Design And Synthesis Of Novel Hydrocarbon Surfactants For Formation Of Stable C/W High Internal Volume Emulsions

Supercritical carbon dioxide?scCO₂?has been used as green solvent in many fields,however,most substance can hardly dissolve in scCO₂,which restricts its applications to some extent.Formation of CO₂/Water?C/W?high internal volume emulsions is one feasible method to avoid the weakness of scCO₂,where CO₂ can disperse into water phase as droplets.Such emulsions are highly interested in emulsion-based enhanced oil recovery and fabrication of porous materials.Only few hydrocarbon surfactants with good emulsifying ability can form the C/W emulsions.On this account,two novel hydrocarbon surfactants,i.e.,poly?vinyl acetate?-block-poly?1-vinyl-2-pyrrolidone??PVAc-b-PVP?and PVP-b-PVAc-b-PVP,were synthesized using RAFT polymerization,in which PVAc was CO₂-philic block and PVP was hydrophilic block.Their structures were precisely determined by NMR,GPC,TGA and DSC.These two copolymers can be used to form stable C/W emulsions with a high internal volume up to 90%and long stability time for more than 48 h,even up to 60 h,showing an excellent emulsifying ability.The surface tension of the surfactant aqueous solution,apparent viscosity of the C/W emulsions and solubility data were measured to systematically investigate the effect of pressure,temperature and block ratio on emulsion's stability.With the increase of pressure,the extent of surfactants dissolved by CO₂ increased,showing a better emulsifying ability.The droplets would coalesce and demulsify more easily in a higher temperature.When PVAc block was 9-21 and PVP block was 12-25,C/W interfacial tension could be reduced efficiently and they could form stable C/W emulsion in a low pressure for up to 48h.Furthermore,the emulsifying ability of surfactants with double hydrophilic tails was studied,and it turned out that surfactants with double hydrophilic tails showed stronger emulsifying ability than those with single hydrophilic tail,which could possibly provide new insight to the development of CO₂ emulsion surfactant.