Chen Shensheng, Olson Emily, Jiang Shan, Yong Xin
Department of Mechanical Engineering, Binghamton University, Binghamton, New York 13902, USA.
Nanoscale. 2020 Jul 21;12(27):14560-14572. doi: 10.1039/d0nr01740j. Epub 2020 Jul 2.
Mixing nanoparticles into a strategically selected polymer matrix yields nanocomposites with well-controlled microstructures and unique properties and functions. The modulation of nanoparticle assembly by polymer chain conformation can play a dominant role in determining nanocomposite structures, yet such a physical mechanism remains largely unexplored. We hypothesize that highly ordered microdomains of rigid linear polymers provide a template for nanoparticle assembly into open fractal structures. We conducted mesoscopic computer simulations and physical experiments to elucidate how polymer chain conformation regulates the dynamic evolution of nanoparticle structures during the drying processing of polymer nanocomposite films. The evaporation of polymer-nanoparticle mixtures with varying chain stiffnesses was simulated using dissipative particle dynamics. The formation of distinguished nanoparticle assemblies as a result of matrix selection was further corroborated by probing nanoparticle aggregation in different polymer nanocomposite coatings. The results show that polymer conformation not only influences the dispersion states of individual particles (dispersed vs. aggregated), but also modulates the morphologies of large-scale assembly (globular vs. fractal). The emergence of nematically ordered polymer clusters when the chain rigidity is increased creates local solvent-rich "voids" that promote anisotropic particle aggregates, which then percolate into open fractal structures upon solvent evaporation. The nanoparticle dynamics also exhibits an intriguing non-monotonic behavior attributed to the transitions between the coupling and decoupling with polymer dynamics. The nanoparticle assembly morphologies obtained in simulations match well with the electron microscopy images taken in physical experiments.
将纳米颗粒混入经过精心挑选的聚合物基体中，可得到具有微观结构可控、性质和功能独特的纳米复合材料。聚合物链构象对纳米颗粒组装的调制在决定纳米复合材料结构方面可能起主导作用，但这种物理机制在很大程度上仍未得到探索。我们假设刚性线性聚合物的高度有序微区为纳米颗粒组装成开放分形结构提供了模板。我们进行了介观计算机模拟和物理实验，以阐明在聚合物纳米复合薄膜干燥过程中，聚合物链构象如何调节纳米颗粒结构的动态演变。使用耗散粒子动力学模拟了具有不同链刚度的聚合物 - 纳米颗粒混合物的蒸发过程。通过探测不同聚合物纳米复合涂层中的纳米颗粒聚集情况，进一步证实了由于基体选择而形成的独特纳米颗粒组装。结果表明，聚合物构象不仅影响单个颗粒的分散状态（分散与聚集），还调节大规模组装的形态（球状与分形）。当链刚度增加时，向列有序聚合物簇的出现会产生局部富溶剂的“空隙”，促进各向异性颗粒聚集体的形成，这些聚集体在溶剂蒸发时会渗透成开放的分形结构。纳米颗粒动力学还表现出一种有趣的非单调行为，这归因于与聚合物动力学之间耦合和解耦的转变。模拟中获得的纳米颗粒组装形态与物理实验中拍摄的电子显微镜图像非常吻合。
