Quantitative Rheometry of Thin Soft Materials Using the Quartz Crystal Microbalance with Dissipation
Quantitative Rheometry of Thin Soft Materials Using the Quartz Crystal Microbalance with Dissipation
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DOI：
10.1021/acs.analchem.7b05423
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发表时间：
2018-03-20
影响因子：
7.4
通讯作者：
Vogt, Bryan D.
中科院分区：
文献类型：
--
作者：
Sadman, Kazi;Wiener, Clinton G.;Vogt, Bryan D.
在惯性极限下，石英晶体微量天平（QCM）的谐振频率与石英传感器上的耦合质量有关，通过Sauerbrey表达式将质量与谐振频率的变化联系起来。然而，当膜的厚度足够大时，关系变得更加复杂，并且必须考虑晶体谐振的频率和阻尼。在这种情况下，必须使用材料的流变模型来从数据中准确地提取粘附膜的厚度、剪切模量和粘弹性相位角。在本工作中，我们研究了两种粘弹性模型的适用性，一种是简单的Voigt模型（Physica Scripta 1999，59，391-396），另一种是更现实的幂律模型（Langmuir 2015，31，4008-4017），以提取温敏水凝胶膜的流变特性。通过改变温度和凝胶的初始干膜厚度，QCM的操作从Sauerbrey极限（其中粘性损失不影响频率）穿过QCM响应对粘弹性性质敏感的区域。当剪切波长比d/lambda（n）在0.05-0.20范围内时，两种模型的密度剪切模量和粘弹性相位角吻合得很好，其中d是薄膜厚度，lambda（n）是机械剪切波在n次谐波处的波长。我们进一步提供了一个框架，用于估计软材料的物理性质，在兆赫制度，通过使用的物理行为的复合物。这为用户提供了一个近似的允许薄膜厚度范围，用于精确的粘弹性分析，从而使QCM-D更好地用于软材料研究。
In the inertial limit, the resonance frequency of the quartz crystal microbalance (QCM) is related to the coupled mass on the quartz sensor through the Sauerbrey expression that relates the mass to the change in resonance frequency. However, when the thickness of the film is sufficiently large, the relationship becomes more complicated and both the frequency and damping of the crystal resonance must be considered. In this regime, a rheological model of the material must be used to accurately extract the adhered film's thickness, shear modulus, and viscoelastic phase angle from the data. In the present work we examine the suitability of two viscoelastic models, a simple Voigt model (Physica Scripta 1999, 59, 391-396) and a more realistic power-law model (Langmuir 2015, 31, 4008-4017), to extract the rheological properties of a thermoresponsive hydrogel film. By changing temperature and initial dry film thickness of the gel, the operation of QCM was traversed from the Sauerbrey limit, where viscous losses do not impact the frequency, through the regime where the QCM response is sensitive to viscoelastic properties. The density-shear modulus and the viscoelastic phase angle from the two models are in good agreement when the shear wavelength ratio, d/lambda(n), is in the range of 0.05-0.20, where d is the film thickness and lambda(n) is the wavelength of the mechanical shear wave at the nth harmonic. We further provide a framework for estimating the physical properties of soft materials in the megahertz regime by using the physical behavior of polyelectrolyte complexes. This provides the user with an approximate range of allowable film thicknesses for accurate viscoelastic analysis with either model, thus enabling better use of the QCM-D in soft materials research.