Computer simulation study on the formation of nanofibers by hyper branched molecules
writer：Y.-L. Zhu, Z.-W. Li, Z.-Y. Sun, Z.-Y. Lu
keywords：Hyper branched molecules
source：期刊
specific source：Acta Polymerica Sinica, 2017
Issue time：2017年
Long-range and one-dimensional nanofibers assembled by hyper branched molecules were observed in experiments. Intuitively, the isotropic hyper branched molecules are not expected to form regularly one-dimensional self-assembly structures. The formation mechanism and detailed structures of the self-assembly nanofibers are still unclear. In this work, we employed molecular dynamics simulation to study the formation process of these one-dimensional nanofibers. We built the coarse-grained model of the hyper branched molecules reported in experiments, and studied the formation of Langmuir condensed monolayer by gradually decreasing the surface area of air-water interface, where the hyper branched molecules were adsorbed. The detailed structures of the self-assembled nanofibers were identified in simulation, which can help to understand experimental results from a microscopic point of view. To be specific, we observed the one-dimensional nanofibers which consist of only one row of molecules, different from the speculation in experiments that the nanofibers may consist of multi-rows of molecules. We also found that the hydrophobic alkyl tails were oriented upwards to the air, covering most part of the core region of the hyper branched molecules, in agreement with the experiments. The influence of the interactions between terminal branches on the self-assembled structures was also studied. With strong attractions between terminal branches, large sheets of aggregation structure were formed by the hyper branched molecules. While with weak attractions, short linear micelles were formed. The one-dimensional nanofibers were formed only when the attractions between terminal branches were in a range of moderate intensity. In addition, we studied also the influence of the interactions between terminal branches and water on the formation of the nanofiber structure. It was found that suitable hydrophobicity was crucial for the formation of the nanofiber structure, and the hydrophilic terminal branches hindered the formation of the one-dimensional nanofibers. Instead, short linear micelles will be formed between the hyper branched molecules and the hydrophilic terminal branches.