# Why does density increases when adding nanoparticles in a mixture of water and some clay?

I want to know that why density of drilling fluid which is a mixture of water, barrite, bentonite and carboxymethyl cellulose increases when i am adding silica nanoparticles. My ain of adding these nanoparticles is to improve the viscosity.

• The density of water is 1 ( 1 gram per cubic centimeter) but the density of silica (mineral quartz) is 2.65. Barrite has a density of 4.5, so it is much denser. – MaxW Jan 11 '16 at 20:52

Surface of silica nanoparticles have siloxane($Si-O-Si$) and silanol ($Si-OH$) groups. Because of the presence of these functional groups silica nanoparticles tend to form hydrogen bonds between themselves and/or with other polar molecules such as water. Its these interactions which reduces the intermoleculr space which further reduces the volume thus increase in density.