Heat Transfer Fluids Based on Amino-Functionalized Silica Dispersed in 1,2-Propylene Glycol and in 50-50 Aqueous 1,2-Propylene Glycol

1,2-propylene glycol and its 50-50 w/w mixture with water were used to prepare heat transfer fluids based on amino-functionalized silica. On top of pH-neutral dispersions (no reagents added except for the solvent and the particles), dispersions acidified with acetic acid and with HCl were used to enhance the positive electric charge of silica particles. The colloidal particles had a positive zeta potential >40 mV and showed apparent particle radii of 70 nm, and these properties remained unchanged on heating up to 80 degrees C for up to 28 days.