Volume Dependence of Hydrogen Diffusion for Sorption and Desorption Processes in Cylindrical-Shaped Polymers

Area of Science:

• Materials Science
• Chemical Engineering
• Polymer Science

Background:

• Gas transport properties under high pressure are crucial for applications.
• Sample size dependence and permeation efficiency are key factors in gas sorption.
• Understanding hydrogen sorption and desorption in polymers is vital for material development.

Purpose of the Study:

• To measure hydrogen sorption and desorption properties in polymers.
• To investigate the influence of sample size (thickness and diameter) on diffusion and equilibrium times.
• To determine the relationship between polymer dimensions and hydrogen transport characteristics.

Main Methods:

• Utilized a modified volumetric analysis technique to measure hydrogen sorption and desorption.
• Determined parameters including total uptake (C∞), total desorbed content (C0), diffusion coefficients (Ds and Dd), and equilibrium times (ts and td).
• Analyzed the impact of polymer thickness and diameter on these measured parameters.

Main Results:

• Total hydrogen uptake (C∞) and desorbed content (C0) showed no significant volume dependence, indicating reversible physisorption.
• Hydrogen diffusivity increased with polymer thickness above 5 mm.
• Desorption diffusion coefficients (Dd) were larger than sorption diffusion coefficients (Ds), possibly due to polymer swelling and chain scission.
• Sorption (ts) and desorption (td) equilibrium times were linearly proportional to the square of thickness for aspect ratios above 3.7.

Conclusions:

• Polymer thickness significantly influences hydrogen diffusion coefficients and equilibrium times.
• The observed linear relationship between equilibrium times and thickness squared allows for predictive modeling.
• Findings provide insights into hydrogen storage and transport mechanisms in polymers, aiding in material design for high-pressure applications.