NP interactions.
- To elucidate the relationship between interfacial interactions, polymer dynamics, and macroscopic properties.
Main Methods:
- Molecular dynamics simulations of polymer nanocomposites.
- Systematic variation of polymer-nanoparticle interaction strengths (ε).
- Analysis of polymer dynamics and relaxation processes.
Main Results:
- A distinct, slower relaxation emerges from a "bound" polymer layer at strong polymer-NP interactions (ε > polymer-polymer interaction).
- This bound layer effectively "cloaks" nanoparticles, minimizing their impact on the bulk polymer matrix dynamics.
- Glass transition temperature (Tg), measured via thermodynamic or matrix relaxation, shows minimal dependence on ε, aligning with experimental observations.
Conclusions:
- Quasi-thermodynamic Tg measurements may not capture the altered dynamics within the bound polymer layer.
- The cloaking effect explains the experimental discrepancy between strong interfacial interactions and unchanged Tg.
- Findings are relevant for understanding polymer nanocomposite behavior and thin polymer films.
