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    Water vapor sorption-desorption hysteresis in glassy surface films of mucins investigated by humidity scanning QCM-D

    Year: 2019

    Journal: J. Colloid Interface Sci., Volume 545, JUN 1, page 289–300

    Authors: Bjorklund, Sebastian; Kocherbitov, Vitaly

    Keywords: Relative humidity; Water vapor pressure; Glass; Glass transition; Relaxation; Polymer dynamics; Adsorption; Sorption; Desorption; Isotherms; Hysteresis

    Hypothesis: Investigating the origin of water sorption-desorption hysteresis in glassy biopolymers is important for understanding the properties of biological barriers, such as the mucus epithelium. In general, hysteresis is a result of a complex interplay between diffusion of water and relaxation of the polymer matrix. Our hypothesis is that for thin films, typical for quartz crystal microbalance with dissipation monitoring (QCM-D) experiments performed in gas phase with defined relative humidity, the diffusion limitation is eliminated and hysteresis results only from relaxation of the polymer matrix. Experiments: We use a recently developed humidity scanning (HS) QCM-D method to obtain water sorption-desorption isotherms of mucin films under controlled conditions where water diffusion is not the limiting factor, neither in the vapor phase nor in the glassy mucin film. Findings: We present new results on the water sorption-desorption behavior of glassy mucin films with nanoscale thicknesses. Despite the fact that water diffusion is not the limiting factor, the sorption-desorption branches show clear hysteresis effects that are similar to those typically observed in bulk samples. The hydration-induced glass transition, resolved from monitoring the rheological behavior of the films, is shown to be in excellent agreement with the onset of the sorption-desorption hysteresis. We suggest that the hysteresis effect is related to a difference in dynamical and structural properties of the glassy materials depending on the hydration history of the films. (C) 2019 Elsevier Inc. All rights reserved.
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