Kyrychenko Alexander, Pasko Dmitry A, Kalugin Oleg N
Institute of Chemistry, V. N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv 61022, Ukraine.
School of Chemistry, V. N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv 61022, Ukraine.
Phys Chem Chem Phys. 2017 Mar 29;19(13):8742-8756. doi: 10.1039/c6cp05562a.
Chemical modification of silver nanoparticles (AgNPs) with a stabilizing agent, such as poly(vinyl alcohol) (PVA), plays an important role in shape-controlled seeded-growth and colloidal stability. However, theoretical aspects of the stabilizing mechanism of PVA are still poorly understood. To gain a better understanding of the role of PVA in water protecting effects for silver nanoparticles, we developed an atomistic model of a AgNP grafted with single-chain PVA of various lengths. Our model, designed for classical molecular dynamics (MD) simulations, approximates the AgNP as a quasi-spherical silver nanocrystal with 3.9 nm diameter and uses a united-atom representation for PVA with its polymer chain length varying from 220 up to 1540 repeating units. We found that PVA adsorbs onto the AgNP surface through multiple non-covalent interactions, among which non-covalent bonding of the hydroxyl groups plays a key role. The analysis of adsorption isotherms by using the Hill, Scatchard, and McGhee & von Hippel models exhibits evidence for positive binding cooperativity with the cooperativity parameter varying from 1.55 to 2.12. Our results indicate that the size of the PVA polymer rather than its structure plays a crucial role in providing water protecting effects for the AgNP core, varying from 40% up to 91%. The water-protecting efficiency was well approximated by the Langmuir-Freundlich equation, allowing us to predict that the saturated coverage of the nanoparticle of a given diameter of 3.9 nm should occur when the PVA molecular weight approaches 115 kDa, which corresponds to the number of vinyl alcohol monomers being equal to 3100 units.
用稳定剂（如聚乙烯醇（PVA））对银纳米颗粒（AgNP）进行化学修饰，在形状可控的种子生长和胶体稳定性方面起着重要作用。然而，PVA稳定机制的理论方面仍知之甚少。为了更好地理解PVA在银纳米颗粒水保护作用中的作用，我们构建了一个接枝有不同长度单链PVA的AgNP原子模型。我们的模型专为经典分子动力学（MD）模拟设计，将AgNP近似为直径3.9 nm的准球形银纳米晶体，并对PVA采用联合原子表示法，其聚合物链长度从220个重复单元到1540个重复单元不等。我们发现PVA通过多种非共价相互作用吸附在AgNP表面，其中羟基的非共价键起着关键作用。使用希尔、斯卡查德和麦吉&冯·希佩尔模型对吸附等温线的分析表明存在正结合协同性，协同性参数在1.55至2.12之间变化。我们的结果表明，PVA聚合物的大小而非其结构在为AgNP核心提供水保护作用方面起着关键作用，水保护效率从40%到91%不等。水保护效率可以很好地用朗缪尔-弗伦德利希方程近似，这使我们能够预测，当PVA分子量接近115 kDa（对应于乙烯醇单体数量等于3100个单元）时，直径为3.9 nm的给定纳米颗粒应达到饱和覆盖。
