Quantum dot-polymer interactions in contact electrification of common polymers

Abstract

Contact electrification or static charging occurs when we rub or contact insulator surfaces. This contact leads to the development of electrical charges, and accumulation of these charges may lead to uncontrolled electrostatic discharging (ESD), causing accidents, e.g., powder explosions, and economic losses in the industry. Conversely, contact charges can contribute to many application fields, such as recently developed triboelectric nanogenerators for harvesting mechanical energy. Therefore, it is crucial to control contact charges by knowing the mechanisms of contact electrification in dept. However, despite centuries of research, there are still many debates and unknowns in contact charging of polymers since it has many complex events such as electron, ion and material transfer between the surfaces. In this thesis, we studied the contact electrification of common polymers doped with quantum dots (QDs). Surface engineering of polymers at the nanoscale can open doors for new applications and give insights into contact electrification. In the first part of the thesis, we investigated the mitigation mechanisms of contact charges by doping CdSxSe1−x and CdSxSe1−x/ZnSe QDs into PDMS polymer. We tested the interaction of QDs with the polymer based on the different locations of charge carriers (electrons and holes) via a band-gap engineering approach. In the following sections of the thesis, we studied the contact charge generation in the QD-polymer composites, initially by testing the effect of ligand exchange treatment on QDs by pyridine treatment of QDs capped with oleic acid. Then, the effect of different polymer matrices was tested by doping QDs into polyethylene, polystyrene, and polymethyl methacrylate. In the last section of the thesis, nitrogen-doped carbon dots - a more biocompatible and environmentally friendly additive compared to inorganic QDs - were doped into polyvinyl alcohol to study contact charge generation. QDs and QD-doped polymers were characterized by UV-VIS spectroscopy, photoluminescence, time-resolved fluorescence, atomic force microscopy, transmission electron microscopy, and X-ray diffractometry. It was demonstrated that QDs can be used to stabilize or destabilize the contact charges on the surfaces, and this effect can be further manipulated by UV light illumination. This first-time display of the light-tunability of static charges in common polymers might help prevent excessive accumulation of charges on them or enhance the static charge stability on demand. Finally, we believe our results can be beneficial to enlighten the physical interactions of QDs with common polymers at the nanoscale and may be used to design straightforwardly-accessible materials having advanced electronic properties.