Local slip length and surfactant effects on liquid-infused surfaces

TL;DR

This study investigates how surfactants affect slip length on liquid-infused surfaces, revealing that surfactants significantly reduce slippage by immobilizing the liquid-liquid interface, which was confirmed through combined experimental and numerical methods.

Contribution

It provides the first experimental evidence that surfactants can immobilize liquid-liquid interfaces on textured surfaces, impacting their slip properties in flow conditions.

Findings

Surfactants reduce slip length compared to clean interfaces.

Experimental measurements align with simulations of immobilized interfaces.

Milk particles adsorb at the interface, causing slippage reduction.

Abstract

Robust surfaces capable of reducing flow drag, controlling heat and mass transfer, and resisting fouling in fluid flows are important for various applications. In this context, textured surfaces impregnated with a liquid lubricant show promise due to their ability to sustain a liquid-liquid layer that induces slippage. However, theoretical and numerical studies suggest that the slippage can be compromised by surfactants in the overlying fluid, which contaminate the liquid-liquid interface and generate Marangoni stresses. In this study, we use Doppler-optical coherence tomography, an interferometric imaging technique, combined with numerical simulations to investigate how surfactants influence the slip length of lubricant-infused surfaces with longitudinal grooves in a laminar flow. We introduce surfactants by adding tracer particles (milk) to the working fluid (water). Local measurements of slip length at the liquid-liquid interface are significantly smaller than theoretical predictions for clean interfaces (Sch\"onecker & Hardt 2013). In contrast, measurements are in good agreement with numerical simulations of fully immobilized interfaces, indicating that milk particles adsorbed at the interface are responsible for the reduction in slippage. This work provides the first experimental evidence that liquid-liquid interfaces within textured surfaces can become immobilized in the presence of surfactants and flow.