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Title: Performance of The Quartz Crystal Microbalance in Liquid Environment
Keywords: Quartz Crystal Microbalance, Contact Angle, Viscoelasticity, Iinterfacial Slip, Compressional Wave, Colloid Suspension
Issue Date: 19-Jul-2011
Citation: ZHUANG HAN (2011-07-19). Performance of The Quartz Crystal Microbalance in Liquid Environment. ScholarBank@NUS Repository.
Abstract: A quartz crystal microbalance (QCM) is extended to be operated in contact with droplets of various liquids including aqueous solutions, silicone oils and colloidal suspensions, which has demonstrated the capability of the droplet-based QCM of monitoring wetting or evaporation phenomena. The conventional application of the QCM is microgravimetry which is based on the Sauerbrey equation. However, the Sauerbrey equation uncovers the possible influence of the surface stress due to adsorption. In this thesis, it is recognized that when the QCM is miniaturized, the effect of the adsorption induced surface stress may come into play, distorting the microweighing results. Besides microweighing, it is recognized that the QCM can be operated in contact with droplets as a high-frequency interfacial rheometer for characterization of the liquid properties. However, there are still experimental and theoretical challenges left for the droplet-based QCM. In this thesis, we are mainly concerned with investigating a variety of nongravimetric effects arising from the dynamic contact angle between the droplet and the substrate, the viscoelastic properties of the liquids, the interfacial slippage and the coupled compressional waves. It is found that the proposed models can be mechanisms to interpret the reported experimental results, which have shown the abnormal increments in the resonant frequency when the QCM is operated in contact with droplets of silicone oils. Another example of the nongravimetric application of the QCM in contact with droplets is to monitor the evaporation of droplets of colloidal suspensions. In this work, alumina colloidal suspensions with varying solid concentration and particle size are tested, and the experimental results are evaluated by the proposed models in terms of the contact stiffness. On the theoretical side, it is shown that the contact stiffness which relies on different inter-particle interactions is likely to play a role in quantifying the measured quantities in the contact mechanics studies with the droplet-based QCM. The theoretical and experimental work in this thesis should deepen our understanding of the QCM in contact with droplets, and the ensuing discussions may contribute much to the increasing interest in applications of the droplet-based QCM as bio-sensors in life science.
Appears in Collections:Ph.D Theses (Open)

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