Institute of Physics, Montanuniversitaet Leoben, Franz Josef - Str. 18, 8700 Leoben, Austria.
Soft Matter. 2017 Dec 20;14(1):140-150. doi: 10.1039/c7sm02057k.
Viscoelastic properties are often measured using probe based techniques such as nanoindentation (NI) and atomic force microscopy (AFM). Rarely, however, are these methods verified. In this article, we present a method that combines contact mechanics with a viscoelastic model (VEM) composed of springs and dashpots. We further show how to use this model to determine viscoelastic properties from creep curves recorded by a probe based technique. We focus on using the standard linear solid model and the generalized Maxwell model of order 2. The method operates in the range of 0.01 Hz to 1 Hz. Our approach is suitable for rough surfaces by providing a defined contact area using plastic pre-deformation of the material. The very same procedure is used to evaluate AFM based measurements as well as NI measurements performed on polymer samples made from poly(methyl methacrylate) and polycarbonate. The results of these measurements are then compared to those obtained by tensile creep tests also performed on the same samples. It is found that the tensile test results differ considerably from the results obtained by AFM and NI methods. The similarity between the AFM results and NI results suggests that the proposed method is capable of yielding results comparable to NI but with the advantage of the imaging possibilities of AFM. Furthermore, all three methods allowed a clear distinction between PC and PMMA by means of their respective viscoelastic properties.
粘弹性性质通常使用基于探针的技术（如纳米压痕（NI）和原子力显微镜（AFM））进行测量。然而，这些方法很少得到验证。在本文中，我们提出了一种将接触力学与由弹簧和阻尼器组成的粘弹性模型（VEM）相结合的方法。我们进一步展示了如何使用该模型从基于探针的技术记录的蠕变曲线上确定粘弹性性质。我们专注于使用标准线性固体模型和二阶广义 Maxwell 模型。该方法在 0.01 Hz 至 1 Hz 的范围内运行。我们的方法通过使用材料的塑性预变形为粗糙表面提供定义的接触面积，因此适用于粗糙表面。同样的程序用于评估基于 AFM 的测量以及在由聚甲基丙烯酸甲酯（PMMA）和聚碳酸酯制成的聚合物样品上进行的 NI 测量。然后将这些测量的结果与在相同样品上进行的拉伸蠕变测试的结果进行比较。结果发现，拉伸测试结果与 AFM 和 NI 方法获得的结果有很大差异。AFM 结果与 NI 结果的相似性表明，所提出的方法能够产生与 NI 相当的结果，但具有 AFM 成像可能性的优势。此外，所有三种方法都通过其各自的粘弹性性质能够清楚地区分 PC 和 PMMA。
