The deformation behavior of neat, glassy polymer-grafted nanoparticle (PGN) monolayer films is studied using coarse-grained molecular dynamics simulations and experiments on polystyrene-grafted silica. In both the simulations and experiments, apparent crazing behavior is observed during deformation. The PGN systems show a relatively more uniform, perforated sheet craze structure and significantly higher strain at break than reference homopolymers of the same length. Short chain, unentangled PGN monolayers are also simulated for comparison; these are brittle and break apart without crazing. The entangled PGN simulations are analyzed in detail for systems at both high and moderate graft density. Stress-strain curves show three distinct regions: yielding and strain localization, craze widening, and strain hardening preceding catastrophic failure. The PGN stress-strain behavior appears more similar to that of longer chain, highly entangled homopolymer films than to the reference homopolymer films of the same length as the graft chains, suggesting that the particles effectively add additional entanglement points. The moderate graft density particles have higher strain-to-failure and maximum stress than the high graft density particles. We suggest this increased robustness for lower graft density systems is due to their increased interpenetration of graft chains between neighboring particles, which leads to increased interparticle entanglements per chain.

中文翻译：

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玻璃态聚合物接枝的纳米粒子超薄膜中的单轴变形和裂纹。

使用粗粒度的分子动力学模拟和聚苯乙烯接枝的二氧化硅的实验研究了纯净的玻璃态聚合物接枝的纳米颗粒（PGN）单层膜的变形行为。在模拟和实验中，在变形过程中都观察到明显的开裂行为。与相同长度的参考均聚物相比，PGN系统显示出相对更均匀的穿孔板状裂纹结构，并且断裂时的应变明显更高。还对短链，无缠结的PGN单层进行了仿真，以进行比较。这些都是脆性的，不会破裂而破裂。对于在高和中等移植物密度下的系统，将对纠缠的PGN模拟进行详细分析。应力-应变曲线显示了三个不同的区域：在灾难性破坏之前，屈服和应变局部化，裂纹扩展和应变硬化。PGN应力-应变行为与更长的链，高度缠结的均聚物薄膜相比，与与接枝链长度相同的参考均聚物薄膜更相似，这表明颗粒有效地增加了附加的缠结点。中等的移植物密度颗粒比高的移植物密度颗粒具有更高的应变失效和最大应力。我们认为，对于较低的接枝密度系统，这种增强的鲁棒性是由于它们在相邻颗粒之间增加了嫁接链的互穿程度，从而导致每条链的颗粒间缠结增加。这表明粒子有效地增加了附加的缠结点。中等的移植物密度颗粒比高的移植物密度颗粒具有更高的应变失效和最大应力。我们认为，对于较低的接枝密度系统，这种增强的鲁棒性是由于它们在相邻颗粒之间增加了嫁接链的互穿程度，从而导致每条链的颗粒间缠结增加。这表明粒子有效地增加了附加的缠结点。中等的移植物密度颗粒比高的移植物密度颗粒具有更高的应变失效和最大应力。我们认为，对于较低的接枝密度系统，这种增强的鲁棒性是由于它们在相邻颗粒之间增加了嫁接链的互穿程度，从而导致每条链的颗粒间缠结增加。