(615a) Effect of Nonfluorinated Surfactants on the Interfacial Stabilization of CO2-in-Water (C/W) Emulsion: A Molecular Dynamics Simulation

Effect of nonfluorinated surfactants on the interfacial stabilization of

 CO₂-in-water (C/W) emulsion

Dong-dong Hu, Lei Bao, Li Wen, Liwen Wang, Ling Zhao, Tao Liu*

 (Shanghai Key Laboratory of Multiphase
Materials Chemical Engineering, East China University of Science and
Technology, Shanghai 200237, China)

hudd@ecust.edu.cn,
liutao@@ecust.edu.cn; Phone: +86-21-64253470

Supercritical
carbon dioxide (scCO₂) is of interest as a potential alternative to conventional organic solvents. Unfortunately, its low polarizability per volume and low dielectric constant
leading usual surfactants cannot stabilize CO₂ in water. Some efficient but toxic and expensive fluorinated surfactants were
found to form CO₂-in-water (C/W) emulsion or foams. Our preview works
investigated that the enhanced CO₂-philic tails can
improve the stability of C/W emulsions by studying poly(vinyl acetate-alt-diethyl
maleate)-b-poly(dimethylaminoethyl methacrylate)
(PVDBM-b-PDMAEMA) and poly(vinyl
acetate)-b-PDMAEMA(PVAc-b-PDMAEMA).

In this
work, the effect of nonfluorinated surfactants on the
stabilization of C/W emulsion was investigated. And the interfacial properties
were studied by using a molecular dynamics simulation. Polyethylene glycol
(PEG) and poly(1-vinyl-2-pyrrolidone) (PNVP) were chosen as hydrophilic tails
while PVDBM and PVAc were chosen as CO₂-philic tails. PVDBM-b-PEG and PVAc-b-PNVP
were designed as the nonfluorinated surfactants. From the experiment, PVDBM₅-b-PEG₃₂
could emulsify 90% CO₂ in H₂O at 25 ¡ãC under 20.0 MPa for
more than 24 hours. PVAc₉-b-PNVP₁₂ is able to form a stable emulsion when the pressure is elevated to
11.5 MPa. An obvious trend shows that the
stability of emulsions enhance with increasing CO₂ pressure. At a
constant temperature, with increasing CO₂ pressure, the cohesive
energy density of CO₂ would increase, as well as the solvation power
of CO₂. The MD simulation studies in this work aim to gain a more
precise molecular-level picture about how the surfactant affects the interfacial
properties, transport process of CO₂, and then the interfacial
stabilization of C/W emulsion.

Fig. 1
Photographs of stable C/W emulsion (Left)
and emulsion breaking (Right)

Fig. 2 Density distributions
for the systems of CO₂/H₂O with surfactants at 35 ^oC, 20 MPa.

(a) 0.2 %
PVDBM-PEG; (b) 0.5 % PVDBM-PEG; (c) 0.2 % PVAc-PNVP; (d) 0.5 % PVAc-PNVP

Acknowledgement:

The authors are grateful to the National Science Foundation of China (21676081, 21706063) and The Fundamental Research Funds for the Central Universities
(22221714005)

References:

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