Nano-silica based Aqueous Colloidal Gels as Eco-friendly Thixotropic Lubricant

TL;DR

This paper introduces an eco-friendly, water-based silica nanoparticle gel with superior rheological and tribological properties, significantly reducing friction and wear in steel-steel contact compared to traditional lubricants.

Contribution

It presents a novel, sustainable aqueous colloidal gel with tunable rheology that achieves ultra-low friction and wear, demonstrating potential as an environmentally friendly lubricant.

Findings

Friction reduced by up to 97.46% compared to dry sliding.

Wear rate decreased by up to 99.62% under dry conditions.

The gel exhibits self-repairing and continuous film-forming capabilities.

Abstract

The environmental risks posed by traditional oil and grease-based lubricants can be significantly mitigated by adopting water-based alternatives engineered with superior rheological performance. In this work, we present a fundamentally new and environmentally sustainable aqueous thixotropic colloidal gel of silica nanoparticles formed in the presence of NaCl. We conducted a systematic and detailed investigation of their rheological and tribological characteristics. The tribological performance was evaluated against dry and water-lubricated conditions for steel-steel interface. Our experiments demonstrate that the tribological performance of the formulated nanoparticle gel can be optimized by tuning its rheological properties. A combination of super-low friction and negligible wear was observed. The friction coefficient reduced by up to 97.46% (from 0.63 to 0.016) compared to dry sliding, and by 97.04% (from 0.541 to 0.016) compared to water lubrication. Similarly, the specific wear rate decreased by up to 99.62% and 96.10% under dry conditions and water lubrication respectively. This performance is attributed to a thixotropic, chemically robust gel formed via van der Waals interactions between silica flocs, enabling self-repairing properties, continuous tribo-film formation, and a nano-bearing effect from silica nanoparticles. These attributes enable the gel to maintain and regain its structure during periods of non-shear while also forming a thin film with sufficiently low viscosity to slip into the interfacial contact zone and continuously replenish it with lubricant.