Permeability, solubility and diffusivity in polyaniline membranes and related materials.

摘要

Polyaniline has recently been shown to be an excellent material for use in the membrane-based liquid separation process known as pervaporation. Understanding the types of interactions that take place between polyaniline membranes and various liquids should make it possible to improve the properties of polyaniline membranes, including the selective separation of certain solvent pairs.; Free-standing films polyaniline that were either doped with hydrochloric acid, or that were doped and then undoped with ammonium hydroxide, were swelled in various single and binary solvents solutions. After swelling, the percentage weight gain of these films was measured. Results indicate that the concentrated and aqueous solutions of the carboxylic acids (i.e. formic, acetic and propionic) lead to significantly larger weight gains in polyaniline films than do solutions of other solvents. The compositions of the swelling solutions pulled out of polyaniline films were determined by {dollar}sp1{dollar}H-NMR. These results demonstrate that doped polyaniline films solubilize water to a greater extent than undoped polyaniline due to doped polyaniline's hydrophilicity.; Free-standing films of both doped and undoped polyaniline were also studied as pervaporation membranes for separating feed solutions of the carboxylic acids and water, and alcohols and water. The composition of all feed and permeate mixtures were determined by {dollar}sp1{dollar}H-NMR. Changing polyaniline membranes from an undoped to a fully doped state has a dramatic effect on their selectivity with regards to carboxylic acid/water and alcohol/water feeds. Fully doped polyaniline appears to restrict the permeation of liquids based on their effective sizes: large molecules such as acetic and propionic acid and 2-propanol do not permeate through doped polyaniline. The selectivities of both doped and undoped polyaniline membranes are shown to be primarily controlled by the diffusivity selectivity of these membranes. Increasing the temperature of the pervaporation experiment can lead to large increases in permeation rate. The activation energies of permeation (Ep) have also been calculated. "Permeation vs. time" experiments, where the accumulation of permeate is measured at regular time intervals over the course of a pervaporation experiment, are described. The permeabilities, time lags and diffusion coefficients of several solvents through membranes of polyaniline in both the undoped and doped form have been measured.; Derivatives and blends of polyaniline have been synthesized, characterized and used as membranes in pervaporation experiments. Pervaporation membranes of undoped derivatives of polyaniline, such as poly(o-toluidine) and poly(o-ethylaniline) show lower permeabilities, but higher selectivities than pure polyaniline. Blended membranes of polyaniline and a polymeric dopant, such as polyacrylic acid or polyamic acid, have also been used in pervaporation experiments and display membrane behavior that is intermediate between doped and undoped polyaniline. Unlike small molecule dopants such as hydrochloric acid, polymeric dopants do not leach from polyaniline membranes.