(179g) Stabilization of Silica Nanofluids At Neutral pH and Evaluate the Effect of Coating Concentration

The presence of nano-sized particles in thermal fluid is known to enhance the thermal properties of the suspension, such as thermal conductivity and thermal diffusivity, relative to the base fluid. Significant enhancements have been reported even at low volume fractions of nanoparticles. This enhancement is important becasue it would lead to decrease the size and capital costs of heat transfer equipement and more efficient use of energy. Commercial nanofluids are now available in the market but a practical problem that limits their utilitiy is poor colloidal stability, which results in aggregation, increased viscosity precipitation, and loss of thermal enhacement. Our approach is to attach covaelently  a self-assembled monolayer (SAM) of suitable chains onto the particle surface to (a) passivate the surface of the particles and (b) to improve stability via ionization of surface groups on the SAMs themeselves. We have tested and show results for the following aminosilanes:  3-aminopropyltriethoxysilane (APES), aminopropyldimethylethoxysilane (APMS), and  N-[3-(trimethoxysilyl)propyl]ethylenediamine (TMPE) were used to modify the surface of silica colloidal nanoparticles. We provide colloidal characterization for each SAM, report optimum coating conditions,  and evaluate the effect of each SAM concentration on the stability of the nanofluid  at different pH values. Since TMPE shows to be the best candidate for the coating process, thermal stability test was also done for it.