Tailor-made urethane-linked alkyl-celluloses: a promising stabilizer for oil-in-oil Pickering emulsions

Oil-in-oil emulsions or nonaqueous emulsions are formulated from two immiscible organic solvents, and provide an ideal platform for water-sensitive systems such as readily hydrolyzable reagents and polymerization in anhydrous conditions. However, surfactants to stabilize nonaqueous emulsions are scarce, severely limiting their development. Herein, we report a simple and effective strategy to transform cellulosic biomass into stabilizers for nonaqueous emulsions via decorating with alkyl chains. The process involves the activation of cellulose with N,N′-carbonyldiimidazole, followed by installing alkyl chains with different lengths via alkyl amine exchange, and the surface properties of the celluloses are finely tuned to reach a favorable state for stabilizing nonaqueous emulsions. It is demonstrated that the length of the alkyl chains significantly influences the stability and type of oil-in-oil Pickering emulsions (polar-in-nonpolar or nonpolar-in-polar), and the obtained emulsions exhibit long-term stability (even after six months). Moreover, the influences of stabilizer loadings and ratios of oil phases on the size and stability of emulsions are examined. Templated by these nonaqueous emulsions, water-sensitive thiol-isocyanate interfacial polymerizations are successfully performed to produce capsules and particles. This work proposes a simple and promising method to obtain biomass-based stabilizer for nonaqueous emulsions and thereby provides more possibilities for water-sensitive systems.