Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Understanding polymer dynamics near the glass transition temperature (Tg) is crucial for material properties.
• Photochromic dye tracers offer a sensitive method to probe molecular motion within polymer matrices.

Purpose of the Study:

• To investigate the diffusion behavior of a photochromic dye in polycarbonate.
• To explore the spatial scale dependence of diffusion coefficients.
• To identify potential inhomogeneities within the polymer structure.

Main Methods:

• Utilized holographic relaxation technique, specifically forced Rayleigh scattering (FRS).
• Studied diffusion at temperatures proximate to the glass transition temperature of polycarbonate.
• Varied the holographic grating period to analyze diffusion at different length scales.

Main Results:

• Apparent diffusion coefficients exhibited dependence on the spatial scale of the holographic grating.
• The observed scale dependence was successfully modeled using a two-state diffusion model.
• Evidence suggests the presence of inhomogeneities within the polycarbonate structure on the micrometer scale.

Conclusions:

• The study confirms the presence of heterogeneities in polycarbonate glasses on the micrometer scale.
• Forced Rayleigh scattering is effective in characterizing diffusion and structural inhomogeneities in polymers.
• Diffusion dynamics in polymers near Tg are complex and influenced by local structural variations.