Aragon Institute of Technology ITAINNOVA, María de Luna 7-8, Zaragoza 50018, Spain.
Aragon Institute of Engineering Research (I3A), University of Zaragoza, Zaragoza 50018, Spain.
Soft Matter. 2022 Apr 6;18(14):2800-2813. doi: 10.1039/d1sm01794b.
Polymer/silica (PS) nanocomposites are, among numerous combinations of inorganic/organic nanocomposites, one of the most important materials reported in the literature and have been employed in a wide variety of applications. Due to this great interest in the scientific and industry community, knowledge about their physiochemistry allows for a better understanding of their development and improvement. One area of interest found in biopolymers is silica, where silica nanoparticles can be used to increase their mechanical properties and give them higher opportunities to replace synthetic plastics. With this aim in mind, molecular dynamics (MD) simulations were used to predict the structure and mechanical properties of the interphase region and nanocomposite systems of polycaprolactone (PCL), a common poly(hydroxy acid) type biopolymer, reinforced with silica nanoparticles. Two types of nanoparticles were studied to assess the effect of PEGylation: hydroxyl (ungrafted) and polyethylene glycol (PEG) (grafted or PEGylated) functionalized silica. The interaction energy between the nanoparticle and the polymeric matrix was determined, showing an increase of the affinity between each component due to the PEGylation of the nanoparticle. Through the analysis of polymer density profiles, the structure and thickness of the interphase region were determined, and it was observed that PEGylation increased the interphase thickness from 10.80 Å to 13.04 Å while it decreased the peak and average polymer density of the interphase region. Using compressed and expanded molecular models of the neat PCL polymer, the mechanical properties of the interphase region were related to its density through an interpolation model, and mechanical property profiles were obtained, from which the average values of the Young's modulus, Poisson's ratio and shear modulus of the interphase region were calculated. Finally, the mechanical properties of the nanocomposites were determined by molecular mechanics simulations, showing that the silica nanoparticles increased the stiffness of the composite system to about 7-8% with respect to that of the neat polymer, having a 2.09% weight of bare silica or 2.82% weight of PEGylated silica. PEGylation did not show an additional effect on the overall mechanical properties. A mean field micromechanics model (Mori-Tanaka) corroborated the properties calculated for the interphase region using MD simulations. It was concluded that the PEGylation of the nanoparticle improved the affinity, and thus the dispersion, of the silica nanoparticles towards the PCL matrix, but with no further increase in the mechanical properties of the composite.
聚合物/二氧化硅（PS）纳米复合材料是无机/有机纳米复合材料众多组合中的一种，是文献中报道的最重要的材料之一，并已广泛应用于各种应用中。由于科学界和工业界对此非常感兴趣，因此对其物理化学性质的了解有助于更好地理解其发展和改进。在生物聚合物中，人们对二氧化硅感兴趣的一个领域是，二氧化硅纳米颗粒可用于提高其机械性能，并为其提供更多替代合成塑料的机会。考虑到这一目标，使用分子动力学（MD）模拟来预测聚己内酯（PCL）的界面区域和纳米复合材料系统的结构和力学性能，PCL 是一种常见的多羟基酸型生物聚合物，用二氧化硅纳米颗粒增强。研究了两种类型的纳米颗粒来评估 PEG 化的效果：羟基（未接枝）和聚乙烯醇（PEG）（接枝或 PEG 化）功能化的二氧化硅。确定了纳米颗粒与聚合物基体之间的相互作用能，表明由于纳米颗粒的 PEG 化，各组分之间的亲和力增加。通过分析聚合物密度分布，确定了界面区域的结构和厚度，并观察到 PEG 化使界面厚度从 10.80 Å 增加到 13.04 Å，同时降低了界面区域的峰值和平均聚合物密度。通过使用纯 PCL 聚合物的压缩和扩展分子模型，通过插值模型将界面区域的力学性能与其密度相关联，并获得力学性能曲线，从中计算出界面区域的杨氏模量、泊松比和剪切模量的平均值。最后，通过分子力学模拟确定了纳米复合材料的力学性能，结果表明，与纯聚合物相比，二氧化硅纳米颗粒使复合材料系统的刚度增加了约 7-8%，纯二氧化硅的重量为 2.09%，或接枝的二氧化硅的重量为 2.82%。PEG 化对整体力学性能没有显示出额外的影响。平均场细观力学模型（Mori-Tanaka）证实了使用 MD 模拟计算的界面区域的性质。结论是，纳米颗粒的 PEG 化提高了纳米颗粒对 PCL 基体的亲和力，从而提高了其分散性，但复合材料的力学性能没有进一步提高。
