Stability and rheological properties of nanofluids stabilized by SiO2 nanoparticles and SiO2-TiO2 nanocomposites for oilfield applications

Abstract

SiO2 nanofluids are advanced nanomaterials in which SiO2 nanoparticles (NPs) due to high specific surface area and dispersion stability may provide promising possibilities for various applications including their use for oilfield industries. However, SiO2 NPs (being solid charged particles) tend to aggregate and form NP clusters which are subjected to prematurely settle with time thus, rendering unstable and rheologically damaged nanofluid. In this work, a nanoparticle viz., TiO2 (∼50 nm) with concentration of 0.05 and 0.1 wt% was tested as co-stabilizer to improve the stability of SiO2 nanofluid [0.5 wt% SiO2 in base of polyacrylamide (PAM), called SN nanofluid] via reducing the homoaggregation and rate of sedimentation (ROS). SN nanofluid prepared using 0.5 wt% SiO2 in the presence of different concentrations of TiO2 NPs (0.05 and 0.1 wt%), called STN nanofluids, was also analyzed by dispersion stability, SEM, EDS, DLS, UV–vis, electrical conductivity, and rheological studies. Compared to SN nanofluid (dispersion stability ≈6 weeks), STN nanofluids exhibited enhanced dispersion stability of more than 10 weeks with reduced size of NP aggregates, consistent with SEM and EDS results. Electrical conductivity and UV–vis results support that SiO2 aggregates in presence of TiO2 remain suspended for longer time than sole SiO2 aggregates as witnessed by improved absorbance and electrical conductivity. Moreover, the effect of shear deformation on rheological properties (viscosity and viscoelastic moduli) of STN nanofluids was marginal than SN nanofluid, mainly due to the presence of TiO2 NP which in presence of SiO2 collectively formed nanocomposites of SiO2-TiO2 which controlled the properties of nanofluid. The study highlighted important aspects of colloidal suspensions and is a forward step towards the use of SiO2 based nanofluid for industrial applications.