Stability and thermal conductivity of TiO2/water nanofluids: A comparison of the effects of surfactants and surface modification

In this study, Surface modification technique is applied to prepare γ-glycidoxypropyltrimethoxysilane (GPTMS) modified TiO2/water nanofluids. Three surfactants and unmodified nanoparticles are added into de-ionized water to prepare surfactant added nanofluids. The characteristics of modified nanoparticles are firstly investigated. The results show that the grafting efficiency of GPTMS increases with reacting temperature and reactant mass ratio of GPTMS to nanoparticles. The stability and thermal conductivity of prepared nanofluids are investigated. The results show that the nanofluids prepared by adding Sodium dodecyl sulfate (SDS) and unmodified nanoparticles have moderate stability. The nanofluids prepared by GPTMS modified nanoparticles show excellent stability, which can be stable for 49 days and have the largest zeta potential. For all prepared nanofluids, thermal conductivity increases with temperature and nanoparticle concentration. The addition of SDS has limited contributions in thermal conductivity of nanofluids, while GPTMS modified nanofluids have higher thermal conductivity and long term thermal conductivity consistency.