Surfactant-Free High Internal Phase Emulsions Stabilized by Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are rod-like colloidal particles that irreversibly adsorb at the oil-water interface to produce ultrastable emulsions. When the internal phase fraction is increased, these CNCs can produce gel-like oil-in-water high internal phase emulsions (HIPEs) in which more than 90% of the hydrophobic phase is stabilized by less than 0.1% wt. of CNCs. However, a one-step preparation of HIPEs is not possible, and incorporation of the high internal phase fraction requires the prior preparation of Pickering emulsions. We propose that this two-step process to create CNC HIPEs relies on a swelling process of the droplets that does not desorb the CNCs from the interface, decreasing the coverage ratio of the droplets and leading to coalescence. As a result, this process leads to a drops deformation and a new interfacial networking organization as revealed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) images.