Abstract
Nanoscale ionic materials (NIMs) are organic-inorganic hybrids prepared from ionically functionalized nanoparticles (NP) neutralized by oligomeric polymer counterions. NIMs are designed to behave as liquids under ambient conditions in the absence of solvent and have no volatile organic content, making them useful for a number of applications. We have used nuclear magnetic resonance relaxation and pulsed-field gradient NMR to probe local and collective canopy dynamics in NIMs based on 18-nm silica NPs with a covalently bound anionic corona, neutralized by amine-terminated ethylene oxide/propylene oxide block copolymers. The NMR relaxation studies show that the nanosecond-scale canopy dynamics depend on the degree of neutralization, the canopy radius of gyration, and crowding at the ionically modified NP surface. Two canopy populations are observed in the diffusion experiments, demonstrating that one fraction of the canopy is bound to the NP surface on the time scale (milliseconds) of the diffusion experiment and is surrounded by a more mobile layer of canopy that is unable to access the surface due to molecular crowding. The introduction of electrolyte ions (Na+ or Mg2+) screens the canopy-corona electrostatic interactions, resulting in a reduced bulk viscosity and faster canopy exchange. The magnitude of the screening effect depends upon ion concentration and valence, providing a simple route for tuning the macroscopic properties of NIMs. © 2013 American Chemical Society.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 9669-9675 |
| Number of pages | 7 |
| Journal | Macromolecules |
| Volume | 46 |
| Issue number | 24 |
| DOIs | |
| State | Published - Dec 2 2013 |
| Externally published | Yes |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledged KAUST grant number(s): KUS-C1-018-02
Acknowledgements: Funding provided by the Air Force Office of Scientific Research is gratefully acknowledged. The diffusion portion of this work was supported by the National Science Foundation under Grant No. DMR 04 55117. This publication is based on work supported by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST). A portion of this research was carried out while M.L.J. was a National Research Council Associate at the Air Force Research Laboratory and an employee of UES, Inc. (Dayton). Jeffamines M-2070 and M-600 were generously donated by Huntsman Corporation (Houston, TX). M. Tchoul contributed GPC in support of this study. The authors would like to thank George Fultz and Timothy Reid (University of Dayton Research Institute) for viscosity and ICP-MS data supporting this research. The authors also thankfully acknowledge Dr. Rajiv J. Berry and Phuong T. Ngo (AFRL/RX) for helpful discussions regarding this work. We would like to thank Dr. Alexander Hexemer and Dr. Eric Schaible for guidance, setup, and data collection at beamline 7.3.3 at the Advanced Light Source/ Lawrence Berkley National Laboratory. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-ACO2-05CH11231.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.