Oil-in-Water Emulsion Templated and Crystallization-Driven
Self-Assembly Formation of Poly(l‑lactide)–Polyoxyethylene–Poly(l‑lactide) Fibers
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Abstract
A molecular
solution of an amphiphilic block copolymer may act
as an oil phase by dispersing into an aqueous micellar system of small-molecular
surfactant, forming oil-in-water (O/W) emulsion droplets. In this
paper, an as-synthesized triblock copolymer poly(l-lactide)–polyoxyethylene–poly(l-lactide) (PLLA–PEO–PLLA) was dissolved in tetrahydrofuran
(THF) and then added to an aqueous micellar solution of nonaethylene
glycol monododecyl ether (AEO-9), forming initially coalescent O/W
emulsion droplets in the size range of 35 nm–1.3 μm.
Along with gradual volatilization of THF and simultaneous concentration
of PLLA–PEO–PLLA molecules, the amphiphilic copolymer
backbones themselves experience solution-based self-assembly, forming
inverted core–corona aggregates within an oil-phase domain.
Anisotropic coalescence of adjacent O/W emulsion droplets occurs,
accompanied by further volatilization of THF. The hydrophilic block
crystallization of core-forming PEOs and the hydrophobic chain stretch
of corona-forming PLLAs together induce the intermediate formation
of rod-like architectures with an average diameter of 300–800
nm, and this leads to a large-scale deposition of the triblock copolymer
fibers with an average diameter of ∼2.0 μm. Consequently,
this strategy could be of general interest in the self-assembly formation
of amphiphilic block copolymer fibers and could also provide access
to aqueous solution crystallization of hydrophilic segments of these
copolymers