Investigating the effect of MnCl2 salt concentration on the droplet size and stability in a microfluidics droplets generation system

Abstract

In the realm of droplet-based microfluidic systems, achieving optimal droplet size, shape, and distribution is crucial for efficient mass transfer and reaction performance. Traditionally, surfactants have been employed to modify interfacial properties and control droplet characteristics; however, they can impact reaction environments. A novel approach gaining traction is the creation of surfactant-free droplets, where additives are minimized to preserve the liquids' inherent properties. This study aims to investigate the creation of surfactant-free emulsions using divalent ions derived from Manganese(II) chloride (MnCl2) solutions. Emulsions play a vital role in various industries, but their stability often relies on surfactants. To address this, the research examines the influence of MnCl2 concentrations (ranging from 0.2 M to 1.0 M) on droplet dynamics within an oil phase using microfluidic analysis. Notably, a distinctive non-linear correlation between ion concentration and droplet size emerges, challenging conventional assumptions. This observation highlights the intricate and nuanced interfacial interactions governing surfactant-free emulsions, showcasing potential opportunities for designing stable emulsions without traditional surfactants. For instance, droplet sizes decreased from 171 µm to 138 µm as MnCl2 concentration increased from 0.2 M to 0.4 M, demonstrating this non-linear trend. However, further increases in MnCl2 concentration to 0.8 M and 1.0 M resulted in minimal changes in droplet size.