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Solid-state microstructure of poly(l-lactide) and l-lactide/meso-lactide random copolymers by atomic force microscopy
Mantana Kanchanasopa1, Evangelos Manias, James Runt
1Department of Materials Science & Engineering and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Biomacromolecules
|September 10, 2003
Summary
Atomic force microscopy revealed poly(l-lactide) stereocopolymer lamellar morphology. Incorporating meso-lactide units reduced lamellar thickness, consistent with prior scattering experiments.
Area of Science:
- Polymer Science
- Materials Science
- Crystallography
Background:
- Poly(l-lactide) (PLLA) is a biodegradable polymer with potential applications in biomedical fields.
- Understanding the lamellar morphology of PLLA and its copolymers is crucial for tailoring material properties.
- Stereocopolymers offer tunable characteristics compared to homopolymers.
Purpose of the Study:
- To investigate the lamellar morphology of poly(l-lactide) and poly(l-lactide-co-meso-lactide) random copolymers using tapping mode atomic force microscopy (AFM).
- To analyze the effects of crystallization temperature and copolymer composition on lamellar structure.
- To compare real-space AFM findings with previous small-angle X-ray scattering (SAXS) data.
Main Methods:
- Tapping mode atomic force microscopy (AFM) was employed for real-space imaging of polymer surfaces.
- Isothermal crystallization of poly(l-lactide) and copolymers at selected temperatures.
- Qualitative and quantitative analysis of lamellar structure using AFM height and phase images.
- Examination of internal surfaces from microtomed specimens to study bulk morphology.
Main Results:
- AFM revealed distinct lamellar morphologies, with more open spherulites and screw dislocations observed at higher crystallization temperatures.
- Mean lamellar thicknesses were found to be lower in random copolymers compared to pure PLLA, especially at lower temperature differences (DeltaT).
- AFM-derived lamellar thicknesses showed good agreement with previously obtained SAXS data.
- Similar lamellar organization was observed in bulk samples (microtomed specimens) as on the surface.
Conclusions:
- Tapping mode AFM is a valuable real-space probe for studying polylactide stereocopolymer morphology.
- Meso-lactide content significantly influences lamellar thickness, with increased content leading to thinner lamellae.
- The study confirms the consistency between surface morphology observed by AFM and bulk morphology, as well as with SAXS measurements.