Materials and Manufacturing Directorate , Air Force Research Laboratory , Wright-Patterson Air Force Base , Ohio 45433 , United States.
UES Inc. , 4401 Dayton Xenia Road , Beavercreek , Ohio 45432 , United States.
ACS Appl Mater Interfaces. 2018 Dec 19;10(50):43865-43873. doi: 10.1021/acsami.8b12965. Epub 2018 Dec 7.
The thermal reshaping of gold nanorods in a polymer matrix is an important phenomenon for many potential applications. However, a fundamental understanding of the various mechanisms that govern the nanorod reshaping dynamics is still lacking. Here, we provide evidence for a phenomenological model of the gold nanorod shape transformation based on the measurements and detailed analysis of the time-resolved thermal reshaping for a variety of gold nanorods having different geometries (aspect ratio, volume, diameter) in a cross-linked epoxy matrix at application relevant temperatures (120-220 °C). Our analysis suggests that (a) the nanorod reshaping dynamics consist of two temporal regimes that are governed by different phenomena and (b) the ultimate amount of reshaping at a given temperature depends strongly on the initial particle geometry and the mechanical stiffness of its surroundings. At short times, the shape transformation is dominated by a curvature-induced surface diffusion process, in which the activation energy for diffusion depends on curvature. At long times, however, the surrounding environment plays a key role in slowing the diffusion and stabilizing the nanorod shape. We show that the long-time behavior can be well described using a modified surface diffusion model that takes into account the slowing of atomic diffusivity as a result of external forces arising from mechanical constraints. The ability to tune both the final shape and the reshaping dynamics in nanocomposites opens up new possibilities in tailoring the optical properties of these materials.
聚合物基体中金纳米棒的热重塑是许多潜在应用的重要现象。然而，对于控制纳米棒重塑动力学的各种机制，仍然缺乏基本的理解。在这里，我们提供了一种基于对各种不同形状（纵横比、体积、直径）的金纳米棒在交联环氧树脂基体中的时间分辨热重塑的测量和详细分析的金纳米棒形状转变的唯象模型的证据，这些金纳米棒在应用相关温度（120-220°C）下进行测量。我们的分析表明：（a）纳米棒重塑动力学由两个不同现象控制的时间域组成；（b）在给定温度下的最终重塑量强烈取决于初始颗粒的几何形状及其周围环境的机械刚度。在短时间内，形状转变由曲率诱导的表面扩散过程主导，其中扩散的激活能取决于曲率。然而，在长时间内，周围环境在减缓扩散和稳定纳米棒形状方面起着关键作用。我们表明，长时间行为可以通过考虑由于机械约束引起的外力导致的原子扩散率减慢的改进的表面扩散模型来很好地描述。在纳米复合材料中同时调整最终形状和重塑动力学的能力为这些材料的光学性质的调整开辟了新的可能性。
