Nguyen Hung K, Pittenger Bede, Nakajima Ken
Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan.
Bruker Nano Surfaces, AFM Unit, Santa Barbara, California 93117, United States.
Nano Lett. 2024 Jul 31;24(30):9331-9336. doi: 10.1021/acs.nanolett.4c02261. Epub 2024 Jul 17.
Understanding the evolution of local structure and mobility of disordered glassy materials induced by external stress is critical in modeling their mechanical deformation in the nonlinear regime. Several techniques have shown acceleration of molecular mobility of various amorphous glasses under macroscopic tensile deformation, but it remains a major challenge to visualize such a relationship at the nanoscale. Here, we employ a new approach based on atomic force microscopy in nanorheology mode for quantifying the local dynamic responses of a polymer glass induced by nanoscale compression. By increasing the compression level from linear elastic to plastic deformation, we observe an increase in the mechanical loss tangent (tan δ), evidencing the enhancement of polymer mobility induced by large stress. Notably, tan δ images directly reveal the preferential effect of the large compression on the dynamic acceleration of nanoscale heterogeneities with initially slow mobility, which is clearly different from that induced by increasing temperature.
理解外部应力引起的无序玻璃态材料局部结构和流动性的演变对于模拟其在非线性状态下的机械变形至关重要。几种技术已表明，在宏观拉伸变形下，各种非晶态玻璃的分子流动性会加速，但在纳米尺度上可视化这种关系仍然是一个重大挑战。在此，我们采用一种基于纳米流变模式下原子力显微镜的新方法，来量化纳米尺度压缩引起的聚合物玻璃的局部动态响应。通过将压缩水平从线性弹性增加到塑性变形，我们观察到机械损耗角正切（tan δ）增加，这证明了大应力引起的聚合物流动性增强。值得注意的是，tan δ图像直接揭示了大压缩对初始流动性较慢的纳米尺度不均匀性动态加速的优先影响，这与升温引起的影响明显不同。
