Deformation Behavior of Polystyrene-Grafted Nanoparticle Assemblies with Low Grafting Density
Deformation Behavior of Polystyrene-Grafted Nanoparticle Assemblies with Low Grafting Density
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DOI：
10.1021/acs.macromol.8b01524
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发表时间：
2018-09-25
期刊：
影响因子：
5.5
通讯作者：
Vaia, Richard A.
中科院分区：
文献类型：
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作者：
Jiao, Yang;Tibbits, Andrew;Vaia, Richard A.
无基质、聚合物接枝的纳米颗粒（PGN）组件显示出广泛的结构、光子和电气应用前景。我们研究了低接枝密度（Sigma < 0.15链/nm(2)）下聚苯乙烯接枝Fe3O4 （Fe3O4- ps）组件的模量、屈服强度和裂纹。从起皱-开裂方法（WCM）中，我们发现模量(E)和屈服应力（sigma(y)）与纳米级薄膜厚度（70 < h(f) < 250 nm）和接枝分子量（30 kDa < MW < 370 kDa）无关，并且与有效介质理论的预测非常吻合。此外，TEM的薄膜开裂观察表明，无基体PGN组件的最大变形能力有两个临界长度尺度：(1)PGN核心尺寸应小于开裂微观结构的临界长度尺度；(2)邻近缠结优化为最低接枝长度(N)，其中PGN结构具有中等接枝密度(r（0)Sigma（0.5）近似于3-6，N/N-e近似于4-6）。这些发现为优化设计提供了基础，同时最大化了PGN薄膜组件的无机体积分数、可加工性和机械稳健性。
Matrix-free, polymer-grafted nanoparticle (PGN) assemblies show promise for a wide array of structural, photonic, and electrical applications. We examine the modulus, yield strength, and crazing of assemblies of polystyrene grafted Fe3O4 (Fe3O4-PS) at low graft density (Sigma < 0.15 chains/nm(2)) where chain entanglements are maximized. From the wrinkling-cracking method (WCM) we show that modulus (E) and yield stress (sigma(y) ) are independent of nanoscale film thickness (70 < h(f) < 250 nm) and graft molecular weight (30 kDa < MW < 370 kDa) and in good agreement with predictions from effective medium theory. Furthermore, thin film craze observations from TEM imply two critical length scales for maximum deformability of matrix-free PGN assemblies: (1) PGN core size should be less than the critical length scale of the craze microstructure, and (2) near-neighbor entanglements are optimized for the lowest graft length (N) where the PGN architecture exhibit intermediate graft densities (r(0)Sigma(0.5) similar to 3-6 and N/N-e similar to 4-6). These findings provide a foundation for optimizing designs that simultaneously maximize inorganic volume fraction, processability, and mechanical robustness for PGN thin film assemblies.