Stabilization of CO2-in-water emulsions by nonfluorinated surfactants with enhanced CO2-philic tails
Several amphiphilic nonfluorinated polymers, poly(vinyl acetate)-block-poly(dimethylaminoethyl methacrylate) (PVAc -b- PDMAEMA) and poly(vinyl acetate- alt -diethyl maleate) (PVDBM) -b- PDMAEMA with different ratios of CO 2 -philic and hydrophilic groups, were synthesized using RAFT/MADIX polymerization and ATRP. Stability measurements revealed that PVDBM 8 -b- PDMAEMA 22 could emulsify 80% CO 2 in H 2 O, with stable CO 2 -in-water (C/W) emulsions observed for more than 48 h under 20.0 MPa at 25 °C, which was 20 times longer than PVAc -b- PDMAEMA did. The optimal degree of polymerization (DP) for CO 2 -philic groups in PVDBM- b -PDMAEMA was 8, because increasing the DP of PVDBM increased the CO 2 -philicity, whereas increased molecular weight limited the miscibility in water. Molecular dynamics simulations were applied to determine the hydrophilic/CO 2 -philic balance (HCB). It was found that enhanced CO 2 -philic tails widened the HCB range, and the optimal range of the HCB was varied with CO 2 -philic tail types. Both experimental and simulation results demonstrated that enhancing the CO 2 -philicty of surfactant tails can improve the stability of C/W emulsions.
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