Anomalous diffusion of chains in semicrystalline ethylene polymers

Area of Science:

• Polymer Science
• Materials Science
• Solid-State Physics

Background:

• Semicrystalline polymers, like ethylene homo- and copolymers, possess both crystalline and amorphous/interfacial regions.
• Understanding chain dynamics within these distinct regions is crucial for predicting material properties and performance.
• Previous studies have explored chain mobility, but the specific diffusion mechanisms in crystalline regions remain a topic of interest.

Purpose of the Study:

• To investigate the chain diffusion dynamics between crystalline and amorphous/interfacial regions in semicrystalline ethylene polymers.
• To characterize the nature of chain segment diffusion within the crystalline regions.
• To determine if standard diffusion models apply to crystalline chain segment movement.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy was employed to probe molecular motion.
• The study focused on ethylene homo- and copolymers exhibiting semicrystalline structures.
• Analysis involved measuring the mean-square displacement of chain segments over time.

Main Results:

• Chain diffusion between crystalline and amorphous/interfacial regions was successfully investigated.
• A key finding is that crystalline chain segment diffusion along the chain-folded path is anomalous.
• This anomalous diffusion is quantitatively described by the scaling relation: mean-square displacement approximately t(1/2).

Conclusions:

• The diffusion of crystalline chain segments in semicrystalline ethylene polymers deviates from normal diffusion behavior.
• The observed anomalous diffusion, characterized by ~ t(1/2), provides a new understanding of chain dynamics in the crystalline phase.
• These findings have implications for the design and processing of semicrystalline polymers, influencing their mechanical and thermal properties.