A blob model to parameterize polymer hole free volumes and solute diffusion

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Solute diffusion in solid polymers is crucial for applications but poorly understood.
• Diffusion behavior differs significantly between molten and solid polymer states.
• Existing models lack broad applicability across diverse polymer types.

Purpose of the Study:

• To develop a new model for predicting solute diffusion in solid polymers.
• To quantify hole-free volume in various polymers using scale-invariant diffusivities.
• To extend the applicability of the free-volume theory (FVT) to a wider range of polymers.

Main Methods:

• Utilized the scale invariance of linear probe diffusivities (D) based on blob (M_blob) and anchor (M_anchor) masses.
• Evaluated hole-free volumes in seven different polymers across a wide temperature range (T-Tg).
• Applied a new parameterization of free-volume concepts to enable FVT application.

Main Results:

• Successfully estimated hole-free volumes in diverse polymers.
• Analyzed and quantified enthalpic and entropic effects of solute structures (blobs and anchors).
• Achieved accurate blind validation by predicting diffusivities of water and toluene in polyethylene terephthalate and other polymers.

Conclusions:

• The new blob model and reformulated FVT offer a universal approach to understanding solute diffusion in solid polymers.
• This framework facilitates the rational design of polymer additives with tailored diffusion properties.
• Opens new avenues for optimizing materials in packaging, reservoir, and biomedical technologies.