Department of Mathematics and Applied Mathematics, University of Crete, Heraklion70013, Greece.
Institute of Applied and Computational Mathematics, Foundation for Research and Technology-Hellas, Heraklion70013, Greece.
J Phys Chem B. 2022 Oct 6;126(39):7745-7760. doi: 10.1021/acs.jpcb.2c04325. Epub 2022 Sep 22.
The dynamics of polymer chains in poly(ethylene oxide)/silica (PEO/SiO) nanoparticle nanohybrids have been investigated via a combined computational and experimental approach involving atomistic molecular dynamics simulations and dielectric relaxation spectroscopy (DRS) measurements. The complementarity of the approaches allows us to study systems with different polymer molecular weights, nanoparticle radii, and compositions across a broad range of temperatures. We study the effects of spatial confinement, which is induced by the nanoparticles, and chain adsorption on the polymer's structure and dynamics. The investigation of the static properties of the nanocomposites via detailed atomistic simulations revealed a heterogeneous polymer density layer at the vicinity of the PEO/SiO interface that exhibited an intense maximum close to the inorganic surface, whereas the bulk density was reached for distances ∼1-1.2 nm away from the nanoparticle. For small volume fractions of nanoparticles, the polymer dynamics, probed by the atomistic simulations of low-molecular-weight chains at high temperatures, are consistent with the presence of a thin adsorbed layer that exhibits slow dynamics, with the dynamics far away from the nanoparticle being similar to those in the bulk. However, for high volume fractions of nanoparticles (strong confinement), the dynamics of all polymer chains were predicted slower than that in the bulk. On the other hand, similar dynamics were found experimentally for both the local β-process and the segmental dynamics for high-molecular-weight systems measured at temperatures below the melting temperature of the polymer, which were probed by DRS. These differences can be attributed to various parameters, including systems of different molecular weights and nanoparticle states of dispersion, the different temperature range studied by the different methods, the potential presence of a reduced-mobility PEO/SiO interfacial layer that does not contribute to the dielectric spectrum, and the presence of amorphous-crystalline interfaces in the experimental samples that may lead to a different dynamical behaviors of the PEO chains.
通过原子分子动力学模拟和介电弛豫光谱（DRS）测量相结合的计算和实验方法，研究了聚环氧乙烷/二氧化硅（PEO/SiO）纳米粒子纳米杂化物中聚合物链的动力学。这些方法的互补性使我们能够研究具有不同聚合物分子量、纳米粒子半径和组成的系统，温度范围广泛。我们研究了空间限制（由纳米粒子引起）和链吸附对聚合物结构和动力学的影响。通过详细的原子模拟研究纳米复合材料的静态特性，发现靠近 PEO/SiO 界面处的聚合物密度呈现不均匀分布，在无机表面附近存在强烈的最大值，而在距纳米粒子约 1-1.2nm 处则达到了体相密度。对于纳米粒子的小体积分数，通过在高温下对低分子量链的原子模拟研究聚合物动力学，发现存在一个薄的吸附层，其动力学较慢，远离纳米粒子的动力学与体相中的动力学相似。然而，对于纳米粒子的高体积分数（强限制），所有聚合物链的动力学都被预测比体相中的动力学慢。另一方面，通过 DRS 测量，在低于聚合物熔点的温度下，对于高分子量系统的局部β过程和链段动力学，实验上也发现了类似的动力学。这些差异可以归因于各种参数，包括不同分子量的系统和纳米粒子分散状态、不同方法研究的不同温度范围、可能存在的对介电谱没有贡献的低迁移率 PEO/SiO 界面层，以及实验样品中无定形-结晶界面的存在，这可能导致 PEO 链的不同动力学行为。
