Quartz Crystal Microbalance with Dissipation Monitoring Applications in Polymer Thin Films Analysis

Abstract

Natural and synthetic polymers are highly related to people's daily life in every perspective and determine everyone's life quality. This study investigated the interactions between polymer thin films and other molecules, specifically natural polymer films with other components in plant and fungal cell walls, crosslinked thermoplastic films with solvent molecules, as well as commodity thermoplastic films with air and moisture during aging by a powerful surface analysis instrument, a quartz crystal microbalance with dissipation monitoring (QCM-D). The assembly and interactions of glucan and chitin are crucial for understanding the fungal infection mechanism. Adsorption of mixed-linkage glucan (MLG) onto regenerated chitin (RChitin) and cellulose (RC) surfaces were investigated by QCM-D and atomic force microscopy (AFM). MLG was irreversibly adsorbed onto both surfaces and formed soft hydrogel-like layers with viscoelastic properties. This work established a QCM-D method to mimic the assembly of natural polymers in fungal cell walls and provided insight into the interactions of these polymers with chitin and cellulose. Poly(ether imide) (PEI) has poor solvent resistance towards solvents including chloroform, dimethylformamide (DMF), dichloromethane (DCM), and N-methyl pyrrolidone (NMP). Exposure to these solvents severely affects the thermal and mechanical performances of PEI. Therefore, crosslinked PEI (X-PEI) films was prepared from azide-terminated PEI (N₃-PEI-N₃) via a thermal crosslinking reaction. X-PEIs maintain outstanding solvent resistance towards common solvents by swelling ratio tests using QCM-D. Meanwhile, the thermal and mechanical properties of X-PEI were enhanced compared to the original PEI. Photo-oxidation is one of the dominant degradation mechanisms affecting the lifespan of polymers. The effect of photooxidative aging on the physiochemical properties of low-density polyethylene (LDPE) films were investigated using QCM-D, differential scanning calorimetry (DSC), and tensile stress-strain tests. The crystallinity, mechanical properties, and weight loss were correlated to understand the aging behavior. Materials after aging showed higher tensile stress and modulus, with reduced mass and elongation properties. Particularly, the aging-induced damage of polymer chain integrity was first determined by QCM-D through the evolution of mass loss during aging, providing supports to the changes of mechanical properties under aging.