Phase Behavior of Medium and High Internal Phase Water-in-Oil Emulsions Stabilized Solely by Hydrophobized Bacterial Cellulose Nanofibrils

Koon-Yang Lee,Jonny J Blaker,Alexander Bismarck,Jerry Y Y Heng,Ryo Murakami

doi:10.1021/la4032514

Abstract

Water-in-oil emulsions stabilized solely by bacterial cellulose nanofibers (BCNs), which were hydrophobized by esterification with organic acids of various chain lengths (acetic acid, C2-; hexanoic acid, C6-; dodecanoic acid, C12-), were produced and characterized. When using freeze-dried C6-BCN and C12-BCN, only a maximum water volume fraction (ϕw) of 60% could be stabilized, while no emulsion was obtained for C2-BCN. However, the maximum ϕw increased to 71%, 81%, and 77% for C2-BCN, C6-BCN, and C12-BCN, respectively, 150 h after the initial emulsification, thereby creating high internal phase water-in-toluene emulsions. The observed time-dependent behavior of these emulsions is consistent with the disentanglement and dispersion of freeze-dried modified BCN bundles into individual nanofibers with time. These emulsions exhibited catastrophic phase separation when ϕw was increased, as opposed to catastrophic phase inversion observed for other Pickering emulsions.

Highlights

The pioneering work of Ramsden[1] and Pickering[2] in the early20th century showed that colloidal particles can adsorb at fluid−fluid interfaces to form stable emulsions
This is attributed to the hydrophilic nature of neat bacterial cellulose nanofibers (BCNs), which contains a large amount of hydroxyl (−OH) groups on its surface.[39]
A decrease in water uptake and an increase in toluene uptake was observed when BCN was hydrophobized by esterification with organic acids

Summary

Introduction

20th century showed that colloidal particles can adsorb at fluid−fluid interfaces to form stable emulsions. These particlestabilized emulsions are commonly known as Pickering or Ramsden emulsions (the phrase “Pickering emulsions” is more commonly used). If the three-phase contact angle is slightly higher than 90°, the particles will cause the fluid− fluid interface to bend toward the water phase, leading to the formation of w/o emulsions. Numerous authors have derived and rederived the condition for attaining the maximum stability of particle-stabilized emulsions mathematically.[5−7] This mathematical relationship relates the energy required to remove a particle from the fluid− fluid interface (ΔE) to the three-phase contact angle (θ): ΔE = πr2γ(1 ± cos θ)[2]

Methods

Results

Conclusion