Absorption, scattering and fluorescent properties of several different types of nanodiamond samples are measured to characterize them for various applications. Two different methods, spectrophotometry and photothermal spectroscopy were used to measure absorption properties of nanodiamonds suspended in aqueous solutions. Photothermal spectroscopy provides the advantage of measuring absorption of photoactive nanodiamonds with high-sensitivity. Spectral fluorescence properties of nanodiamond samples were studied using a commercial spectrofluorometer and a home-built inverted microscope integrated with a light-sensitive imaging spectrograph. Characteristic fluorescence spectrum of nitrogen-vacancy defects in single diamond nanocrystals was obtained using the light-sensitive instrument.

Our recent efforts using primarily nanodiamonds as lubricant additives are discussed. For traditional high performance engine oils, our results show a reduction in friction for steel surfaces for both laboratory experiments under controlled conditions and in a pilot study of passenger cars under typical driving conditions. Examination of the surfaces suggests that surface polishing at the sub-micron scale may be responsible for these results. A separate set of experiments using a quartz crystal microbalance to measure dissipation and drag due to friction has shown that when added to water the charge of the nanodiamond acquired from surface functionalization can have a large influence on uptake and friction at the water-metal interface. More importantly, these results suggest the possibility of creating nanodiamonds with controllable frictional drag at the solid-liquid interface through surface processing. Companion simulation results for nanodiamonds in water sliding between diamond surfaces are also presented. Future possibilities for further understanding and tuning the properties of nanodiamonds as lubricant additives through synergistic experiments and modeling are also discussed.