Thu, 16 May, 2024
Research undertaken as part of the Non-metallic Innovation Centre (NIC) has been published in the latest issue of the peer reviewed Journal of Polymer Testing, published by Elsevier.
The paper, written by Hamad Raheem as part of his PhD project, was co-authored with TWI Technology Fellow Dr Bernadette Craster and Professor Ashwin Seshia University of Cambridge. ‘A comparison of calculation methods for the diffusion coefficient as a potential tool for identifying material alteration with time’ can be read in full, here.
Figure 1. Normalised ratio of diffused substance plotted against the square root of experimental time
The paper addresses the calculation of diffusion coefficients of CO2 gas through PE-RT from continuous sweep permeation tests after different run times.
Knowing the permeability and diffusion coefficients allows the solubility and concentration in the polymer film to be calculated. Other permeation methods used more often in engineering applications, such as the closed cell manometric method, traditionally provide estimates of the lag time diffusion coefficient often after just hours of first exposure.
This study investigates methods such as those fitting the transients like the Taylor expansion, inflection of the first derivative of the flux, and variations in the calculations of the diffusion coefficient using chosen times in the flux curve (e.g., time-lag, half-point flux, Yen Shih method and similar fits). These methods can be implemented at various stages in the development of the permeation trace over several weeks.
The time-lag method was compared to the other published methods to verify its effectiveness as a convenient technique for engineers to accurately estimate single gas diffusion in polymer films. It was found that the time-lag method ranged in agreement with the other published methods from less than 1% to up to 27%.
The approaches presented in the paper support the study of transport coefficients employed for detecting alterations in polymeric structures.