Abstract:

Based on the Martini force field, the structure of Pluronic block copolymer on the hydrophobic nano-surface self-assembled film was studied by coarse-grained molecular dynamics simulation. The effect of structure of Pluronic copolymer on the self-assembled monolayer film structure is studied systematically. As simulation results show the core-shell structure of polymer-nanoparticle composites were formed whose core originates from nanoparticle while their shell is composed with Pluronic copolymer. The concentration and structure of Pluronic copolymers have a significant influence on the core-shell structure. At lower concentration, a completely covered film was observed with crimp configuration of ethylene oxide (EO) blocks, meanwhile layered film covered on the NP surface. With further rise in the concentration, star-shaped films with stretching configuration of EO blocks were formed. The thickness of shell-layer increases as increasing the relative molecular weights of polymers. Moreover, Pluronic copolymers revealed a special assembled pattern on a NP surface: transform from “S-shaped” to “W-shaped” or “U-shaped” as increasing the molar ratio of propylene oxide (PO). This result may be caused by the fact that limited hydrophobic NP surface can t provide enough adsorption sites as increasing the polymer concentration.

Key words: core-shell structure, polymer, nanoparticle composites, coarse-graining, molecular simulations, self-assembled film

摘要：

基于Martini力场采用粗粒化分子动力学模拟研究了Pluronic嵌段共聚合物在疏水纳米表面自组装膜结构，考察了Pluronic嵌段共聚合物结构对自组装单分子膜结构的影响。模拟结果发现Pluronic聚合物在疏水纳米表面自组装形成了以纳米材料为核，聚合物为壳的特殊核-壳结构。聚合物的浓度和结构都会影响该壳层结构，在浓度较低时，聚合物EO嵌段卷曲地附着在疏水纳米颗粒表面，类似形成层状的壳层结构；随着浓度的提高，EO嵌段伸向溶剂相，形成星形自组装膜结构。增加Pluronic共聚物相对分子质量，吸附在纳米材料的聚合物壳层厚度也逐渐增加。随着聚合物PO摩尔的增加，吸附在纳米材料表面的PO嵌段由“S”形或“W”形吸附逐渐变成“U”形吸附。这可能因为随着聚合物浓度的提高，有限的纳米颗粒表面不足以提供足够多的吸附位点导致聚合物吸附构型转变。

关键词: 核-壳结构, 聚合物, 纳米复合材料, 粗粒化, 分子模拟, 自组装膜