Stabilization of CO
-in-water emulsions with high internal phase volume
using PVAc-b-PVP and PVP-b-PVAc-b-PVP as emulsifying agents
Li Wen, Liwen Wang, Shuyi Fang, Lei Bao, Dongdong Hu, Yuan Zong, Ling Zhao, Tao Liu
Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology,
Shanghai 200237, People’s Republic of China
Correspondence to: T. Liu (E -mail: firstname.lastname@example.org)
Two newly-designed hydrocarbon surfactants, that is, poly(vinyl acetate)-block-poly(1-vinyl-2-pyrrolidone) (PVAc-b-PVP)
and PVP-b-PVAc-b-PVP, were synthesized using reversible addition–fragmentation chain transfer polymerization and used to form
/water (C/W) emulsions with high internal phase volume and good stability against flocculation and coalescence up to 60 h.
Their structures were precisely determined by nuclear magnetic resonance, gel permeation chromatography, thermal gravimetric anal-
ysis, and differential scanning calorimetry. Besides low temperature and high CO
pressure, the surfactant structures were the key fac-
tors affecting the formation and stability of high internal phase C/W emulsions, including the polymerization degrees of CO
block (PVAc) and hydrophilic block (PVP), as well as the number of hydrophilic tail. The surface tension of the surfactant aqueous
solution and the apparent viscosity of the C/W emulsions were also measured to characterize the surfactants efficiency and effective-
ness. The surfactants with double hydrophilic tails showed stronger emulsifying ability than those with single hydrophilic tail. The
great enhancement of the emulsions stability was due to decrease of the interface tension as well as increase of the steric hindrance in
the water lamellae, preventing a frequent collision of CO
droplets and their fast coalescence.
2018 Wiley Periodicals, Inc. J. Appl. Polym.
Sci. 2018, 135, 46351.
copolymers; foams; phase behavior
Received 29 September 2017; accepted 23 December 2017
Green solvents are increasingly needed in the chemical industry
nowadays. As the second-most abundant solvent on the earth,
carbon dioxide (CO
) has attracted much attention.
recognized as a great alternative to volatile organic solvents due
to its easy availability, cheapness, nontoxicity, nonflammability,
and moderate critical properties (T
5 31.1 8C and P
MPa). However, CO
is also known as a poor solvent having
weak van der Waals forces,
which restricts its applications in
many fields. A useful approach to solve this problem is the for-
mation and utilization of CO
/water (C/W) or water/CO
C) emulsions and microemulsions, which can be used in nano-
metal ions extraction,
enhanced oil recovery,
etc. Similar to the hydrophilic-lipophilic balance
in water-oil systems, hydrophilic-CO
(HCB) is an important characteristic of surfactant for under-
standing the morphology of the emulsions or microemulsions.
When 1/HCB is smaller than 1, the surfactant prefers the
aqueous phase and it comes out a C/W emulsion. Otherwise,
the interface will be concave with respect to water, a W/C emul-
sion will be formed.
The HCB can be manipulated by sev-
eral formulation variables including temperature, pressure,
surfactant structure, and salinity.
High internal phase C/W emulsions (also called C/W foams which
have internal phase volume >74.05%) are of great interest in CO
enhanced oil recovery.
The sweep efficiency is usually restricted
by gravity override and viscous fingering due to the low density
and viscosity of CO
After injection of a small amount of sur-
factant into the reservoir, a C/W emulsion can be formed to signif-
icantly reduce the mobility of CO
, thus increasing the sweep
Another useful application of high internal phase C/W
emulsions is synthesis of highly porous and interconnected materi-
In contrast to polymerization in O/W emulsions, this
method overcomes the disadvantage that the residual organic sol-
vent is hard to be completely removed from the materials. CO
can be removed thoroughly by depressurizing, providing an alter-
native for preparation of biomaterials in tissue engineering.
Additional Supporting Information may be found in the online version of this article.
2018 Wiley Periodicals, Inc.
J. APPL. POLYM. SCI. 2018, DOI: 10.1002/APP.46351
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