Molecular Dynamics Study of Polystyrene-b-poly(ethylene oxide) Asymmetric Diblock Copolymer Systems

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymers exhibit complex morphologies.
• Understanding molecular dynamics is crucial for predicting material properties.
• The rigid amorphous fraction (RAF) plays a significant role in polymer behavior.

Purpose of the Study:

• To elucidate the molecular dynamics of PS-b-PEO diblock copolymers.
• To investigate the molecular motion of PEO blocks within the RAF.
• To correlate copolymer nanostructure with molecular dynamics.

Main Methods:

• Dielectric spectroscopy
• Nuclear magnetic resonance (NMR) spectroscopy
• Thermal calorimetry
• X-ray scattering

Main Results:

• Identified two local Arrhenius-type processes for PEO segment motion in amorphous and RAF microphases.
• Observed two glass-transition-governed relaxations: α (amorphous phase) and αc (RAF).
• Demonstrated that αc dynamics are sensitive to nanostructure, with restricted motion in smaller PEO domains.

Conclusions:

• Local PEO segment dynamics are linked to cooperative segmental motion.
• The αc process serves as a sensitive probe of copolymer nanostructure.
• Restricted cooperative dynamics in the RAF of shorter PEO block copolymers are due to increased constraint from the PS matrix.