论文标题
聚合物的自由能对聚合物接枝纳米颗粒的多态性的影响
Impact of Free Energy of Polymers on Polymorphism of Polymer-Grafted Nanoparticles
论文作者
论文摘要
我们专注于聚合物接枝的纳米颗粒（PGNP）。 PGNP由两个不同的层组成：纳米颗粒的硬核和表面上移植聚合物的软电晕。可以预测，具有这两个不同层的PGNP将具有与星形聚合物和硬球相似的行为。 PGNP之间的相互作用在很大程度上取决于其移植密度和接枝聚合物链的长度N。因此，PGNP可能表现出多态性。此外，可以预期，由于接枝聚合物的纠缠，由PGNP制成的晶体在结构上很难。使用分子动力学模拟探索了PGNP的晶体多晶型物。我们成功地根据移植聚合物链的长度找到了FCC/HCP和BCC晶体。当n很小时，PGNP的行为就像硬球。形成的晶体以FCC/HCP结构排列，就像在Alder转变中观察到的相变。当N足够大时，不再忽略接枝聚合物的自由能的增加。因此，在这些系统中形成的晶体在BCC结构中排列，其密度低于FCC/HCP。当n不是太小或不大时，当PGNP的浓度较低时，就会观察到FCC/HCP结构，但是当随着系统的压缩时，PGNPS的浓度变得更高时发生相变。同样，移植聚合物的自由能增加不再被忽略，晶体将自己放在BCC结构中。同样，可以揭示PGNP晶体的晶格间距可以通过链长轻松而广泛地控制。这些结果应该在许多未来的模拟和PGNP晶体的实验研究中起重要作用。
We focus on polymer-grafted nanoparticles (PGNP). A PGNP is composed of two different layers: the hard core of a nanoparticle and the soft corona of grafted polymers on the surface. It is predicted that PGNPs with these two distinct layers will have similar behaviors as star polymers and hard spheres. The interaction between PGNPs strongly depend upon their grafting density and the length of the grafted polymer chains, N. Thus, PGNP may exhibit polymorphism. Moreover, it is expected that crystals made from PGNPs will be structurally tough due to the entanglement of grafted polymers. The crystal polymorph of PGNP is explored using molecular dynamics simulations. We succeeded in finding FCC/HCP and BCC crystals depending on the length of the grafted polymer chain. When N is small, PGNPs behave like hard spheres. The crystals formed are arranged in FCC/HCP structure, much like the phase transition observed in an Alder transition. When N is large enough, the increase in the free energy of grafted polymers can no longer be neglected. Thus, the crystals formed in these systems are arranged in BCC structure, which has a lower density than FCC/HCP. When N is not too small or large, FCC/HCP structures are observed when the concentration of PGNPs is low, but a phase transition occurs when the concentration of PGNPs becomes higher with the compression of the system. Again, the increase in free energy of grafted polymers can no longer be neglected and the crystals arrange themselves in a BCC structure. Also, it can be revealed that the lattice spacing of PGNP crystals can be controlled easily and widely by the chain length. These results should play an important role in many future simulations and experimental studies of PGNP crystals.
