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Abstract. In this research, theoretical CO2 diffusivity coefficients in amorphous polymers were calculated from dielectric constant changes during CO2 desorption. These values showed agreement with experimental diffusivity coefficients from a gravimetric method. Three amorphous polymer films made from Polystyrene (PS), Polycarbonate (PC), and Cyclic Olefin Polymer (COP) resins were saturated with supercritical CO2 at 5.5 MPa and 25°C for 24 hours in a pressure chamber. The CO2 infused films were removed from the chamber for gas desorption experiments. The capacitance of the samples were recorded with an Inductance, Capacitance and Resistance (LCR) meter. These values were used to calculate the change in dielectric constants. CO2 weight percentages measured by a scale was used to calculate experimental diffusivity and solubility coefficients. It was found that the trend of dielectric constant changes was similar to that of the CO2 weight percentage changes during gas desorption. A mathematical model was built to predict the CO2 weight percentages during desorption from the measured dielectric constants. Theoretical diffusivity coefficients from this work agree well with literature data.
Keywords: polymer membranes, diffusivity, supercritical fluid (SCF), dielectric property, polymer/SCF system
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1. Introduction
Supercritical fluids (SCFs) and gases are widely used in polymer processing. For example, plastic foam products used for light-weight structural components, thermal insulation panels, and food packaging containers can be fabricated by nano-/microcellular foaming processes with gases/SCFs [1, 2]. A SCF is also used as a carrier in a polymer impregnation process, a process of depositing a solute into a polymer [3, 4]. Many properties such as rheological properties, plasticization behaviors, glass transition temperatures, and crystallization of polymers can be affected by the dissolved SCFs and gases. Gas/SCF solubility and diffusivity are two critical parameters to understand the aforementioned property changes in foaming processes. Therefore, these properties are essential to characterize in order to better understand the various processes, but they are not trivial to measure.
There are several methods to obtain gas/SCF diffusivity and solubility such as gravimetric, manometric, spectroscopic, and chromatographic methods [5-9]. However, these measurements have their limitations. For example, Magnificant Suspension Balance, based on the gravimetric methods are either expensive, complex, and/or sensitive to an electromagnetic field [6]. The instruments based on the manometric methods provide relatively simple experimental setups...