Four different sized silicon-dioxide nanoparticles (5, 10, 30, and 60 nm in diameter) were dispersed in a molten salt eutectic (lithium carbonate and potassium carbonate, 62:38 by molar ratio) to obtain high temperature operating fluids (nanomaterials). A modulated differential scanning calorimeter was employed to measure the specific heat capacity of the molten salt eutectic and nanomaterials (molten salt/nanoparticle mixture). The specific heat capacity of nanomaterials was enhanced by evenly 25% over that of the base molten salt eutectic (base fluid), regardless of the size of embedded nanoparticles. The measurement uncertainty of experiments was less than 5%. Material characteristic analyses using electron microscopy show that the addition of nanoparticles into the molten salt eutectic induces nearby molten salts to form needle-like structures. These special structures were only observed within the nanomaterials whose specific heat capacity was significantly enhanced. The observed enhancements in specific heat capacity can be explained by the high specific surface energies that are associated with the high surface areas of the embedded nanoparticles and the needle-like structures induced by the nanoparticle addition. (C) 2012 Elsevier Ltd. All rights reserved.