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Huang S.,Key Laboratory of Polymer Eco materials | Li H.,CAS Changchun Institute of Applied Chemistry | Wen H.,CAS Changchun Institute of Applied Chemistry | Yu D.,University of Aalborg | And 4 more authors.
CrystEngComm | Year: 2013

The crystalline morphology and structure of poly(l-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra-structures with radial periodic variation of thickness were obtained, which were induced by micro-evaporation of solvents and concentration gradient of PLLA. The ring banded morphologies consisted of multilayer lamellar crystals, which is a manifestation of alternating ridge and valley bands of periodic variation of thicknesses along the radial direction. The formation of the ring banded supra-structures is associated with diffusion and crystal growth induced periodic variation of concentration gradient, which is attributed to diffusion-related rhythmic growth and the competition between diffusion of polymer segments and growth of crystal lamellae. The mechanism of such banded-ring formation was explored on the basis of rhythmic growth resulting from non-linear diffusion. © 2014 The Royal Society of Chemistry. Source


Huang S.,Key Laboratory of Polymer Eco materials | Li H.,CAS Changchun Institute of Applied Chemistry | Shang Y.,Tianjin University | Yu D.,University of Aalborg | And 4 more authors.
RSC Advances | Year: 2013

Self-assembly of poly(l-lactide) (PLLA) in thin films induced by chloroform micro-evaporation was investigated by microscopic techniques and X-ray diffraction studies. A film-thickness dependent on highly ordered structures has been derived from disordered films. Ring-banded spherulitic and dendritic morphologies with radial periodic variation of thicknesses were formed in dilute solution driven by micro-evaporation of the solvent. Bunched morphologies stacked with a flat-on lozenge-shaped lamellae were created in thinner films. The formation of the concentric ring banded structures was attributed to the periodic rhythmic growth associated with radial periodic changes in the concentration gradient of PLLA. A diffusion-induced rhythmic growth mechanism was proposed to explain the formation of the ring banded morphologies with periodic variation of thicknesses. © 2013 The Royal Society of Chemistry. Source

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