Enhancement of SiO2 based nanofluid stability and thermophysical properties using surface active ionic liquids

Abstract This study addresses the challenge of achieving long-term colloidal stability in SiO2 nanofluids, a critical barrier for their practical applications, by investigating the stabilizing effects of surface-active ionic liquids (SAILs) on aqueous SiO2 nanoparticle dispersions. The purpose is to evaluate how SAILs specifically (2-hydroxyethyl)ammonium oleate (HEA-Ole), bis(2-hydroxyethyl)ammonium oleate (BHEA-Ole), and tris(2-hydroxyethyl)ammonium oleate (THEA-Ole) can enhance SiO2 stability beyond typical literature reports of less than 20 days. The stability was assessed through excess molar volume ( $$V_{m}^{E}$$ ), viscosity (η), density (ρ), DLS, zeta potential, surface tension, COSMO results, and visual observation over 60 days. The viscosity modeled by Eyring-mNRF and Eyring-NRTL, while density data were fitted with Redlich–Kister, polynomial, Ott, and PC-SAFT models. THEA-Ole demonstrated superior stabilization of SiO2, particularly after-critical micelle concentration (CMC), with minimal sedimentation, optimal dispersity via DLS, and a high zeta potential. Viscosity data aligned with Einstein, Batchelor, Brinkman, and Lundgren prediction models, $$V_{m}^{E}$$ and surface tension measurement indicated stable trends in THEA-Ole, and PC-SAFT showed the lowest ARD% for THEA-Ole nanofluids, confirming strong SiO2 interactions. THEA-Ole nanofluids provide exceptional SiO2 stability over 60 days, outperforming conventional surfactants and addressing key limitations in nanofluid dispersion for extended applications.