%0 Journal Article
%A Ruan, Jrjeng
%A Huang, Hsing-Yuan
%A Huang, Yi-Fang
%A Lin, Chian
%A Thierry, Annette
%A Lotz, Bernard
%A Su, An-Chung
%D 2010
%T Thickening-Induced Faceting Habit Change in Solution-Grown Poly(l-lactic acid) Crystals
%U https://acs.figshare.com/articles/journal_contribution/Thickening_Induced_Faceting_Habit_Change_in_Solution_Grown_Poly_l_lactic_acid_Crystals/2786038
%R 10.1021/ma902052a.s001
%2 https://acs.figshare.com/ndownloader/files/4480417
%K PLLA
%K CrystalsMorphological evolution
%K incubation scheme
%K 10 h
%K nucleation procedure
%K lenticular crystal
%K lozenge stage
%K transmission electron microscopy
%K faceting habit
%K rhombic lozenge crystals
%K Tc
%K rhombic lozenges
%K supercooling dependence
%K α form
%X Morphological evolution of poly(l-lactic acid) (PLLA) crystals obtained via crystallization at Tc = 85 to 97 °C from 0.1% solutions in mixed xylene was closely followed via transmission electron microscopy. Upon stirring-enhanced nucleation after the adopted incubation scheme (ti = 10 h at Ti = 90 °C), there emerged “a axis” lenticular crystals of the imperfectly packed α form, as indicated by the presence of the presumably forbidden (010) spot in the selected-area electron diffraction along the [001] zone. Subsequently observed during further growth was a gradual change from lenticular to truncated lozenge with {100} and {110} facets, driven by the outward propagation of the thickened interior (truncated lozenge in shape) within the lenticular crystal. The width of the {100} facets clearly decreased with decreasing Tc, resulting in rhombic lozenges with {110} edges at 87 °C. This change in faceting habit is interpreted in terms of the competition between primary growth (controlled by surface-nucleation) and interior thickening (controlled by the reeling-in of chains from the primary thin rim via slip diffusion on the {110} surfaces). Eliminating the stirring- enhanced nucleation procedure, we have observed direct transition from lenticular to rhombic lozenge crystals at Tc = 85 °C without interior thickening, that is, bypassing entirely the truncated lozenge stage. It is hence proposed that the lamellar thickening is intrinsically a nucleation-and-growth process, initiated by the (presumably thick) nucleus from stirring, followed by the reeling-in process of stems in the rim. The supercooling dependence of the reeling-in rate is anisotropic and decreases most significantly along [100] directions with increasing Tc. Therefore, the {100} facets of truncated lozenge develop wider at higher Tc.
%I ACS Publications