Analysis Of The Response Of Quartz Crystal Microbalance In Studying The Process Of Adsorption And Properties Of Adsorbed Film On The Interface

Quartz crystal microbalance with dissipation(QCM-D) is a new type of mass sensor with very high sensitivity:its resonant frequency shift can detect the mass change of nano-gram of adsorbed film or solution near the quartz crystal surface,and D factor characterizes the energy dissipation in them.The combination of these two parameters allow accurate measurement of mass,viscosity and shear modulus of materials near the surface,so it is widely used in many fields,such as the surface analysis of bio-materials,the interactions between bio-macromolecules,adsorption and desorption of bio-macromolecules and cell,the properties of adsorbed film and the atomic friction.Because the measurement results are influenced by many factors, there are some difficult in quantitative analysis,most times it is used to do the qualitative research.In this thesis,we detailed discussed the influence of concerned parameters,for example,mass,thickness,viscoelastic properties,adsorption isotherm, on the resonant frequency shift and dissipation factor,and got some meaningful results as follows:1,based on the Voight model,we got the expressions of resonant frequency shift and dissipation factor of infinite adsorbed layer by mathematical induction.This makes the research of the effect of density profile on measurement results possible; and we give the expressions of resonant frequency shift and dissipation factor under many different conditions.2,we carried out the simulation of the influence of viscoelastic and density profile on the resonant frequency shift and dissipation factor,and the influence of density profile on film resonance,under the assumption of single adsorbed film with constant mass.The simulation results show that the incremental ratio of resonant frequency decrease as the increases of viscosity,and reaches the plateau quickly;the resonant frequency shift is not affected by shear modulus;the dissipation factor is proportional to the shear modulus;the density profile has big impact on the resonant frequency shift,the magnitude of this impact depends on the viscosity of the first layer which is closest to the quartz surface;the magnitude of film resonance can be weaken by the change of density profile.3,we studied the influence of solution and parameters such as adsorption constant,viscosity/shear modulus-concentration coefficient on the measurement of QCM under Langmuir adsorption model.The results display that for resonant frequency shift,the contribution from the solution is bigger than adsorbed film if the solution is concentrated,so the adsorption behavior studied by quartz crystal microbalance should be done under dilute solution;the feature of resonant frequency shift isotherm is similar to adsorption isotherm,except that the frequency shift isotherm approaches saturated value quicker than adsorption isotherm,and the bigger viscosity/shear modulus/adsorption constant under the same concentration is,the quicker to the saturated;the dissipation increase and then decrease as the beginning and the end of the adsorption,indicating the adsorbed film turns to rigid layer as the increase of adsorbed molecule number.4,we investigated the influence of viscoelastic properties and layer number of adsorbed film on the resonant frequency shift and dissipation factor.The results here and in step 3 are alike:the resonant frequency shift isotherm has the similar features with adsorption isotherm.This conclusion implies that the quartz crystal microbalance can be used to study the adsorption behavior,interaction between adsorbed molecules and the density profile.5,we compared the applications of quartz crystal microbalance and surface plasmon resonance in studying the properties of adsorbed film.The simulation results reveal that SPR technique exactly gives the value of adsorbed mass and is independent of density profile of adsorbed film,while QCM technique gives the value of adsorbed mass with coupled water,contain more information such as structure, viscosity,shear modulus,etc,and is independent of adsorbed mass if the viscoelastic of layer is much bigger than the solution.This confirms the conclusion:the QCM technique is sensitive to extended,water-rich layer,SPR technique is sensitive to compact,dense layer.So SPR can be used to detect the mass change and QCM can be used to detect the conformation change near the surface.6,we analysis the adsorption behavior of PNIPAM on the solid-liquid interface and viscoelastic properties of PEG solution near the surface based on the experimental results probed by quartz crystal microbalance.The results show that QCM is a powerful tool in studying the adsorption behavior and properties of molecules on the interface.