Macromolecular hydration phenomena An overview of DSC studies on sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion) and cellulose biopolymer materials

摘要

Water plays an important role in the physicochemical and mechanical properties of Nafion (poly tetrafluorosulfonic acid) and cellulosic materials. Due to the strong influence of hydration on the properties of these materials, the mechanism and molecular-level understanding of hydration processes are the subject of ongoing interest in food, environmental and energy science. Nafion is a sulfonated tetrafluoroethylene polymer that represents a prototypical polymer electrolyte membrane (PEM) material. PEMs are often composed of a hydrophobic backbone with a strongly hydrophilic region (e.g., sulfonic acid moieties), which are directly attached to the backbone or through a pendant group. The application of Nafion in fuel cells as PEMs necessitate that the hydration properties of the membrane play an important role for maintaining high proton conductivity and mechanical properties. Cellulose on the other hand is one of the most abundant and low-cost renewable biopolymers with unique hydration properties. The hydration of cellulose impacts its biodegradability, recyclability and tunable physicochemical properties for various applications employing composite materials, pharmaceutical delivery systems, paper production, fibers and biofuel production. One of the challenges in the development and valorization of cellulose-based materials relates to its insolubility in aqueous media and conventional solvents. Therefore, evaluation of the hydration properties of Nafion and cellulose materials is required in order to characterize their physicochemical properties. Studies of the hydration properties of these materials include dielectric, spectroscopic techniques (NMR and IR), dynamic vapor sorption, differential scanning calorimetry (DSC), viscometry and computer simulations to determine the structural, kinetic and thermodynamic properties associated with such hydration processes. DSC is a sensitive and versatile thermal analysis method for the study of hydration phenomena, thermal behavior and thermodynamic state of water in hydrated macromolecular systems. The aim of this minireview is to provide an overview of recent DSC studies relevant to aspects of hydration phenomena for Nafion and cellulose. This overview will contribute to an improved understanding of the hydration properties of Nafion and cellulose materials for applications that involve hydration phenomena.