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首页> 外文期刊>The Journal of Chemical Physics >Adsorption and diffusion of colloidal Au nanoparticles at a liquid-vapor interface
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Adsorption and diffusion of colloidal Au nanoparticles at a liquid-vapor interface

机译：胶体金纳米颗粒在液-汽界面的吸附和扩散

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Motivated by recent drop-drying experiments of Au nanoparticle (NP) island self-assembly, we investigate the structure, diffusion, and binding of dodecanethiol-coated Au NPs adsorbed at the toluene-vapor interface using molecular dynamics (MD) simulations as well as analytical calculations. For a 6 nm core diameter NP our results indicate the existence of significant intermixing between the ligands and the solvent. As a result, the NP lies primarily below the interface with only a portion of the ligands sticking out, while the toluene-vapor interface is significantly higher in the region above the NP core than away from the NP. These results are consistent with a competition between the negative free energy of mixing of toluene and the dodecanethiol ligands, which tends to keep the NP below the interface, and the effects of surface tension which keeps the NP near the interface. Consistent with this result, we find that the coefficient for nanoparticle diffusion along the interface is close to the Stokes-Einstein prediction for three-dimensional bulk diffusion. An analysis of the ligand arrangement surrounding the NP also indicates that there is relatively little asymmetry in the ligand-coating. We then consider the effects of van der Waals interactions on the adsorption energy. In particular, we derive an analytical expression for the van der Waals interaction energy between a coated nanoparticle and the surrounding solvent along with a closed-form expression for the van der Waals corrections to the binding energy at the interface due to the long-range core-solvent interaction. Using these results along with the results of our MD simulations, we then estimate the van der Waals corrections to the adsorption energy for dodecanethiol-coated Au nanoparticles at the toluene-vapor interface as well as for decanethiol-coated nanoparticles at the water-vapor interface. In both cases, we find that the long-range core-solvent interaction may significantly reduce the binding energy. Based on these results, we conclude that in many cases, the core-solvent van der Waals interaction is likely to have a significant effect on the binding energy and interface position of Au NPs. Our results also indicate that the competition between the van der Waals interaction and the short-range attraction to the interface leads to the existence of well-defined activation barriers for nanoparticle adsorption from the solvent as well as for interfacial desorption.
机译：根据最近的金纳米粒子（NP）岛自组装的液滴干燥实验的动机，我们使用分子动力学（MD）模拟以及吸附在甲苯-蒸汽界面的十二烷硫醇包覆的金纳米颗粒的结构，扩散和结合分析计算。对于6 nm核心直径NP，我们的结果表明，配体和溶剂之间存在明显的混合。结果，NP主要位于界面下方，只有一部分配体伸出，而甲苯-蒸气界面在NP核心上方的区域中明显高于远离NP的区域。这些结果与甲苯和十二烷硫醇配体混合的负自由能之间的竞争相一致，后者倾向于使NP保持在界面以下，而表面张力的影响则使NP保持在界面附近。与此结果一致，我们发现纳米粒子沿界面扩散的系数接近于三维本体扩散的斯托克斯-爱因斯坦预测。对围绕NP的配体排列的分析还表明，配体涂层中的不对称性相对较小。然后，我们考虑范德华相互作用对吸附能的影响。特别是，我们推导了涂层纳米粒子与周围溶剂之间范德华相互作用能的解析表达式，以及由于长程核对界面处的结合能进行范德华校正的封闭式表达式-溶剂相互作用。利用这些结果以及我们的MD模拟结果，我们可以估算对甲苯-蒸汽界面处十二烷硫醇包覆的Au纳米粒子以及水-蒸汽界面处癸硫醇包覆的纳米粒子的吸附能进行范德华校正。在这两种情况下，我们发现核溶剂之间的长距离相互作用可能会大大降低结合能。根据这些结果，我们得出结论，在许多情况下，核-溶剂范德华相互作用可能对Au纳米粒子的结合能和界面位置产生重大影响。我们的研究结果还表明，范德华相互作用和对界面的短程吸引之间的竞争导致存在明确定义的活化壁垒，该壁垒对于从溶剂中吸附纳米粒子以及界面解吸而言都是存在的。

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