In-Situ Continuous Monitoring of the Viscosity of Surfactant-Stabilized and Nanoparticles-Stabilized Pickering Emulsions

Upinder Bains,Rajinder Pal

doi:10.3390/app9194044

Abstract

An in-situ method of measuring the viscosity of unstable and stable emulsions on a continuous basis under agitation conditions was developed and utilized to investigate the viscous behaviour of surfactant-stabilized and nanoparticles-stabilized oil-in-water (O/W) emulsions at different volume fractions of the dispersed phase (oil). The stability characteristics (droplet size and phase-separation) of emulsions under quiescent conditions were also determined with the aging of emulsions. Emulsions are Newtonian at low volume fractions of the dispersed phase. At high concentrations of the dispersed phase, emulsions behave as non-Newtonian shear-thinning fluids. The nanoparticles-stabilized (Pickering) emulsions are unstable in comparison with the surfactant-stabilized emulsions. The droplet sizes of Pickering emulsions increase rapidly with aging, whereas the droplet sizes of surfactant-stabilized remain nearly the same over a period of 24 h. However, Pickering emulsions are much more viscous than the surfactant-stabilized emulsions when comparison is made at the same volume fraction of the dispersed phase.

Highlights

Emulsions are dispersions of two immiscible liquids
The kinetic stability of emulsions can further be enhanced by reducing the rate of sedimentation or creaming of droplets by
2 shows schematic drawing and photograph the experimental were Figure prepared in a acylindrical glass vessel of capacity of approximately with The the emulsions following were prepared in adiameter cylindrical vessel=of capacity

Summary

Introduction

Emulsions are dispersions of two immiscible liquids. They are of interest in many important practical applications in the food, cosmetic, oil production, agriculture, and several other process industries [1,2,3,4,5,6]. As emulsions are created by increasing the interfacial area between the two immiscible phases, they possess a high interface free energy. There are a number of methods available to improve the thermodynamic and kinetic stabilities of emulsions. One such method is to add a surfactant to the system. The presence of a surfactant at the interface lowers the interfacial tension between the two phases and improves the thermodynamic stability. The surfactant provides a steric barrier to intimate contact between two approaching droplets and improves the kinetic stability. Surface-active polymers and amphiphilic solid nanoparticles can improve the thermodynamic and kinetic stabilities of emulsions by lowering the interfacial tension and creating a steric barrier between the approaching droplets. The kinetic stability of emulsions can further be enhanced by reducing the rate of sedimentation or creaming of droplets by

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