Dynamic AFM on Viscoelastic Polymer Samples with Surface Forces
Dynamic AFM on Viscoelastic Polymer Samples with Surface Forces
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DOI：
10.1021/acs.macromol.8b01485
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发表时间：
2018-12-11
期刊：
影响因子：
5.5
通讯作者：
Raman, Arvind
中科院分区：
文献类型：
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作者：
Rajabifar, Bahram;Jadhav, Yoti M.;Raman, Arvind
动态原子力显微镜（dAFM）广泛用于表征空气/真空环境下聚合物粘弹性表面；然而，仪器观测值（如能量耗散或相对比）与聚合物表面纳米级物理性质（如局部粘弹性、弛豫和粘附性）之间的联系仍然知之甚少。为了阐明这一主题，我们提出了一种计算方法，可以用第一性原理方法预测和解释具有任意表面力和线性粘弹性本构性的样品上的dAFM观测值。该方法既加速了Attard引入的计算方法，又将其嵌入到分接模式减幅公式（或相当于调频频移/阻尼公式）中，以恢复力历史和仪器观测值作为设定点振幅或Z距离的函数。该方法与其他可靠的计算代码进行了验证。澄清了表面力和聚合物弛豫时间对相滞后、能量耗散和表面变形历史的作用。在由分散良好的聚丙烯、聚碳酸酯和弹性体组成的三聚合物共混物上，给出了不同自由振幅和设定值比下攻丝模式/振幅调制AFM （TM-AFM/AM-AFM）能量耗散的实验数据。提出并分析了一种对计算结果进行实验验证的方法。
Dynamic atomic force microscopy (dAFM) is widely used to characterize polymer viscoelastic surfaces in the air/vacuum environments; however, the link between the instrument observables (such as energy dissipation or phase contrast) and the nanoscale physical properties of the polymer surfaces (such as local viscoelasticity, relaxation, and adhesion) remains poorly understood. To shed light on this topic, we present a computational method that enables the prediction and interpretation of dAFM observables on samples with arbitrary surface forces and linear viscoelastic constitutive properties with a first-principles approach. The approach both accelerates the computational method introduced by Attard and embeds it within the tapping mode amplitude reduction formula (or, equivalently, frequency modulation frequency shift/damping formula) to recover the force history and instrument observables as a function of the set point amplitude or Z distance. The method is validated against other reliable computational codes. The role of surface forces and polymer relaxation times on the phase lag, energy dissipation, and surface deformation history is clarified. Experimental data on energy dissipation in tapping mode/amplitude modulation AFM (TM-AFM/AM-AFM) for different free amplitudes and set point ratios are presented on a three-polymer blend consisting of well-dispersed phases of polypropylene, polycarbonate, and elastomer. An approach to experimental validation of the computational results is presented and analyzed.