2 research outputs found
Synthesis and Self-Assembly of Perylenetetracarboxylic Diimide Derivatives with Helical Oligo(l‑lactic acid)<sub><i>n</i></sub> Segments
Three perylenetetracarboxylic diimide (PDI) derivatives
consisting
of a short oligoÂ(l-lactic acid)<sub><i>n</i></sub> (O-LLA) segment at one imide nitrogen were synthesized. The polymers
were characterized by <sup>1</sup>H NMR and gel permeation chromatography
(GPC). Their properties were investigated by differential scanning
calorimetry (DSC), X-ray diffraction (XRD) experiments, scanning electron
microscopy (SEM), electronic absorption, and circular dichroism (CD)
spectroscopy. The self-assembly behavior of these PDIs in molten state
as well as in solvent was examined. It was found that the structure
and the morphology of the self-assembly of these polymers depend on
the relative length of the O-LLA segment. The PDIs with longer O-LLA
chains present liquid crystal properties with an obvious phase transition
from disordered phase to an ordered (α) phase, which cannot
be found for the PDIs with short O-LLA segments. The long O-LLA segments
also caused a left-handed helicity for the aggregates of the PDIs
from solution. This research demonstrated that one can control the
order, aggregation mode, and morphology of the molecular aggregates
by changing the length of the O-LLA chains. This information can be
useful in the design of new organic materials that exhibit molecular
aggregation
Oil-in-Water Emulsion Templated and Crystallization-Driven Self-Assembly Formation of Poly(l‑lactide)–Polyoxyethylene–Poly(l‑lactide) Fibers
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 polyÂ(l-lactide)–polyoxyethylene–polyÂ(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