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

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, C-2-; hexanoic acid, C-6-; dodecanoic acid, C-12-), were produced and characterized. When using freeze-dried C-6-BCN and C-12-BCN, only a maximum water volume fraction (phi(w)) of 60% could be stabilized, while no emulsion was obtained for C-2-BCN. However, the maximum phi(w) increased to 71%, 81%, and 77% for C-2-BCN, C-6-BCN, and C-12-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 phi(w) was increased, as opposed to catastrophic phase inversion observed for other Pickering emulsions.