Soft, Structured Layers on the Surface of a Quartz Crystal Microbalance (QCM): A Computational Model to Predict Shifts of Frequency and Bandwidth Based on the Lattice-Boltzmann Method

石英晶体微天平 (QCM) 表面的软结构化层：基于格子-玻尔兹曼方法预测频率和带宽变化的计算模型

• 批准号: 324062370
• 负责人: Professor Dr.-Ing. Gunther Brenner
• 金额: --
• 依托单位: Institut für Physikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/324062370?language=en
• 关键词: Soft; Structured; Layers; Surface; Quartz

Building on a linearized variant of the Lattice Boltzmann Method (termed Frequency-Domain Lattice-Boltzmann Method), a simulation package shall be developed, which models the behavior a quartz crystal microbalance (QCM) in contact with structured samples in the liquid phase. While the method shall be applicable to samples with arbitrary shape, this work shall focus on particulate adsorbates with a thickness much below the wavelength of sound (such adsorbed globular proteins). Among the parameters to be varied is the coverage. The parameters to be predicted are the shifts of resonance frequency and resonance bandwidth on the different overtones of the resonator. Analytical models predicting these parameters exist for planar layer systems, but not for laterally heterogeneous samples. A first step shall be to quantify the contribution of the liquid mass trapped between adsorbed particles to the overall apparent mass, where the latter is calculated from the frequency shift with the (very simple) Sauerbrey equation. Particles of variable size, shape, and orientation shall be randomly deposited on the resonator surface, where the algorithm doing so shall allow for clustering. A second step shall be to study the consequences of a finite compliance of the contact between the particle and the substrate. Finite compliance is expected to increase the resonance bandwidth. This expectation shall be tested and be turned into a quantitative prediction. Strategies for inversion shall be identified: For certain configurations of practical importance, rules shall be derived, which allow to infer parameters of the sample (such as the average height of the particles, the stiffness of link, or the degree of clustering) from the experimentally determined values as a function of overtone order and coverage. Later in the project, the code shall be improved with regard to the accuracy, by which the forces at the particle surfaces are obtained. This step will be important for the study of adsorbates with sizes comparable to the wavelength of sound. For the current code, such layers pose a technical problem, which can be circumvented if the layers are acoustically thin. Adsorbed particles with a thickness of the order of the wavelength of sound often display so-called coupled resonances. Coupled resonances can be viewed as adsorption lines in shear-wave spectroscopy. There is a far-reaching analogy to vibrational spectroscopy on molecules. In particular, there is a mode-assignment problem, meaning that a coupled resonance can be caused by different modes of motion of the adsorbed object. The mode assignment problem shall be solved by the proposed work. In particular, it shall be clarified for a given experimental example, whether the coupled resonance is caused by a rocking mode, which exerting a bending stress at the link, or a slipping mode which exerts a tangential stress.

基于晶格玻尔兹曼方法的线性化变体（称为频域晶格玻尔兹曼方法），应开发模拟包，模拟石英晶体微天平（QCM）与液相结构化样品接触的行为。虽然该方法应适用于任意形状的样品，但这项工作应侧重于厚度远低于声波波长的颗粒吸附物（如吸附的球状蛋白质）。要改变的参数之一是覆盖率。待预测的参数是谐振频率和谐振带宽在谐振器的不同泛音上的偏移。分析模型预测这些参数存在的平面层系统，但不横向异质样品。第一步应量化吸附颗粒之间捕获的液体质量对总表观质量的贡献，后者是通过（非常简单的）Sauerbrey方程从频移计算的。可变尺寸、形状和方向的颗粒应随机沉积在谐振器表面上，这样做的算法应允许聚类。第二步是研究颗粒和基体之间接触的有限柔度的结果。有限的顺应性预期会增加谐振带宽。这一预期将得到检验，并转化为定量预测。应确定反演的策略：对于具有实际重要性的某些配置，应推导出规则，这些规则允许从实验确定的值推断样品的参数（例如颗粒的平均高度、连接的刚度或聚类的程度），作为泛音顺序和覆盖的函数。在项目后期，应在精度方面改进代码，通过该代码获得颗粒表面的力。这一步骤对于研究大小与声波波长相当的吸附物将是重要的。对于当前的规范，这样的层提出了一个技术问题，如果这些层在声学上很薄，则可以规避这个问题。具有声波波长量级厚度的吸附颗粒经常显示出所谓的耦合共振。耦合共振可以看作是剪切波光谱中的吸附线。这与分子的振动光谱有着深远的相似性。特别是，有一个模式分配的问题，这意味着耦合共振可以由不同的吸附对象的运动模式。模式分配问题应通过拟议工作解决。特别地，对于给定的实验示例，应当澄清耦合共振是由在连杆处施加弯曲应力的摇摆模式引起的，还是由施加切向应力的滑动模式引起的。