Facile production of water-in-oil emulsions stabilized by unmodified cellulose nanocrystals using transient double emulsions technique

For hydrophilic biomacromolecules like cellulose and cellulose nanoparticles, creating water-in-oil emulsions poses significant challenges, particularly in controlling the size distribution and the interfacial composition simultaneously. Here, we introduced a simple transient double emulsion microfluidic approach for fabricating cellulose nanocrystals (CNCs) stabilized water-in-oil emulsions. It requires no chemical modifications or extra surfactants. Moreover, it allows control over the droplet size and surface coverage by simply adjusting the flow rates and particle concentration of the middle phase of the initial double emulsion. With the increase of the outer phase flow rate from 5000 μL h⁻¹ to 8000 μL h⁻¹, the diameter of the droplets significantly decreased from 236.0 ± 3.0 μm to 130.2 ± 2.2 μm. Moreover, the minimum CNC concentration required for emulsion stabilization using this method was lowered to only 0.1 wt%.This work demonstrates the feasibility of combining microfluidic techniques and double emulsion methods for producing unmodified CNCs-stabilized emulsions.