Visualizing and Quantifying Wettability Alteration by Silica Nanofluids

TL;DR

This study employs advanced microscopy techniques to visualize and quantify how silica nanofluids alter surface wettability, significantly reducing oil adhesion and enhancing oil recovery in porous media.

Contribution

It introduces a comprehensive visualization approach to understand wettability changes caused by silica nanofluids, revealing the formation of a porous silica layer that traps water and reduces oil adhesion.

Findings

Nanoparticles form a hierarchical porous layer on surfaces.

Water film trapping reduces oil-solid contact.

Nanofluids increase oil recovery by 8%.

Abstract

An aqueous suspension of silica nanoparticles or nanofluid can alter the wettability of surfaces, specifically by making them hydrophilic and oil-repellent under water. Wettability alteration by nanofluids have important technological applications, including for enhanced oil recovery and heat transfer processes. A common way to characterize the wettability alteration is by measuring the contact angles of an oil droplet with and without nanoparticles. While easy to perform, contact angle measurements do not fully capture the wettability changes to the surface. Here, we employed several complementary techniques, such as cryo-scanning electron microscopy, confocal fluorescence and reflection interference contrast microscopy and droplet probe atomic force Microscopy (AFM), to visualize and quantify the wettability alterations by fumed silica nanoparticles. We found that nanoparticles adsorbed onto glass surfaces to form a porous layer with hierarchical micro- and nano-structures. The porous layer is able to trap a thin water film, which reduces contact between the oil droplet and the solid substrate. As a result, even a small addition of nanoparticles (0.1 wt%) lowers the adhesion force for a 20-$\mu$m-sized oil droplet by more than 400 times from 210$\pm$10 nN to 0.5$\pm$0.3 nN as measured using droplet probe AFM. Finally, we show that silica nanofluids can improve oil recovery rates by 8% in a micromodel with glass channels that resemble a physical rock network.