Lee Sanghun, Jeong Wonhee, Frank Curtis W, Yoon Do Y
Department of Chemistry, Gachon University, Seongnam, Gyunggido, 13120, Korea.
Cell Development Department, LG Energy Solution, Daejon, 34122, Korea.
Macromol Rapid Commun. 2022 Jun;43(12):e2100614. doi: 10.1002/marc.202100614. Epub 2021 Dec 16.
Molecular dynamics (MD) simulations of melt films of poly(alkyl methacrylate)s (PAMAs) with methyl, ethyl, and n-butyl substituents, respectively, have been performed using an all-atom model to investigate their surface and thin film properties. The applied all-atom force fields predict the bulk densities of PAMAs in good agreement with experiments. Moreover, predictions of the surface tensions of PMMA, PEMA, and Pn-BMA melts are in reasonably good agreement with experiments. The density profiles and orientational-order parameters of chain segments show atomic-scale characteristics in the air/polymer interfacial region. In the surface region, the backbone segments of PAMAs form a well-defined layer structure with the chain vectors oriented parallel to the surface, while the ester side-chains strongly segregate to the surface region and show perpendicular orientation to the surface, with the most pronounced surface segregation noted for Pn-BMA. Such surface segregations of chain segments make it difficult to apply a simple relationship between the cohesive energy density and the surface tension of polymers, for example, and should be taken into account in relating the surface/thin film characteristics to the bulk properties of polymers in general.
分别使用全原子模型对带有甲基、乙基和正丁基取代基的聚甲基丙烯酸烷基酯（PAMA）熔体薄膜进行了分子动力学（MD）模拟，以研究其表面和薄膜性质。所应用的全原子力场预测的PAMA本体密度与实验结果吻合良好。此外，聚甲基丙烯酸甲酯（PMMA）、聚甲基丙烯酸乙酯（PEMA）和聚甲基丙烯酸正丁酯（Pn-BMA）熔体表面张力的预测结果与实验结果也相当吻合。链段的密度分布和取向序参数在空气/聚合物界面区域呈现出原子尺度的特征。在表面区域，PAMA的主链段形成了明确的层状结构，链向量平行于表面取向，而酯侧链强烈偏析到表面区域并呈现垂直于表面的取向，其中Pn-BMA的表面偏析最为明显。例如，链段的这种表面偏析使得聚合物的内聚能密度与表面张力之间难以应用简单的关系，并且在一般情况下将表面/薄膜特性与聚合物的本体性质相关联时应予以考虑。
