Measurement Methods for Solubility and Diffusivity of Gases and Supercritical Fluids in Polymers and Its Applications

Over the last century, polymer processes involving a gas or supercritical fluid (SCF) have attracted significant attention. The attributes of a gas/SCF in polymers benefited many polymer processing applications. In polymer applications, the solubility and diffusivity of the gas/SCF in polymers are important parameters. This review discusses experimental and theoretical methods for determining gas/SCF solubility and diffusivity in polymers. The Henry's law, Flory-Huggins, Sanchez-Lacombe, Simha-Somcynsky, and statistical association fluid theories are discussed for gas/SCF solubility in polymers. The experimental methods are categorized into five: gravimetric, piezoelectric, manometric, chromatographic, and spectroscopic methods, and are compared in terms of the operating temperatures, pressures, and types of a gas/SCF. The solubility from different methods in literatures has been compared in summary plots. In addition, the main advantages and disadvantages of each of the measurement methods are tabulated. In the diffusivity section, the steady and unsteady diffusion including the Crank's, dual-mode sorption, gas-polymer matrix, free volume, mass transfer, and empirical models are reviewed. For unsteady diffusion, the pressure decay and the gravimetric method are discussed. For steady state diffusion, the permeation method is discussed as the experimental methods. The different methods used for obtaining information on diffusivity are tabulated for comparisons.