Collective Nanoparticle Dynamics Associated with Bridging Network Formation in Model Polymer Nanocomposites
Collective Nanoparticle Dynamics Associated with Bridging Network Formation in Model Polymer Nanocomposites
复制标题
与模型聚合物纳米复合材料中桥接网络形成相关的集体纳米粒子动力学
DOI：
10.1021/acsnano.1c01283
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发表时间：
2021
期刊：
影响因子：
17.1
通讯作者：
Schweizer, Kenneth S.
中科院分区：
文献类型：
--
作者：
Yavitt, Benjamin M.;Salatto, Daniel;Zhou, Yuxing;Huang, Zhixing;Endoh, Maya;Wiegart, Lutz;Bocharova, Vera;Ribbe, Alexander E.;Sokolov, Alexei P.;Schweizer, Kenneth S.
在聚合物中加入纳米粒子是改善高分子材料力学性能和其他性能的一种有效方法。这种聚合物-粒子混合系统也具有丰富的基础软物质物理。在促进机械增强的几个因素中，聚合物介导的NP网络被认为是聚合物纳米复合材料（pnc）中最重要的。本文利用x射线光子相关光谱学和微观统计力学理论对模型pnc中的集体NP动力学进行了综合实验-理论研究。二氧化硅NPs分散在未纠缠或纠缠的聚（2-乙烯基吡啶）矩阵在一系列的NP负载被使用。在高于体玻璃化转变温度的温度下，NP子系统的静态集体结构因子揭示了在高于渗透阈值的高NP负载下，聚合物介导的网状微结构桥的形成。NP集体弛豫时间比孤立NP的自扩散极限长3个数量级，并与观测波矢量和NP载荷密切相关。模式耦合理论动力学分析，结合静态聚合物介导的桥接结构和集体运动的NPs进行。它很好地捕获了未纠缠聚合物基体中集体NP动力学的散射波矢量和NP负载依赖关系，并且在纠缠的PNC样品中出现了适度的定量偏差。此外，我们确定了一个不寻常的和弱的温度依赖集体NP动力学，在定性对比机械响应。因此，本研究揭示了由聚合物桥连接的NPs与粘性吸附聚合物介质接触时集体运动的关键方面，并确定了对这些复杂软材料的理论理解的一些突出的挑战。
The addition of nanoparticles (NPs) to polymers is a powerful method to improve the mechanical and other properties of macromolecular materials. Such hybrid polymer–particle systems are also rich in fundamental soft matter physics. Among several factors contributing to mechanical reinforcement, a polymer-mediated NP network is considered to be the most important in polymer nanocomposites (PNCs). Here, we present an integrated experimental–theoretical study of the collective NP dynamics in model PNCs using X-ray photon correlation spectroscopy and microscopic statistical mechanics theory. Silica NPs dispersed in unentangled or entangled poly(2-vinylpyridine) matrices over a range of NP loadings are used. Static collective structure factors of the NP subsystems at temperatures above the bulk glass transition temperature reveal the formation of a network-like microstructureviapolymer-mediated bridges at high NP loadings above the percolation threshold. The NP collective relaxation times are up to 3 orders of magnitude longer than the self-diffusion limit of isolated NPs and display a rich dependence with observation wavevector and NP loading. A mode-coupling theory dynamical analysis that incorporates the static polymer-mediated bridging structure and collective motions of NPs is performed. It captures well both the observed scattering wavevector and NP loading dependences of the collective NP dynamics in the unentangled polymer matrix, with modest quantitative deviations emerging for the entangled PNC samples. Additionally, we identify an unusual and weak temperature dependence of collective NP dynamics, in qualitative contrast with the mechanical response. Hence, the present study has revealed key aspects of the collective motions of NPs connected by polymer bridges in contact with a viscous adsorbing polymer medium and identifies some outstanding remaining challenges for the theoretical understanding of these complex soft materials.