CO2-responsive diethylaminoethyl-modified lignin nanoparticles and their application as surfactants for CO2/N-2-switchable Pickering emulsions

Water-insoluble lignin is modified via atom transfer radical polymerization (ATRP) grafting of 2-(diethylamino) ethyl methacrylate (DEAEMA). These lignin-g-DEAEMA samples can be easily dispersed in water upon CO2 bubbling. They can also be quickly precipitated out by N-2 bubbling. The CO2/N-2-switchability of dispersion/precipitation is correlated to the graft density and chain length of DEAEMA units. This gas-switchable feature gives the lignin materials a wide range of potential applications. Demonstrated in this work is the use of lignin-g-DEAEMA as a surfactant for Pickering emulsion. An emulsion of decane is prepared with the lignin nanoparticles and it can be demulsified and re-emulsified by bubbling of the two gases. The emulsification/demulsification processes are highly reversible and easily repeatable. This work represents an innovative approach in developing value-added lignin materials.