Zhu Yuwen, Giuntoli Andrea, Zhang Wengang, Lin Zhongqin, Keten Sinan, Starr Francis W, Douglas Jack F
State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China.
Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands.
J Chem Phys. 2022 Sep 7;157(9):094901. doi: 10.1063/5.0101551.
The introduction of soft organic nanoparticles (NPs) into polymer melts has recently expanded the material design space for polymer nanocomposites, compared to traditional nanocomposites that utilize rigid NPs, such as silica, metallic NPs, and other inorganic NPs. Despite advances in the fabrication and characterization of this new class of materials, the effect of NP stiffness on the polymer structure and dynamics has not been systematically investigated. Here, we use molecular dynamics to investigate the segmental dynamics of the polymer interfacial region of isolated NPs of variable stiffness in a polymer matrix. When the NP-polymer interactions are stronger than the polymer-polymer interactions, we find that the slowing of segmental dynamics in the interfacial region is more pronounced for stiff NPs. In contrast, when the NP-polymer interaction strength is smaller than the matrix interaction, the NP stiffness has relatively little impact on the changes in the polymer interfacial dynamics. We also find that the segmental relaxation time τ of segments in the NP interfacial region changes from values lower than to higher than the bulk material when the NP-polymer interaction strength is increased beyond a "critical" strength, reminiscent of a binding-unbinding transition. Both the NP stiffness and the polymer-surface interaction strength can thus greatly influence the relative segmental relaxation and interfacial mobility in comparison to the bulk material.
与利用刚性纳米粒子（如二氧化硅、金属纳米粒子和其他无机纳米粒子）的传统纳米复合材料相比，将软有机纳米粒子（NPs）引入聚合物熔体最近扩展了聚合物纳米复合材料的材料设计空间。尽管这类新材料在制备和表征方面取得了进展，但纳米粒子刚度对聚合物结构和动力学的影响尚未得到系统研究。在此，我们使用分子动力学来研究聚合物基体中具有可变刚度的孤立纳米粒子的聚合物界面区域的链段动力学。当纳米粒子与聚合物的相互作用强于聚合物与聚合物的相互作用时，我们发现刚性纳米粒子在界面区域的链段动力学减慢更为明显。相比之下，当纳米粒子与聚合物的相互作用强度小于基体相互作用时，纳米粒子刚度对聚合物界面动力学变化的影响相对较小。我们还发现，当纳米粒子与聚合物的相互作用强度增加超过“临界”强度时，纳米粒子界面区域链段的链段弛豫时间τ从低于本体材料的值变为高于本体材料的值，这让人联想到结合-解离转变。因此，与本体材料相比，纳米粒子刚度和聚合物-表面相互作用强度都能极大地影响相对链段弛豫和界面迁移率。
