Acquirement Of Electrical Parameters Of Quartz Crystal Microbalance And Its Application In Physisorption

Quartz Crystal Microbalance (QCM) is a new type of micro-mass sensor which allows accurate measurements of mass, viscosity and shear modulus on nano-scale. It has been used widely in many fields, such as electrochemistry, biomedicine, organic chemistry, analytical chemistry, physics, etc, because of its high precision, good stability, small size and simple structure. In this thesis, we extensively discussed the basic principle, theoretical model, driving and interface circuit, measurement of network analyzer, application on physisorption of QCM. We presented the simulating calculation about the influence of physical properties on measurable results. The design of hardware and software of the data-acquisition system of QCM was introduced. The implementation of network analyzer on QCM measurements was proposed. Also we got some interesting results about the physisorption of macromolecule on solid surface.In our research, we did something new as follows:1) Based on the mechanical and electrical model we carried out a series of simulation on the electrical response of QCM. The result shows that the viscoelastic properties of adsorption films and solution have a large impact on the measurable result of QCM. We calculated the determinate errors which were brought by the solution when quartz acted as the mass sensor.2) We analysed the important and difficult points of the driving circuit of QCM and proposed a new design of driving circuit which can measure frequency, resistance and dissipation. An intellectual temperature controllable system was designed to satisfy the rigorous demand of temperature stability.3) We designed a high speed data-acquisition circuit of QCM with USB2.0 interface. It adopts the technique of high speed and high precision A/D converter and frequency measurement with equal-precision. It has two analog channels and can be used in many scientific and commercial fields.4) We built a system in order to determine the parameters of QCM based on network analyzer. It can measure the electrical parameters of QCM at different harmonics. It can work under extremely lossy circumstances and can be used together with the general QCM apparatus.5) We carried out the experiments of physisorption of PNIPAM on gold surface by QCM. The results suggest that the adsorption of PNIPAM is strongly influenced by the conformation of the polymer. The adsorption kinetics in the swollen state is governed by molecular diffusion to the adsorption substrate; the adsorption time constant depends strongly on concentration and temperature. The time constant for PNIPAM in the collapsed state is nearly temperature- and concentration-independent. In the concentration range below 100 ppm in weight, only a monolayer of PNIPAM in the swollen state can form on the gold electrode surface of QCM. As the polymer transforms to the collapsed state, multilayer PNIPAM forms on the same substrate.