Particle-particle interactions and chain dynamics of fluorocarbon and hydrocarbon functionalized ZrO2 nanoparticles

The chain conformation and dynamics of hydrocarbon and perfluorocarbon fatty acids adsorbed on 4 nm ZrO2 particles were characterized by solid-state 13C chemical shift and 19F NMR relaxation measurements, respectively, and compared to those from previous studies on lower surface area fumed metal oxide powders. The interdigitation of chains between neighboring particles, which increases with chain length, can be detected from the splitting of the 13C NMR and 19F NMR signals of the CH3 and CF3 groups, respectively. Similar to the case of alkanethiol self-assembled monolayers (SAMs) on gold nanoparticles, this interdigitation allows for efficient chain packing despite the high surface curvature. The hydrocarbon chains on the ZrO2 nanoparticles are more ordered, and the reversible chain length dependent order-disorder transition temperatures are elevated relative to those of the same fatty acids adsorbed on fumed ZrO2 powder. Likewise, the 19F spin lattice relaxation times of the fluorocarbon chains approach those of the bulk acids with increasing chain length and interdigitation, indicating densely packed chains.