Role of Grafting Mechanism on the Polymer Coverage and Self-Assembly of Hairy Nanoparticles
Role of Grafting Mechanism on the Polymer Coverage and Self-Assembly of Hairy Nanoparticles
复制标题
DOI：
10.1021/acsnano.7b02657
复制
发表时间：
2017-07-01
期刊：
影响因子：
17.1
通讯作者：
Kumar, Sanat K.
中科院分区：
文献类型：
--
作者：
Asai, Makoto;Zhao, Dan;Kumar, Sanat K.
现在人们普遍认为，控制纳米颗粒（NP）的空间分散性（可以通过用不同链长和接枝密度的聚合物接枝纳米颗粒来实现）对于优化所得聚合物纳米复合材料的热机械性能至关重要。一般来说，有两种方法来制备这种聚合物接枝纳米粒子：“接枝到”和“接枝自”。传统观点认为，“接枝”机制，即单体尺寸的引发剂/官能团附着到表面，然后生长链，允许更高的聚合物接枝密度，从而使聚合物覆盖纳米颗粒表面更均匀。在这里，我们进行计算，结果表明“接枝”策略令人惊讶地在给定的接枝密度下导致纳米粒子表面的聚合物覆盖更加均匀，因为刷子是在尊重先前接枝链的排除体积限制的情况下形成的。这一结论在低至中等接枝密度的限制下尤其明显。因此，在给定的接枝密度下，“接枝”机制导致纳米颗粒在基质（其化学性质与接枝物相同）中的混溶性增强，并降低产生自组装结构的倾向。另一个重要因素是，在“接枝到”系统的情况下，纳米粒子上的接枝链数量的分散性也较小，从而产生更好的材料。这两个结论意味着“接枝”机制可以更好地控制纳米颗粒分散状态，从而更好地控制聚合物纳米复合材料的热机械性能。
It is now well-accepted that controlling the spatial dispersion of nanoparticles (NPs), which can be achieved by grafting them with polymers of different chain lengths and grafting densities, is central to optimizing the thermomechanical properties of the resulting polymer nanocomposites. In general, there are two methods for creating such polymer-grafted NPs: "grafting to" and "grafting from". The conventional wisdom is that the "grafting from" mechanism, where monomer-sized initiator/functional groups are attached to the surface followed by growing the chains, allows for higher polymer grafting densities and hence a more uniform polymer coverage of the NP surface. Here, we perform calculations and instead show that the "grafting to" strategy surprisingly leads to a more uniform polymer coverage of the NP surface at a given grafting density since the brush is formed while respecting the excluded volume constraints of the previously grafted chains This conclusion is especially clear in the limit of low-to moderate grafting density. Thus, at a given grafting density, the "grafting to" mechanism leads to an enhanced miscibility of the NPs in the matrix (which has the same chemistry as the grafts) and lower propensity to create self-assembled structures. Another important factor is that the dispersity in the number of grafted chains on the NPs is also smaller in the case of "grafting to" systems, thus leading to better defined materials. These two conclusions imply that the "grafting to" mechanism may provide better control over the NP dispersion state and hence the thermomechanical properties of polymer nano composites.