Effect of Dispersion Stability on Electrorheology of Water-Based ZnO Nanofluids

Untreated nanoparticles possess huge surface areas compared to their mass, resulting in strong interparticle interactions in saline water. This induces a strong tendency of particles' agglomeration, rapid sedimentation, and consequently reduced mobility of nanoparticles in the aquatic environment, which ultimately lowered the effective viscosity of the nanosystem. This study aimed to investigate the effect of stabilizers on the stability of dielectric nanofluid, to provide better electrorheological characteristics for nano enhanced oil recovery (EOR) purposes. In this research, zinc oxide (ZnO) was employed as dielectric nanoparticles under various concentrations (0.1, 0.05, 0.01 wt %). Anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and oleic acid) were compared in an attempt to prepare the homogeneous dispersions with long-term stability at high temperature (similar to 95 degrees C). The laboratory experiments were designed to evaluate the sedimentation behavior of nanoparticles using visualization method; whereas UV-vis spectrophotometry was employed to quantitatively characterize the stability of the nanoparticle dispersions. Further, dynamic light scattering (DLS) was also used to determine the size distribution of dispersed nanoparticles. The stabilized nanofluids were then subjected for measuring of electrorheological behavior using a rotating viscometer attached to a custom-built solenoid coil. From the experimental results, it is concluded that the most stable aqueous dispersion of ZnO nanoparticles is obtained at 0.1 wt % with the aid of 0.025 wt % SDBS under the conditions of 60 min of ultrasonication, adjusted at the pH value of 2. The ZnO/SDBS dispersion having a hydrodynamic size of 240.9 nm exhibits extreme stability at high temperature of 95 degrees C, with the supernatant ZnO concentration decreasing only 19% compared with a decrease of 100% for the bare ZnO/Brine system. The rheological measurements indicated that all the nanofluids exhibit pseudoplastic (shear thinning) behavior. While the 0.1 wt % ZnO/SDBS dispersion provides an enhancement in the relative viscosity of nanofluid up to 11% compared to brine as a basefluid, indicating the role of stability to achieve an electrorheological effect by activating dielectric ZnO nanoparticles. Additionally, the viscosity ZnO nanofluid increased with the increase of particle concentration under an applied field, which shows the strong dependence of viscosity on particle loading. The combined treatment with the surfactant, pH, and ultrasonication is recommended to enhance the electrorheological characteristics of ZnO nanofluid. Hence, the mobility of a stabilized nanofluid can be efficiently controlled by regulating the applied field for EOR purposes.