Amino-functionalized silica as a component of heat-transfer fluids

Abstract

HypothesisAmino functionalization is an efficient method of production of highly charged and finely dispersed particles of silica in water. We hypothesize that amino-functionalized silica has positive zeta potential and low degree of aggregation also in glycol and in aqueous glycol. MethodEight lots of amino-functionalized silica were prepared by different methods. The lot which showed the highest isoelectric point IEP in water was used in experiments with glycol. The particles were dispersed in glycol and in aqueous glycol and the zeta potential and particle size were measured as a function of elapsed time. On top of pH-neutral dispersions, dispersions acidified with HCl and with acetic acid were also studied. ResultsIn water and in dilute (up to 30%) glycol, amino-functionalized silica undergoes hydrolysis, which results in decrease in positive zeta potential and increase in particle size. In more concentrated glycol the particles have a stable high positive zeta potential and low particle size for at least 1 month. The positive zeta potential can be enhanced by addition of acid.