Engineering

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  • (2021) Chua, Stephanie
    Thesis
    Improvements in liquid lithium-ion battery electrolytes using of metal organic frameworks (MOFs) as a functional decoration on polymer membrane separators were investigated using a combination of experimental and theoretical methods. Zirconium-based MOF UiO-66 was introduced to the polymer support using the mixed matrix membrane (MMM) method. The method allowed the one-step manufacture of a robust, mechanically pliable polymer-MOF membrane composite of high MOF loading. MOF-MMMs imparted improved electrochemical behaviours such as a widened potential operating window, near-unity transference number, and increased presence of solid electrolyte interphase (SEI) components crucial to battery performance. Density functional theory (DFT) calculations were also performed to provide insights regarding electrolyte solvation in the presence of MOF. A simple dip-coating technique was utilised to modify the surface of the MOF-MMMs with polydopamine (PDA) for further improvement of the electrochemical properties. Increased transference numbers, as well as stability during rate cycling, were observed with the resulting PDA-MMM owing to the improved electrode/electrolyte interface. However, surface analyses using x-ray photoelectron spectroscopy (XPS) showed that there are reduced amounts vital SEI components compared to the original MOF-MMM support. The last section further explores the versatility of UiO-66 and tackled the preparation of gel polymer electrolytes (GPEs) decorated with UiO-66 via phase inversion technique. Using the phase inversion method, the fabricated GPE contained pores from both polymer substrate and the intrinsic pores of the 3D nanomaterial for improvement of electrochemical properties. It was demonstrated in this work that the MOF GPE is equally inert and suitable in ether or carbonate-based electrolytes. Overall, this study demonstrated the versatility of UiO-66 metal organic frameworks for use as a functional nanofiller for electrolyte membranes. With the use of inexpensive membrane fabrication methods, the composites obtained are viable for lithium-metal battery applications. Similarly, insights drawn can provide a springboard towards future study of MOF-based electrolytes.

  • (2022) Qiao, Laicong
    Thesis
    There has been a rapid-growing market and academic enthusiasm for small wearable molecular diagnostic platforms driven by the growing demand for continuous monitoring of human health. Wearable devices need to be portable, stretchable, and ideally re-configurable to be able to work for different analytes. Such flexible physiological monitoring devices which are non-invasive or minimally-invasive represent the next frontier of biomedical diagnostics. They may make it possible to predict and prevent diseases or facilitate treatment by diagnosing diseases at the initial stages. However, there are many problems that restrict further applications of these devices. Firstly, there are a limited number of bio-materials which are highly flexible, biocompatible and have anti-fouling properties; such biomaterials are needed as substrates for wearable devices. Secondly, traditional biosensors used in wearable devices focus on the detection of physical signals (such as heartbeat) and small chemical molecules, e.g. Na+, K+. These are not sufficient to provide in depth health information which requires sensing of large molecules such as proteins, ideally in real time, which is currently challenging. This provides a motivation to develop highly sensitive wearable biosensors for the detection of large molecules in sweat. This thesis centres on the development of a bio-material based wearable device for continuous detection of crucial analytes in human sweat. To achieve this target, our first aim was to design a highly bio-compatible flexible material as a substrate for wearable devices. A tough and anti-fouling three-network hydrogel has been prepared by integrating a zwitterionic polymer network into a robust double-network hydrogel. Secondly, to fill the gap between technological development of continuous and non-invasive detection of different analytes in human sweat, a patterned sweat-based biosensor was created for the detection of key biomolecules. This sensor was produced by placing specific aptamers or enzymes on flexible working electrodes. In addition, nanotechnology methods have been applied to refine the bio-sensing interface to further increase the sensitivity of our sensors. Finally, a sample collection chip has been combined with our high sensitivity sensors to fabricate a wearable device for sweat bio-sensing purposes. Future research may involve integration of a commercially available wireless signal readout module with this wearable biosensing device. The outcomes of this work may provide new insights for the development of wearable devices for continuous measurement of a spectrum of analytes in sweat, as an important step towards point-of-care diagnostics