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Asymmetric Vesicle Constructed by AB/CB Diblock Copolymer Mixture and Its Behavior: A Monte Carlo Study
journal contribution
posted on 2014-08-05, 00:00 authored by Jie Cui, Yuanyuan Han, Wei JiangAsymmetric vesicles constructed from
AB/CB diblock copolymer mixture
in a selective solvent for A and C blocks are studied using Monte
Carlo simulation. The effects of the mixed ratio of the two diblock
copolymers, the solution pH, and the hydrophilic chain length on the
distributions of hydrophilic blocks on the surfaces of asymmetric
vesicles are studied systematically. The simulation results show that
asymmetric vesicle, in which the inner and outer surfaces are constructed
from different hydrophilic blocks, can be obtained from AB/CB diblock
copolymer mixture. The formation of ABC or CBA three-layer asymmetric
vesicle depends on the composition of the mixture, the chain length
of hydrophilic block, and the solution pH. The hydrophilic block with
the same charge (induced by the solution pH), or longer chain length,
or lower content in the mixture is more likely to distribute on the
outer surface of the vesicle. Moreover, the transition from ABC to
CBA three-layer asymmetric vesicle in which blocks C are charged can
occur by adjusting the composition of the mixture. On the other hand,
the investigations of the interfacial energy density of asymmetric
vesicles elucidate the distribution regularity of hydrophilic blocks.
When the hydrophilic chain lengths are equal, the difference between
the outer and inner interfacial energies is the main factor that determines
the asymmetric vesicle structures; that is, the distributions of different
hydrophilic blocks on asymmetric vesicles always tend to gain the
largest difference between the outer and inner interfacial energies.
However, when the hydrophilic chain lengths are different, the chain
conformational entropy becomes the main driving force for determining
the distribution of hydrophilic blocks on asymmetric vesicles.