Impact of free energy of polymers on polymorphism of polymer-grafted nanoparticles
Impact of free energy of polymers on polymorphism of polymer-grafted nanoparticles
复制标题
聚合物自由能对聚合物接枝纳米粒子多晶型的影响
DOI：
10.1039/d2sm00311b
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发表时间：
2022
期刊：
影响因子：
3.4
通讯作者：
Asai Makoto
中科院分区：
文献类型：
--
作者：
Ishiyama Masanari;Yasuoka Kenji;Asai Makoto
胶体晶体由于其晶体结构和晶格间距控制光的传播的可行性以及其制造的简单性，作为光学应用的模型材料而受到广泛关注。然而，由于胶体之间的相互作用简单，可形成的胶体晶体结构受到限制。调整晶格间距也很困难。此外，与其他晶体相比，胶体晶体是脆弱的。在这项研究中，我们将重点放在聚合物接枝纳米颗粒（PGNP）上，作为这些未解决问题的可能解决方案。我们期望PGNPs由两个不同的层（纳米颗粒的硬核和表面接枝聚合物的软电晕）组成，将表现出与星型聚合物和硬球体相似的行为。我们还预测PGNPs可能表现出多态性，因为PGNPs之间的相互作用强烈依赖于它们的接枝密度和接枝聚合物链的长度。此外，我们预计由PGNPs制成的晶体将由于接枝聚合物的纠缠而具有结构上的韧性。通过分子动力学模拟探索PGNPs的晶体形态，我们发现了面心立方(FCC)/六方紧密堆积（HCP）和体心立方（BCC）晶体，这取决于接枝聚合物链的长度。当链较短时，PGNPs表现为硬球，晶体呈FCC/HCP结构排列，与Alder相变相似。当链足够长时，接枝聚合物的自由能增加不再可以忽略不计，晶体呈BCC结构排列，密度低于FCC/HCP。当链不太短或太长时，当体系体积分数较小时，首先观察到FCC/HCP结构，但当体系进一步压缩，晶体排列成BCC结构时，就会发生相变。这些结果很可能为今后PGNP晶体的模拟和实验研究奠定了坚实的基础。
Colloidal crystals have gathered wide attention as a model material for optical applications because of their feasibility in controlling the propagation of light by their crystal structure and lattice spacing as well as the simplicity of their fabrication. However, due to the simple interaction between colloids, the colloidal crystal structures that can be formed are limited. It is also difficult to adjust the lattice spacing. Furthermore, colloidal crystals are fragile compared to other crystals. In this study, we focused on polymer-grafted nanoparticles (PGNP) as a possible solution to these unresolved issues. We expected that PGNPs, composed of two distinct layers (the hard core of a nanoparticle and the soft corona of grafted polymers on the surface), will demonstrate similar behaviors as star polymers and hard spheres. We also predicted that PGNPs may exhibit polymorphism because the interaction between PGNPs strongly depends upon their grafting density and the length of the grafted polymer chains. Moreover, we expected that crystals made from PGNPs will be structurally tough due to the entanglement of grafted polymers. From exploration of crystal polymorphs of PGNPs by molecular dynamics simulations, we found face-centered cubic (FCC)/hexagonal close-packed (HCP) and body-centered cubic (BCC) crystals, depending on the length of the grafted polymer chains. When the chains were short, PGNPs behaved like hard spheres and crystals were arranged in FCC/HCP structure, much like the phase transition observed in an Alder transition. When the chains were long enough, the increase in the free energy of grafted polymers was no longer negligible and crystals were arranged in BCC structure, which has a lower density than FCC/HCP. When the chains were not too short or long, FCC/HCP structures were first observed when the volume fraction of system was small, but a phase transition occurred when the system was further compressed and the crystals arranged themselves in a BCC structure. These results most likely have laid strong foundations for future simulations and experimental studies of PGNP crystals.