Correlated heterogeneous dynamics in glass-forming polymers

Area of Science:

• Condensed Matter Physics
• Polymer Physics
• Materials Science

Background:

• Understanding the dynamics of glass-forming materials is crucial for materials science.
• Polypropylene glycol (PPG) serves as a model system for studying glass transition phenomena.
• Tracer particle techniques provide insights into local dynamics within complex fluids.

Purpose of the Study:

• To investigate the temperature-dependent dynamics of polypropylene glycol using x-ray photon correlation spectroscopy.
• To identify different dynamical regimes and their characteristics as the glass transition temperature (Tg) is approached.
• To explore the role of dynamical heterogeneities in the intermediate temperature regime.

Main Methods:

• Utilizing x-ray photon correlation spectroscopy (XPCS) with silica tracer particles.
• Conducting experiments over a wide temperature range from room temperature down to the glass transition temperature (Tg = 205 K).
• Analyzing scattering data, including higher-order correlations, to probe particle motion and heterogeneity.

Main Results:

• Three distinct temperature regimes governing tracer particle dynamics were identified.
• At high temperatures, Brownian motion was observed.
• Near Tg, dynamics exhibited hyperdiffusive and ballistic characteristics, with significant increases in dynamical heterogeneities in an intermediate regime around 1.12Tg.

Conclusions:

• The study identifies distinct dynamical behaviors in polypropylene glycol across different temperature ranges.
• Dynamical heterogeneities significantly increase in an intermediate temperature regime, influencing particle motion.
• Correlated motion becomes prominent at temperatures near and below 1.12Tg, highlighting complex dynamics in glass formers.