Experimental and atomistic simulation studies of water sorption in polyaniline

This thesis explores the possible application of doped polyaniline (PANI) fibers for recovering and producing water from atmospheric sources.; Chapter 2 details the measurements carried out for the sorption equilibrium and transport of water into commercially-produced PANI solid fibers from a 50% relative humidity air stream at ambient pressure of ∼0.1 MPa and temperature 300 K. The data were collected using a single solid fiber morphology, PANION, but with different acid dopants used to change the PANI from its emeraldine base (EB; insulating), PANI-EB, to the emeraldine salt (ES; conducting) form, PANI-ES. The sorption process was well-described by the unsteady Fickian diffusion into an infinite cylinder. The rates and equilibrium capacities depended on the acid dopant utilized, but did not vary monotonically with the anion size or the acid strength. The measured adsorption/desorption water capacities varied between 20 and 75 mg H2O/g dry polymer, depending on the anion dopant. The BF4- and H2PO 4- doped fibers had the highest capacities. When the mass loading was recalculated on a per H2O molecule/polymer repeat unit basis, most doped fibers had a capacity of ∼0.5 H2O per PANI-ES repeat unit. The exceptions were the BF4- and H2PO4- doped fibers, for which the value was ∼1. The apparent diffusion coefficients varied between 0.07-0.39 x 10-12 m2/s, and were larger during adsorption than desorption. The water capacity of the PANI solid fibers is at the upper-end of what is usually observed for glassy polymers, and provides the possibility for exploiting its electronic conductivity, good xv mechanical strength, and desiccant qualities for water recovery from atmospheric sources, as well as for advanced humidity control and sensing applications.; Chapter 3 presents the measurements performed for the sorption equilibrium and transport of water vapor into PANI asymmetric, microporous hollow fibers doped with phosphoric acid (H3PO4). The data were obtained under exposure to air streams at an ambient pressure of ∼0.1 MPa at various relative humidities and temperatures of 300--309 K. The sorption process was well-described by the unsteady Fickian diffusion into an infinite hollow cylinder. The asymmetric and porous nature of the hollow fiber's wall was represented by using an effective medium approach. The quantitative adsorption/desorption rates and equilibrium capacities depended on the experimental conditions, with the measured water capacities being between 33 and 75 mg H2O/g dry polymer under most conditions, though at the highest relative humidity (∼80% at 300 K) the fiber adsorbed almost 250 mg H2O/g. For relative humidities ≤50%, when the mass loading was recalculated on a per H2O molecule/polymer repeat unit basis, the fiber had a capacity of ∼0.5 to 1 H2O per PANI-ES repeat unit. In this same range of humidities, the apparent diffusion coefficients varied between 0.21-0.67 x 10-12 m2/s, except for the case of desorption at 80% RH wherein a value of 2.38 x 10-12 m2/s was obtained. In general, the apparent diffusion coefficients were always larger during desorption than adsorption. The water capacity of the PANI hollow fibers was found to be similar to that of the solid fiber (with the same dopant) under similar conditions.; Chapter 4 describes the atomistic simulation carried out for diffusion and sorption of water in polyaniline doped with HCl and HBr. Energy minimization and molecular dynamics simulation techniques were used to develop atomistic models of HCl- and HBr-doped conducting PANI and to study diffusion and adsorption of water vapor in these polymers. Various morphological properties of the polymers were computed, including their pair correlation functions that were found to be in good agreement with the experimental data, and their accessible free volumes. The sorption isotherms and self-diffusivity of water vapor in the polymers were also computed at various temperatures. The computed...