  This study utilizes molecular dynamics simulations to scrutinize the
influence of type and volume fraction of nanoparticle on the density of
nanofluids, i.e. silver (as a hydrophilic case) and titanium dioxide (as a
hydrophobic case) water-based nanofluids. Ionic structure of TiO2 distinguishes
the solid-liquid interactions with those in silver-water nanofluid. The
thickness of nanolayer is estimated from density profile formed around the
nanoparticle and is included in the density calculation. It is found that the
type of interatomic potential between the nanoparticle and surrounding water
can highly affect the thickness of nanolayer. The hydrophobicity/hydrophilicity
of nanoparticle is of great importance in nanolayer density and its thickness.
It is observed that the difference between the traditional binary mixture and
the ternary mixture formula for calculating the density of nanofluid increases
by increasing the volume fraction of nanoparticle. This indicates that the
effect of nanolayer gets more considerable at high volume fractions.
