【作者】 方佳节；

【导师】 朱大鸣；

【作者基本信息】 中国科学技术大学 ， 物理电子学， 2009， 博士

【摘要】 石英晶体微天平(quartz crystal microbalance with dissipation,QCM-D)是一种灵敏度极高的传感器,其共振频率的变化(△f)可以精确测量石英晶体表面溶液或吸附膜纳克量级的质量变化,D因子表征能量在其中的耗散。两者的结合,可以测量石英晶体表面物质的质量、粘度、剪切模量等参数,因此被广泛应用于化学、生物、医学、物理等领域,如生物材料的表面分析、生物大分子的相互作用、生物大分子/细胞的吸附和解吸附、纳米尺度吸附膜的粘弹性、原子尺度下的摩擦力等方面的研究。由于测量结果只有共振频率的变化和D因子两个参数,而实验中所涉及的各种物理参数又比较多,因此定量分析比较困难,多用于定性研究。围绕测量中涉及的各种因素对实验结果的影响,本论文开展了大量的研究,取得的主要成果如下:1,在Voight模型的基础上,利用数学归纳法,推导出无穷层吸附膜△f和△D的表达式,使得研究密度分布对实验结果的影响成为可能;给出多种条件下△f和△D的表达式。2,在单层吸附膜的情况下,假定质量恒定,研究吸附膜粘弹性和密度分布对△f和△D的影响,并研究密度分布对film resonance的影响。结果显示:△f的变化随粘度的增加而迅速变化,然后达到一个稳定值;剪切模量与粘度、角频率的乘积之比值小于0.1时,剪切模量对△f无影响;剪切模量继续增加,共振频率的变化略有增加;D因子的数值正比于剪切模量:密度分布对△f有巨大的影响,且界面处的粘度越大,密度分布对△f的影响越大;film resonance可以通过形态的变化而减弱。3,在Langmuir吸附模型下,分析溶液、吸附常数、粘度/剪切模量-浓度关系等参数对实验结果的影响。结果指出,浓溶液对测量结果的干扰巨大,因此吸附行为的研究只能在低浓度下进行;△f的变化与吸附等温线有相似的变化规律;相同浓度下,粘度、剪切模量、吸附常数越大,共振频率的变化数值越早到达稳定值;D因子先增加后减小,表明随着吸附分子数目的增加,吸附膜趋于刚性,且D因子的最大值,与吸附膜的剪切模量有关。4,在BET吸附模型下,分析粘弹性、吸附层数对△f和△D的影响。结论如3,△f与吸附等温线有相同的变化规律:每一层吸附的开始阶段,△D迅速增大;随吸附逐渐完成,△D迅速减小。3、4的结果表明,石英晶体微天平可以用于各种分子的吸附行为、相互作用、形态变化等的研究。5,对比分析了QCM-D和表面等离子体共振仪(Surface Plasmon Resonance,SPR)在测量吸附膜性质方面的应用。计算结果验证了这样的事实:QCM-D适用于含水较多的、伸展的吸附膜的研究,给出的是质量、粘弹性的综合结果,因此一般来说QCM-D给出的质量偏大;SPR适用于紧凑、密集的吸附膜的研究,精确给出质量。因此,QCM-D的测量结果更复杂,包含了更多的信息,如吸附过程中吸附膜形态的变化、吸附膜的粘度、剪切模量等。因此QCM-D测量结果的定量分析比较困难。6,在上述计算结果和实验的基础上,分析了PNIPAM分子的吸附行为,以及界面处PEG溶液的粘弹性随浓度的变化。分析结果表明,QCM是研究吸附行为和界面处溶液性质的强有力工具。更多还原

【Abstract】 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.更多还原