Probing of Polymer Surfaces in the Viscoelastic Regime
Probing of Polymer Surfaces in the Viscoelastic Regime
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DOI：
10.1021/la404925h
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发表时间：
2014-09-09
期刊：
影响因子：
3.9
通讯作者：
Tsukruk, Vladimir V.
中科院分区：
文献类型：
--
作者：
Chyasnavichyus, Marius;Young, Seth L.;Tsukruk, Vladimir V.
本文讨论了目前广泛应用的原子力显微镜（AFM）在静态和动态环境下对高分子材料和生物材料的纳米力学性能进行表面探测的实验方法和建模方法，并分析了其局限性。为了方便这样的测量与最小化歧义，在这项研究中，我们提出了一种组合的方法来评估柔性聚合物材料的粘弹性特性。我们收集了一种基准聚合物材料（聚甲基丙烯酸正丁酯）在静态状态下的力距离数据，该材料在不同的加载速率和玻璃态、玻璃化过渡区和橡胶态的不同温度下，具有易于获得的玻璃化转变温度（约25摄氏度）。对于这一分析，我们利用了Johnson-modified Sneddons方法与标准线性实体模型相结合。对于稳健探测的关键实验步骤建议是：(i)使用具有良好特征的抛物线形状的尖端，（ii）在液体环境中探测以减少跳入现象，以及（iii）微小的压痕以确保没有塑性变形。虽然标准snedons模型在玻璃化过渡以下和以上都能产生足够的定量弹性模量值，但这种传统方法可能会显著低估玻璃化过渡区域附近（T-g以上或以下15℃）的实际模量值，主要偏差发生在损耗切线峰值处。通过对弹性区域（玻璃态和橡胶态）的snedons模型和粘弹性区域的Johnsons模型进行实验数据分析，可以恢复通用主曲线，并评估聚合物表面在玻璃过渡区域和相关加载速率下的存储模量、损耗模量、损耗切线、松弛时间和活化能。
In this Feature Article, we discussed the experimental and modeling methods and analyzed the limitations of the surface probing of nanomechanical properties of polymeric and biological materials in static and dynamic regimes with atomic force microscopy (AFM), which are widely utilized currently. To facilitate such measurements with minimized ambiguities, in this study we present a combined method to evaluate the viscoelastic properties of compliant polymeric materials. We collected forcedistance data in the static regime for a benchmark polymer material (poly(n-butyl methacrylate)) with an easily accessible glass-transition temperature (about 25 degrees C) at different loading rates and different temperatures across the glassy state, glass-transition region, and rubbery state. For this analysis, we exploited a Johnson-modified Sneddons approach in a combination with the standard linear solid model. Critical experimental steps suggested for robust probing are (i) the use of a tip with a well-characterized parabolic shape, (ii) probing in a liquid environment in order to reduce jump-in phenomenon, and (iii) minute indentations to ensure the absence of plastic deformation. Whereas the standard Sneddons model generates quantitatively adequate elastic modulus values below and above the glass transition, this traditional approach can significantly underestimate actual modulus values in the vicinity of the glass-transition region (15 degrees C above or below T-g), with major deviations occurring at the loss tangent peak. The analysis of the experimental data with Sneddons model for the elastic region (glassy and rubbery states) and Johnsons model for the viscoelastic region allowed for the restoration of the universal master curve and the evaluation of the storage modulus, loss modulus, loss tangent, relaxation times, and activation energies of the polymer surface across the glass-transition region and at relevant loading rates.