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

## TL;DR

This study shows that using a specific ionic liquid, THEA-Ole, significantly improves the long-term stability and performance of SiO2 nanofluids.

## Contribution

THEA-Ole is shown to stabilize SiO2 nanofluids for over 60 days, surpassing conventional surfactants and typical stability limits.

## Key findings

- THEA-Ole provides minimal sedimentation and optimal dispersity in SiO2 nanofluids.
- THEA-Ole nanofluids exhibit high zeta potential and stable viscosity trends.
- PC-SAFT model confirms strong SiO2 interactions with THEA-Ole.

## 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 (\documentclass[12pt]{minimal}
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\begin{document}$$V_{m}^{E}$$\end{document}), 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, \documentclass[12pt]{minimal}
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\begin{document}$$V_{m}^{E}$$\end{document} 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.

The online version contains supplementary material available at 10.1186/s11671-026-04501-0.