中文摘要：

利用分子动力学模拟方法,针对实验上的超支化分子建立其粗粒化模型,模拟研究了该超支化分子在水和空气的界面上形成Langmuir单分子层的过程,并分析了通过自组装形成的纤维的微观结构.该纤维是由单排超支化分子线性排列形成,超支化分子的末端碳链裸露在空气中,且处于伸展的竖起状态.调节末端支链的亲疏水性能够影响形成的自组装结构,末端支链越亲水,超支化分子越不容易形成一维纳米纤维结构.

英文摘要：

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