Sorption Diffusion Coefficients Research Articles

Vapor Sorption-Desorption Phenomena of HD and GB Simulants from Polyurethane Thin Films on Aluminum Oxide via a Quartz Crystal Microbalance.

Protection and decontamination of surfaces after exposure to chemical warfare agents (CWAs) are of considerable interest to the homeland defense and battlespace operation communities. In this work, polyurethane was spin-coated onto aluminum oxide quartz crystal microbalance (QCM) sensors. Polyurethane film thickness was varied by altering the concentration of the polymer/chloroform solution used for spin-coating. Atomic force microscopy confirmed the formation of smooth, homogeneous films on the QCM sensor surface. Aluminum oxide QCM sensors coated with polyurethane were exposed to saturated vapors of dichloropentane (DCP), a mustard gas (HD) simulant, and dimethyl methylphosphonate (DMMP), a sarin gas (GB) simulant, and the mass uptake, diffusion coefficient, volume fraction, and partition coefficient of the simulant in the film were determined from QCM data. Results showed that both DCP and DMMP readily sorbed into the films although the mass uptake of DCP was greater than that of DMMP owing to DCP’s higher vapor pressure. Additionally, the CWA simulant uptake increased with polyurethane film thickness. Sorption diffusion coefficients were 1 × 10–13 cm2/s and 1 × 10–12 cm2/s for DCP and DMMP vapor, respectively. Simulant desorption was also measured and showed that some DMMP remained in the film/substrate system, while DCP sorption was fully reversible. Reversible desorption for both CWA simulants was relatively quick and independent over the range of film thicknesses studied, with average desorption diffusion coefficients of 2 × 10–9 cm2/s and 1 × 10–11 cm2/s for DCP and DMMP, respectively. Collectively, this study is expected to inform protection and decontamination strategies of equipment and structures upon exposure to CWAs.

Hydrogen sorption and desorption properties in rubbery polymer

We firstly characterized the sorption and desorption properties of hydrogen gas dissolved in rubbery polymer by utilizing a newly developed volumetric analysis technique. This method was applied to spherical-shaped sealing rubber, such as ethylene propylene diene monomer. The total sorption uptake (C∞), total desorbed content (C0), sorption diffusion coefficient (Ds) and desorption diffusion coefficient (Dd) of hydrogen in rubber are quantified as a function of diameter in both adsorption and desorption processes. No diameter dependence is observed for C∞ and C0, whereas Ds and Dd is diameter-dependent. The reversibility between C∞ and C0 observed in the process of adsorption and desorption implies the occurrence of physisorption rather than chemisorption by introducing hydrogen molecules. However, the difference between the Ds and Dd values may be ascribed to two different processes. Time to reach equilibrium in both sorption and desorption processes is found to be linearly proportional to the square of sample radius.

Well-Defined Networks from DGEBF-The Importance of Regioisomerism in Epoxy Resin Networks.

The previously ignored or unreported impact of regiosomerism within diglycidyl ether of bisphenol F (DGEBF) on its network properties is presented. Routes to the isomers of DGEBF were explored: high-performance liquid chromatography showed good separation of the three isomers [para–para-DGEBF (ppDGEBF), para–ortho-DGEBF (poDGEBF), and ortho–ortho-DGEBF (ooDGEBF)] with small yields; column chromatography gave good separation of pp- + po- from oo-DGEBF but pp-/po- separation was not achieved. Synthesis was optimized to crude yields of 76% for pp-; 87% for po-, and 86% for oo-. Subsequently, crosslinked networks were prepared with meta-xylylenediamine. With increasing ortho content, degradation of chemical resistance and an inherent weakening of the network was observed, that is, glass transition temperature (Tg), beta transition temperature (Tβ), density, crosslink density, and the desorption diffusion coefficient decreased, whereas sorption diffusion coefficient and ultimate solvent uptake increased. This clearly shows that a subtle chemical structure change can significantly impact network performance.

Sorption and Diffusion Behavior of Carbon Dioxide into Poly(l-lactic acid) Films at Elevated Pressures

Equilibrium sorption amount, desorption diffusion coefficients and sorption diffusion coefficients of CO2 in poly(l-lactic acid) (PLLA) films at elevated pressures were determined by the gravimetric method, in which the Fick's diffusion model was applied to analyze both the desorption and sorption processes. The equilibrium sorption amount of CO2 in PLLA increased with lowering temperature and elevating pressure at the temperature range from 40 to 60 °C and pressure from 104 to 2×104 kPa. Desorption diffusion coefficients were greatly influenced by the equilibrium sorption amount, and they were in the same order of magnitude as the sorption diffusion coefficients. The scan electron microscope (SEM) photos demonstrated that there was no foaming phenomenon of the PLLA film during desorption and sorption processes. The XRD spectra implied that the crystalline degree of PLLA film decreased after CO2 processing. It was concluded that PLLA polymer could be well swollen and plasticized by supercritical CO2.

Sorption, swelling, and free volume of polybenzimidazole (PBI) and PBI/zeolitic imidazolate framework (ZIF-8) nano-composite membranes for pervaporation

We have studied alcohol- and water-induced swelling and sorption of PBI and PBI/ZIF-8 nano-composite membranes and characterized both dry and wet membranes by positron annihilation lifetime spectroscopy (PALS). The degrees of membrane swelling after immersing in alcohols and water follow the order of ethanol > methanol > water > n-butanol. Addition of ZIF-8 particles into PBI membranes suppresses the ethanol-, methanol- and water-induced PBI swelling. The water-induced swelling is subdued most severely because of the hydrophobic nature and rigid structure of ZIF-8 particles, while the n-butanol-induced swelling is enhanced owing to a greater free volume in the PBI/ZIF-8 membrane. The PALS studies confirm that the high pervaporation permeability of PBI/ZIF-8 membranes is attributed to the high fractional free volume (FFV) created by large cavities of ZIF-8 particles. In addition, the alcohol saturated PBI/ZIF-8 membranes have significantly smaller free volume radii than alcohol saturated PBI membranes. A correlation among FFV, pervaporation permeability and sorption diffusion coefficient has been developed. This study also demonstrates the importance of using PALS to characterize membrane structure changes in solvent-saturated membranes at a molecular level and to correlate pervaporation performance with solvent-induced swelling.

Liquid and Supercritical Carbon Dioxide Loading into Chewing Gum Base

The sorption and loading of liquid and supercritical CO2 into chewing gum base spheres with radii of 0.5 cm was experimentally explored over the temperature and pressure ranges of 25−45 °C and 70−276 bar, respectively. Maximum loading amounts were found to be independent of temperature and to increase with increasing CO2 density. The time required to achieve maximum loading decreased with increasing temperature. A loading as high as 0.094 g of CO2 per gram of gum base was achieved. The sorption process was modeled by unsteady-state radial Fickian diffusion assuming a constant diffusion coefficient at a particular temperature and pressure (CO2 density). Volume changes of the polymer blend spheres under the conditions explored were small and ignored in the modeling. Sorption diffusion coefficients were on the order of 10-10 m2/s and increased with increasing temperature and CO2 density.

Water sorption characteristics of resin-modified glass-ionomer cements

When restorative materials take up water, their dimensions and structural integrity may be affected. This study determined, using gravimetric measurements, the water sorption characteristics of four resin-modified glass-ionomer cements (RMGICs) immersed in either distilled water or artificial saliva. The dimensional changes on water storage were also determined. The RMGICs exhibited differing characteristics as they absorbed water. Percentage water uptake and solubility of the liner/base RMGICs were significantly greater than those of the restoratives. Higher rates of water uptake, i.e. higher values of sorption diffusion coefficients, were found in the materials from one manufacturer. The desorption diffusion coefficients of the four cements were not significantly different from one another, but were significantly higher than the sorption coefficients, indicating rapid water loss from the desiccated cements. All the cements expanded on immersion in water and contracted during desorption. Greater weight increase and greater volumetric expansion were observed on long-term storage in artificial saliva than in distilled water.

Moisture Sorption Mechanism of Aromatic Polyamide Fibers: Diffusion of Moisture in Poly (p-phenylene Terephthalamide) Fibers 1

Diffusion of moisture into three kinds of Kevlar fibers—regular Kevlar, Kevlar 49, and Kevlar 149—was observed using a gravimetric method that varied vapor pressure at 25.0°C. The apparent diffusion coefficients for sorption and desorption, which were small, on the order of 10-12 cm2 / s, were found by fitting the calculated curves to the observed curves at the initial stage of the process using a Fickian model of a homogeneous cylinder. At intermediate and later stages of the sorption process, however, the observed results deviated from the calculated ones in two contrasting ways; i.e., the observed results were larger than the calculated ones for regular Kevlar and Kevlar 49 and vice versa for Kevlar 149. These results suggest a difference in the sorption mechanism, possibly due to the skin-core morphology, which is distinct for regular Kevlar and Kevlar 49 but indistinct for Kevlar 149. Referring to the skin-core mor phology with ( Dcore/ Dskin) > 1, the sorption curve was further analyzed using a coaxial cylinder model with dual components that varied (Dcore/Dskin) from 1.5 to 7 but fixed the outer and inner radius ratio ( R 2 / R1) at 1.2. The calculated results agree, in geheral, with the observed results for regular Kevlar and Kevlar 49 over the whole range of the sorption process. The Dcore values depended much more on vapor pressure than the Dskin values. In contrast, the observed results for Kevlar 149 could be accounted for if we applied the coaxial cylinder model with dual components, assuming ( Dcore/ Dskin ) < 1. The significance of the skin-core morphology as well as the interstitial and interfibrillar microvoids upon the sorption rate was discussed.

Extraction and sorption studies using linear polymer chains and model networks

AbstractModel networks have been prepared by tetrafunctionally endlinking linear polydimethylsiloxane (PDMS) chains having molecular weights Mn in the range 2000–15,000 g mole−1. The first series of networks were prepared from mixtures containing known amounts of unreactive linear PDMS chains with molecular weights Md between 1000 and 16,000 g mole−1. Rates of extraction were used to estimate diffusion coefficients; as expected, they were found to increase with increase in molecular weight Mc = Mn between crosslinks, but to decrease with increase in Md. The ease with which all of such a diluent could be removed showed the same dependence on Mc and Md. A second series of networks was prepared from the same reactive PDMS chains without diluents. Sorption and extraction studies using the same diluents were then carried out. The diffusion coefficients for sorption were found to be in the range (1.7–15.0) × 10−12 m2 s−1 and depended on both Mc and Md. The amount of diluent absorbed at equilibrium was between 10 and 70%, which is in good agreement with predictions from the Flory equation for dilation in networks, with account of constraints on crosslink fluctuations.

Study of the effect of film thickness on the sorption/desorption properties of ultra thin polymeric films

The sorption and desorption of methylene chloride in and from a styrene copolymer is described for ultra thin films in the thickness range of 1.4μ to 14.8μ. The sorption diffusion coefficient increases with decreasing film thicknesses less than about 3–4μ. This anomaly is explained in terms of a surface oxidized layer. Stress dependence and polymer relaxation effects are ruled out as explanations of this anomaly.