Abstract
Polymer is one of the most widely used materials in almost every single field in society owing to its abundant sources, wide varieties, excellent mechanical and chemical properties, easy processability, high degree of flexibility, and so on. More recently, there are active research interest in the interaction between metal ions and polymer molecular chains. Coming from the characteristic features between the two, their synergistic interactions can bring about new mechanisms, new devices, and new applications. Due to the various changes in chemical and physiochemical characteristics of the pure polymer material after the introduction of metal ions, the polymer-metal ion complexes have been popularly studied for many possible applications, such as catalysts, water or air purification, energy conversion, sensing devices, etc. More importantly, due to the high degree of flexibility of polymers in general, flexible devices can be developed which are highly demanded for the Internet of Things (IoT) development. In this research, two research topics have been conducted by utilizing the synergistic interactions between polymer molecules and metal ions for the development of: (1) resistive switching memory device, and (2) thin film interferometer for heavy metal ion sensing.A brief summary for the two research topics is given as follows.
(1) Ion Conducting Hydrogel Based Resistive Switching Memory Device. Resistive random access memory (RRAM) has been widely studied for its potential as an alternative memristor owing to its demonstrated abilities. However, most of the reported devices are based on hard inorganic materials or stretchable organic materials which are mainly electronic conductors. By taking reference to the memory or nerve signal transmission in living organisms, one can observe the transmissions are caused by electrochemical reactions. In this part of the work, a facile approach is adopted to prepare an ion-conducting hydrogel-based RRAM device that exhibits typical write-once read-many times (WORM) resistive switching characteristics. It is worth noting that the device could be switched-on under an ultralow threshold voltage (VSET ~ 0.3 V) while the current on/off ratio exceeds 103. Moreover, the VSET could be tuned easily by changing the sweep time and voltage applied. In addition, the switched-on device could keep steady in the low resistance state for more than 3 months regardless of water evaporation from the hydrogel. Such kind of ion-conducting hydrogel-based devices could provide a new platform for possible applications involving wearable or implantable electronics, artificial organs, and biomedical devices.
(2) Thin film interferometer as a facile and high-practical method for heavy metal ion sensing.
The structural color produced by micro- or nano-structures in living organisms is a special source for the beautiful colors in nature. Of which, thin film interference generated from the interaction of light waves reflected by the film surfaces is the simplest case and has attracted much attention in exploring the stimuli-responsive structural coloration for applications. Herein, a thin film interference-based heavy metal ions sensor is reported using chitosan and its derivatives as binding materials. The pure chitosan film sensor shows higher absorption ability for Ag+ when compared with other heavy metal ions while a relatively quick responding time is needed (1min). At the same time, by taking advantage of the RGB data to build the relationship equation between them with the analyte concentration, quantitatively analyzing unknown Ag+ content is achieved. What is more, the hard Si substrate for the thin film sensor could be replaced by flexible PET/Ag, which expands the potential for applications with high demands for device flexibility. Besides, the pure chitosan film modified with functionalized carbon dots is attempted to improve the sensitivity of the thin film sensor.
By taking advantage of different polymers, metal ions as well as combination mechanisms, the polymer-metal ion complexes exhibit good application potentials in memory and sensor devices in this research study.
| Date of Award | 3 Nov 2022 |
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| Original language | English |
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| Supervisor | Kwok Yiu Robert LI (Supervisor) |