Simulation of CTAB bilayer adsorbed on Au(100), Au(110), and Au(111) surfaces: structure stability and dynamic properties
Received date: 2016-04-13
Revised date: 2016-05-12
Online published: 2017-01-15
Supported by
Supported by the National Basic Research Program (2012CB932504)
金纳米棒的各向异性生长常被认为是由于金表面吸附溴化十六烷基三甲基铵（CTAB）双分子层导致的。利用密度泛函理论（DFT）研究溴离子在（100）、（110）和（111）3种金表面上可能的吸附位点，根据它构建金表面CTAB双分子层模型，再利用分子动力学模拟方法研究这种烷基链互相交错排布的双分子层的结构。此外，动力学性质研究表明外层CTAB有着明显的横向扩散现象，而在法向上则出现上下起伏振动。相比较而言，在（111）表面上的双分子层结构的横向扩散和法向涨落更加显著。用外层单个CTA+脱离双分子层所需要的能量表征金表面CTAB双分子层的稳定性。结果表明（111）表面的CTAB双分子层的稳定性弱于其他两种金表面上的CTAB双分子层。认为这是因为（111）表面上的CTAB双分子层的排布密度相对较低，导致它相对于其他两种表面的双分子层有更高的扩散性和较低的稳定性。这可能是金纳米颗粒倾向于沿（111）表面生长的原因。
潘俊 , 胡中波 . 吸附在Au(100)、Au(110)和Au(111)表面的CTAB双分子层的结构和动力学性质的分子模拟[J]. 中国科学院大学学报, 2017 , 34(1) : 38 -49 . DOI: 10.7523/j.issn.2095-6134.2017.01.006
Anisotropic growth of gold nanorods is often attributed to the adsorption of surfactant cetyltrimethyl ammonium bromide (CTAB) bilayer on gold facets. In this work, we performed DFT (density function theory) calculations to investigate possible binding sites of Br ions on Au(100), Au(110), and Au(111) facets. The CTAB bilayers on these facets were then constructed, and the structures of these interdigitated bilayers were studied by using molecular dynamics simulation. In addition, the dynamic properties of CTAB bilayer were investigated, and the results indicate that the outer layer exhibits noticeable lateral diffusion and undergoes fluctuation along surface normal. Both lateral diffusion and surface normal fluctuation of CTAB bilayer on Au(111) facet are more profound. The stability of CTAB bilayers on gold surfaces was estimated in terms of the required energy for dissociation of a CTA+ ion from the outer layer. The stability of CTAB bilayer on Au(111) is considerably weaker than on Au(100) and Au(110). Higher volatility and weaker stability may be due to lower packing density of CTAB bilayer on Au(111) facet, and both of them induce the growth tendency of gold nanoparticles along the (111) direction.
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