The confined crystallization behavior of a low molecular
weight
monodisperse polyethylene oxide (PEO) in anodic alumina oxide (AAO)
templates was investigated. Homogeneous nucleation of polymer in AAO
templates was confirmed. Within AAO with diameter larger than the
contour length of PEO chains, the “kinetics selective growth”
crystallization mechanism was confirmed based on the observation that
the chain axis preferentially aligned perpendicular to the pore axis.
However, when AAO diameter further decreases to a value smaller than
the contour length of PEO, unique orientation with chain axis aligned
parallel to the pore axis was observed for the first time. The results
were discussed based on the competition between thermodynamics and
kinetics during the crystallization process.
The
crystallization behavior of poly(l-lactic acid) (PLLA) infiltrated
in anodic alumina oxide templates (AAO) was investigated by differential
scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD).
During heating from the glassy state, the crystallization of infiltrated
PLLA was unexpectedly enhanced as compared with bulk PLLA. The cold
crystallization temperature of infiltrated PLLA from the glassy state
was much lower than that of bulk PLLA. The half-crystallization time
(t
1/2) of infiltrated PLLA at 75 °C
decreased with the diameter of AAO nanopores. The glass transition
temperature of PLLA was not influenced by the geometrical confinement.
The enhanced crystallization from the glassy state was explained by
surface-induced nucleation of AAO walls on PLLA. Our results provide
the first observation of enhanced cold crystallization of polymers
in confined geometry.
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