Crystallization-driven surface segregation and surface structures in poly(L-lactide)-block-poly(ethylene glycol)...

Area of Science:

• Materials Science
• Polymer Science
• Surface Science

Background:

• Poly(L-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) copolymers are amphiphilic block copolymers with potential applications in various fields.
• Understanding the relationship between crystallization and surface properties is crucial for optimizing material performance.

Purpose of the Study:

• To investigate the impact of crystallization on surface segregation, crystal orientation, and morphology of PLLA-b-PEG copolymer thick films.
• To elucidate the mechanisms governing surface enrichment of polymer blocks during crystallization.

Main Methods:

• Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) for surface composition analysis.
• Reflection optical microscopy (ROM) for morphological characterization.
• Two-dimensional grazing incident wide-angle X-ray scattering (2D GIWAXS) for surface crystal orientation and crystallinity determination.

Main Results:

• Increasing PLLA crystallization temperature (T(c,PLLA)) from 70 to 110 °C significantly increased the surface fraction of the PLLA block (from 0.48 to 0.79).
• PLLA crystal lamellae exhibited preferential orientation parallel to the film surface as T(c,PLLA) increased.
• Surface crystallinity of PLLA remained largely unaffected, while PEG surface crystallinity decreased with increasing T(c,PLLA).

Conclusions:

• The observed surface enrichment of PLLA is primarily driven by a synergistic effect between crystallization behavior and surface segregation.
• Crystallization kinetics and preferred orientation of PLLA crystals play a dominant role in controlling the surface composition and structure of PLLA-b-PEG copolymers.