Nanoparticle Loading of Unentangled Polymers Induces Entanglement-Like Relaxation Modes and a Broad Sol-Gel Transition.,The Journal of Physical Chemistry Letters

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Nanoparticle Loading of Unentangled Polymers Induces Entanglement-Like Relaxation Modes and a Broad Sol-Gel Transition.
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2019-08-14 , DOI: 10.1021/acs.jpclett.9b01954
Xue-Zheng Cao _{1,

2} , Holger Merlitz ₃ , M Gregory Forest ₁

Affiliation

We combine molecular dynamics simulations, imaging and data analysis, and the Green-Kubo summation formula for the relaxation modulus G(t) to elicit the structure and rheology of unentangled polymer-nanoparticle composites distinguished by small NPs and strong NP-monomer attraction, εNPM ≫ kBT. A reptation-like plateau emerges in G(t) beyond a terminal relaxation time scale as the volume fraction, cNP, of NPs increases, coincident with a structure transition. A condensed phase of NP-aggregates forms, tightly interlaced with thin sheets of polymer chains, the remaining phase consisting of free chains void of NPs. Rouse mode analyses are applied to the two individual phases, revealing that long-wavelength Rouse modes in the aggregate phase are the source of reptation-like relaxation. Imaging reveals chain motion confined within the thin sheets between NPs and exhibits a 2D analogue of classical reptation. In the NP-free phase, Rouse modes relax indistinguishable from a neat polymer melt. The Fourier transform of G(t) reveals a sol-gel transition across a broad frequency spectrum, tuned by cNP and εNPM above critical thresholds, below which all structure and rheological transitions vanish.

中文翻译：

未缠结的聚合物的纳米粒子负载会导致缠结状的弛豫模式和宽泛的溶胶-凝胶转变。

我们结合分子动力学模拟，成像和数据分析以及Green-Kubo求和公式得出弛豫模量G（t），以得出具有小NP和强NP单体吸引力εNPM的非缠结聚合物-纳米粒子复合材料的结构和流变学。 ≫ kBT。随着NPs的体积分数cNP的增加，在G（t）中出现超过终端松弛时间尺度的类似Ript的平台，这与结构转变相吻合。NP聚集体的凝聚相与聚合物链的薄片紧密交织，剩余的相由不含NP的自由链组成。对两个单独的阶段进行了Rouse模式分析，揭示了聚集相中的长波长Rouse模式是类似repptation的松弛源。成像揭示了链运动限制在NP之间的薄片内，并显示了经典复制的2D类似物。在无NP相中，“唤醒”模式与纯聚合物熔体没有区别。G（t）的傅立叶变换揭示了在宽频谱上的溶胶-凝胶跃迁，通过临界阈值以上的cNP和εNPM进行调谐，在该阈值以下，所有结构和流变跃迁都消失了。

更新日期：2019-08-06

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