Influence of hydrophobic nanosilica and hydrophobic medium on water bound in hydrophilic components of complex systems

Abstract

The temperature behavior of water bound to compacted nanosilica cA-300 alone or in mixture with hydrophobic nanosilica AM1 alone or with addition of human serum albumin (HSA) or tannin was compared for different dispersion media (air, CDCl3 alone or with addition of HCl or trifluoroacetic acid, TFAA) using low-temperature 1H NMR spectroscopy and cryoporometry. There is overlapping of the confined space effects for water bound in voids between silica nanoparticles with the effects caused by the colligative properties of aqueous solutions of TFAA or HCl. These phenomena determine the temperature behavior of bound water unfrozen at T <273 K upon changes of the dispersion media. Typically, the contact area between unfrozen water and a surface of nanosilicas is smaller than the specific surface area of the solids due incomplete filling of voids between nanoparticles by bound water. Bound water tends to be in a clustered state upon the adsorption. In composites with cA-300/AM1, there is a tendency of diminution of the contact area of water with hydrophobic nanosilica AM1 and hydrophobic liquid CDCl3 immiscible with water. This effect changes the temperature behavior of water bound to hydrophilic silica or polar biomolecules. The observed effects can be of importance upon practical applications of nanosilica based composites.