Concentric-ringed structures in polymer thin films.

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Traditional polymer crystallization often forms spherulites with lamellar twisting.
• Understanding novel crystalline structures is key to developing advanced polymer materials.

Purpose of the Study:

• To investigate the formation and characteristics of unique micrometer-sized banded crystalline structures in poly(bisphenol A hexane ether) (BA-C6) films.
• To elucidate the mechanism behind these novel banded structures and differentiate them from conventional polymer spherulites.

Main Methods:

• Optical Microscopy (OM) for structural observation.
• Atomic Force Microscopy (AFM) for high-resolution surface topography.
• Time-of-flight secondary ion mass spectrometry (ToF-SIMS) for chemical composition analysis.

Main Results:

• Observed novel micrometer-sized concentric banded crystalline structures in BA-C6 films.
• Identified alternating ridge and valley bands with flat-on lamellar orientation and no lamellar twisting.
• Determined that depletion zones, caused by specific volume changes and chain diffusion, drive the formation of these bands.
• Demonstrated that ridge height and interband width are controllable via diffusion rate.
• Found higher concentrations of low-molecular-weight polymer chains on ridge surfaces using ToF-SIMS.

Conclusions:

• The observed banded structures in BA-C6 films originate from a unique crystallization mechanism involving depletion zones, distinct from traditional spherulites.
• The morphology of these banded structures is influenced by polymer chain diffusion and specific volume changes.
• Control over diffusion rates offers a method to tune the structural features of these novel polymer crystals.