# Interfacial Viscoelastic Moduli of Surfactant- and Nanoparticle-Laden Oil/Water Interfaces Surrounded by a Weak Gel

## TL;DR

The study explores how surfactants and nanoparticles affect the elasticity of oil-water interfaces in a gel-like environment.

## Contribution

The novel contribution is understanding how different surface-active agents influence interfacial elasticity in a weak gel medium.

## Key findings

- Span 80 and nanoparticles increase interfacial elasticity in a liquid phase.
- In a weak gel, silica nanoparticles enhance elasticity while Span 80 reduces it.

## Abstract

This work aims to study the effect of the bulk rheology of a complex system on the apparent interfacial viscoelastic response of a rising oil droplet of a paraffinic oil (Indopol) undergoing sinusoidal volume dilatations insidean aqueous phase containing a hydrogel. The modulation of the interfacial viscoelasticity is obtained using Span 80 surfactant or fumed silica nanoparticles. The rheology of the continuous phase is tuned by adding 3 to 5 g/L of κ-carrageenan (KC) to switch the continuous aqueous phase from a liquid to a gel state at 15 °C. When KC is liquid, the presence of Span 80 or nanoparticles at the liquid/liquid interface increases the apparent interfacial elastic modulus. However, when KC becomes a weak gel, the apparent interfacial elastic modulus depends on the nature of the surface-active agents. Indeed, if the presence of silica hard nanoparticles enhances the apparent elasticity of the interface, adding Span 80 weakens the apparent elasticity of the interface. These trends are discussed in terms of the localization of the deformation and slippage at the interfaces.