A Study for Correlation between Gas Diffusivity and Molecular Kinetic Diameter in Gas Charged Polymer Specimen

Polymer-based gas sealing technology is a key component to ensure the safety and reliability of high-pressure gas systems, and it is essential for infrastructure such as hydrogen refueling stations. In particular, the sealing performance of polymer materials used in O-rings varies depending on the gas diffusion characteristics of each gas. This necessitates a quantitative analysis of diffusion behavior for major gases including hydrogen, helium, nitrogen, oxygen, and argon. Hydrogen and helium have small molecular sizes and high diffusion rates, allowing them to easily permeate through polymer materials, while nitrogen and argon have slower diffusion rates, potentially affecting long-term sealing performance. In this study, five pure gases (H<sub>2</sub>, He, N<sub>2</sub>, O<sub>2</sub>, Ar) with different molecular kinetic diameters were used to quantitatively analyze the diffusion properties of four polymer materials (LDPE, HDPE, EPDM, NBR) under high-pressure conditions ranging from 1 to 10 MPa. A combination of a volumetric-based gas release measurement method and a pressure-based method was employed to precisely quantify the released gas volume, with compensation for ambient temperature and pressure fluctuations. From these measurements, a quantitative relationship between gas diffusivity and molecular kinetic diameter was established. The results showed that the diffusivity of gases tends to be inversely proportional to the square of the molecular kinetic diameter, consistent with predictions from the Chapman–Enskog diffusion theory. This study provides fundamental data for the design of polymer sealing materials under high-pressure gas conditions and suggests broad applicability across various gas industries, including hydrogen energy systems, semiconductor processing, fuel cells and environmental control systems.