Non-Stationarity Effects in Polymer Membrane Swelling as Studied by Infrared Fourier Spectrometry Technique

Abstract

Nafion polymer membrane swelling mode in water poured into a cuvette, the cuvette characteristic size of the order of the membrane thickness, was investigated experimentally using the infrared Fourier spectrometry. Interest in these studies is based on the fact that, when a Nafion membrane is swelling in a cuvette sized much larger than the membrane thickness, polymer fibers are effectively unwinding into the water volume. However, this process was not studied in the case, where the area that could be occupied by the unwound polymer is limited by the cuvette size. It was shown that temporal dynamics of the polymer transition from a hydrophobic state to the hydrophilic state had several specific features depending on the cuvette size, isotopic composition, ion content and water pretreatment. It was suggested that dynamics of the cavity formation and collapse should be influenced by the dissolved gas nanobubbles. Indeed, the investigated liquid samples were not degassed. When polymer fibers are unwound, protrusions and irregularities appear on the hydrophobic membrane surface playing the role of nucleation centers for the surface nanobubbles. These nanobubbles are "carried away" by the growing fibers towards the cuvette window, and coalescence (collapse) of the nanobubbles could occur in the area of arising mechanical stresses, which should contribute to formation of a cavity. This is indirectly confirmed by results obtained in this work