Spectroscopic Investigation of Entropic Canopy-Canopy Interactions of Nanoparticle Organic Hybrid Materials

Abstract

Nanoparticle organic hybrid materials (NOHMs) are self-suspended liquid-like nanoparticle-based functional materials consisting of a surface-functionalized inorganic nanocore and oligomeric or polymeric chains. They often exhibit complex intermolecular and intramolecular interactions among their constituents, resulting in versatile physicochemical characteristics that range from glassy solids to solvent-free nanoparticle fluids. A variety of applications involving NOHMs have been investigated thus far, including thermal management fluids, lubricants, magnetic fluids, nanocomposites, electrolytes, water treatment and biomass pretreatment chemicals, and CO2 capture solvents. In particular, NOHMs have recently been recognized as a promising CO2 capture and utilization medium. To capture CO2 more effectively, a variety of specific functional groups of strong chemical affinity to CO2 can be added to the polymeric canopy (enthalpic contribution), and various steric considerations induced by attractive/repulsive interactions among the nanocores and canopies can be introduced (entropic contribution). These occur while maintaining negligible vapor pressure and enhanced thermal stability. Here, we investigated the canopy dynamics of NOHMs with different-sized SiO2 nanocores, aiming to reveal the hidden nature of the entropic interaction occurring in NOHMs. Pulse-field gradient nuclear magnetic resonance spectroscopy (with H-1) was employed to investigate the canopy dynamics of the NOHMs synthesized using 7, 12, and 22 nm SiO2 particles, and these results were compared with those from a ternary mix of all three sizes of SiO2 nanocores. The self-diffusion coefficient and thermal diffusivity were also evaluated.