Division of Multiscale Mechanical Design, School of Mechanical and Aerospace Engineering, Seoul National University , San 56-1, Shillim-Dong, Kwanak-Ku, Seoul151-744, Korea.
ACS Appl Mater Interfaces. 2016 Sep 14;8(36):24008-24. doi: 10.1021/acsami.6b04818. Epub 2016 Aug 30.
We investigated the optical and thermal actuation behavior of densely cross-linked photoresponsive polymer (PRP) and polymer nanocomposites containing gold nanoparticles (PRP/Au) using all-atom molecular dynamics (MD) simulations. The modeled molecular structures contain a large number of photoreactive mesogens with linear orientation. Flexible side chains are interconnected through covalent bonds under periodic boundary conditions. A switchable dihedral potential was applied on a diazene moiety to describe the photochemical trans-to-cis isomerization. To quantify the photoinduced molecular reorientation and its effect on the macroscopic actuation of the neat PRP and PRP/Au materials, we characterized the photostrain and other material properties including elastic stiffness and thermal stability according to the photoisomerization ratio of the reactive groups. We particularly examined the effect of nanoparticle size on the photothermal actuation by varying the diameter of the nanofiller (10-20 Å) under the same volume fraction of 1.62%. The results indicated that the insertion of the gold nanoparticles enlarges the photostrain of the material while enhancing its mechanical stiffness and thermal stability. When the diameter of the nanoparticle reaches a size similar to or smaller than the length of the mesogen, the interfacial energy between the nanofiller and the surrounding polymer matrix does not significantly affect the alignment of the mesogens, but rather the adsorption energy at the interface generates a stable interphase layer. Hence, these improvements were more effective as the size of the gold nanoparticle decreased. The present findings suggest a wider analysis of the nanofiller-reinforced PRP composites and could be a guide for the mechanical design of the PRP actuator system.
我们使用全原子分子动力学 (MD) 模拟研究了含有金纳米粒子 (PRP/Au) 的致密交联光响应聚合物 (PRP) 和聚合物纳米复合材料的光学和热致动行为。所模拟的分子结构包含大量具有线性取向的光反应介晶。柔性侧链在周期性边界条件下通过共价键相互连接。在 diazene 部分应用可切换的二面角势来描述光化学的反式-顺式异构化。为了量化光致分子重取向及其对纯 PRP 和 PRP/Au 材料宏观致动的影响，我们根据反应基团的光异构化比例来表征光致应变和其他材料特性，包括弹性刚度和热稳定性。我们特别通过改变纳米填料的直径（10-20Å）来研究纳米颗粒尺寸对光致热致动的影响，在相同的体积分数为 1.62%的情况下。结果表明，金纳米粒子的插入会增大材料的光致应变，同时提高其机械刚度和热稳定性。当纳米粒子的直径达到与介晶长度相似或更小的尺寸时，纳米填料和周围聚合物基质之间的界面能不会显著影响介晶的取向，而是界面处的吸附能会产生一个稳定的相间层。因此，随着金纳米粒子尺寸的减小，这些改进变得更加有效。本研究结果表明，对纳米粒子增强的 PRP 复合材料进行更广泛的分析，并可为 PRP 致动器系统的机械设计提供指导。
