Assembly of Polymer-Grafted Nanoparticles in Polymer Matrices
Assembly of Polymer-Grafted Nanoparticles in Polymer Matrices
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DOI：
10.1021/acsnano.0c05495
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发表时间：
2020-10-27
期刊：
影响因子：
17.1
通讯作者：
Kumar, Sanat K.
中科院分区：
文献类型：
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作者：
Koh, Clement;Grest, Gary S.;Kumar, Sanat K.
Leibler开创了这样的想法，即长度为P的足够长的基质聚合物将自发地使化学上相同的聚合物层去湿，所述聚合物层包含长度为N的链，密集地末端接枝到平坦表面（“刷”）。这种熵驱动的想法通常用于解释实验，其中发现与聚合物链密集接枝的10-20 nm直径的纳米颗粒（NP）与化学上相同的熔体相分离，P/N大于或接近4。在较低的接枝密度下，这些效应也被认为是支撑接枝纳米颗粒自组装成各种结构的基础。为了探索这幅图的有效性，我们进行了大规模的分子动力学模拟接枝纳米粒子在化学性质相同的聚合物熔体。对于我们考虑的纳米颗粒，在约5 nm的直径范围内，我们发现没有相分离，即使P/N = 10的吸引力的情况下。相反，我们发现的行为，更密切地平行实验时，所有的链单体是同样的吸引力，但排斥的NP。因此，我们的研究结果表明，迄今为止研究的实验情况是由hN的表面活性，这是由化学失配b h无机d有机配体（接枝和自由链是化学相同的）驱动。熵效应，即，平移熵的NP和矩阵，混合的接枝物和矩阵的熵，和链的构象熵出现，从而具有二阶效应，即使在这些模型系统的上下文中。
Leibler pioneered the idea that long enough matrix polymers of length P will spontaneously dewet a chemically identical polymer layer, comprising chains of length N, densely end-grafted to a flat surface ("brush"). This entropically driven idea is routinely used to explain experiments in which 10-20 nm diameter narmparticles (NPs) densely grafted with polymer chains are found to phase separate from chemically identical melts for P/N greater than or similar to 4. At lower grafting densities, these effects are also thought to underpin the selfassembly of grafted NPs into a variety of structures. To explore the validity of this picture, we conducted large-scale molecular dynamics simulations of grafted NPs in a chemically identical polymer melt. For the NPs we consider, in the approximate to 5 nm diameter range, we find no phase separation even for P/N = 10 in the absence of attractions. Instead, we find behavior that more closely parallels experiments when all of the chain monomers are equally attractive to each other but repel the NPs. Our results thus imply that experimental situations investigated to date are dominatedby the surfactancy of hN, which driven by the chemical mismatchb h inorganic d the organic ligands (the graft and free chains are chemically identical). Entropic effects, that is, the translational entropy of the NPs and the matrix, the entropy of mixing of the grafts and the matrix, and the conformational entropy of the chains appear to thus have a second-order effect even in the context of these model systems.