A nanofluid containing nanometer sized, nonagglomerated, and uniformly dispersed nanoparticles in conventional heat transfer fluids such as water or engine oils is highly desirable for successful reproduction of enhanced thermal properties. For most fine powders including nanoparticles, strong inter-attractions among the nanoparticles tend to stick the particles into agglomerates, which makes the independent dispersion of the powders difficult and, more importantly, deteriorates the final property. A proper surface modification of nanoparticles, on the other hands, could enhance their independent dispersion capability, achieve a uniform and stable dispersion, and thus fully utilize the unique properties offered by nanoparticles.

Plasma polymerization with advantages in producing ultra-thin coatings (as low as a few nanometers) provides an alternative approach in surface modification and functionalization of nanoscale materials. In this study, low-temperature plasmas of methane and oxygen mixtures were used to treat diamond nanoparticles to modify their surface characteristics and thus improve their dispersion capability in water. It was found that the plasma treatment significantly reduced water contact angle of diamond nanoparticles and thus rendered the nanoparticles with strong water affinity for dispersion enhancement in polar media such as water. Surface analysis using FTIR confirmed that polar groups were imparted on nanoparticle surfaces. As a result, improved suspension stability was observed with plasma treated nanoparticles when dispersed in water. The detailed results obtained in this study will be reported and discussed.