Mesophase-Mediated Crystallization of Poly(l‑lactide): Deterministic Pathways to Nanostructured Morphology
and Superstructure Control
Qiaofeng Lan
Yong Li
10.1021/acs.macromol.6b01442.s001
https://acs.figshare.com/articles/journal_contribution/Mesophase-Mediated_Crystallization_of_Poly_l_lactide_Deterministic_Pathways_to_Nanostructured_Morphology_and_Superstructure_Control/3863052
The
effect of the CO<sub>2</sub>-induced mesophase on the isothermal
crystallization of poly(l-lactide) (PLLA) was investigated
by infrared (IR) spectroscopy and microscopy. It was found that the
crystallization rate of PLLA was significantly enhanced by the CO<sub>2</sub>-induced mesophase, showing that the crystallization was completed
even in a short period of 10<sup>0</sup>–10<sup>1</sup> s.
Compared with the directly crystallized samples that showed typical
spherulites with lamellae, the crystallization via CO<sub>2</sub>-induced
mesophase led to nonspherulitic (granular or featureless) morphologies
consisting of nanorods, whereas the polymorphic behavior remained
unaffected by the initial state, resulting in crystallized PLLA containing
identical polymorphs of uniquely different nanostrutured morphologies
and superstructures. The IR imaging results indicated that the formation
of the equilibrium crystal was preceded by the formation of various
metastable intermediate phases, including mesomorphic phase, preordering,
and metastable crystal, all of which continuously evolved with time.
The nucleation process proceeded via a similar pathway. In contrast
to the negligible contribution of mesophase to the nucleation in direct
crystallization, the CO<sub>2</sub>-induced mesophase with extremely
high nucleation density underwent disordering–reorganization
into the preordering, thereby providing a tremendous number of active
nucleation sites for enhancing crystallization and serving as building
blocks for nanorods. Importantly, the present results highlight the
decisive role of mesophase in directing the nanostructure and superstructure
and support a multistep process for the crystallization (including
nucleation and crystal growth) of PLLA, validating the Ostwald step
rule, providing mechanistic insights into the crystallization of polymers.
2016-09-27 18:23:59
PLLA
Ostwald step rule
nucleation
CO 2
crystallization
IR imaging results
crystal
mesophase