SDS Surfactants on Carbon Nanotubes: Aggregate Morphology
SDS Surfactants on Carbon Nanotubes: Aggregate Morphology
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DOI：
10.1021/nn8007756
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发表时间：
2009-03-01
期刊：
影响因子：
17.1
通讯作者：
Striolo, Alberto
中科院分区：
文献类型：
--
作者：
Tummala, Naga Rajesh;Striolo, Alberto
虽然碳纳米管已经吸引了巨大的研究兴趣，但它们的实际应用仍然受到阻碍，主要是由于难以将它们分离成直径，手性和长度单分散的样品。最近的进展表明，表面活性剂稳定的碳纳米管分散体的超离心是一种有前途的途径，实现所需的分离。为了进一步完善这一过程，有必要知道表面活性剂如何吸附在不同直径的纳米管上，这决定了纳米管-表面活性剂聚集体的有效密度和平均力的纳米管-纳米管势。由于只有有限的实验数据可用于阐明这些现象，我们在这里报告了广泛的全原子分子动力学研究十二烷基硫酸钠（SDS）表面活性剂聚集体的形态吸附在（6，6），（12，12），（20，20）单壁碳纳米管在室温条件下。我们的计算表明，纳米管直径是决定聚集体形态的主要因素，因为表面活性剂在包裹一个纳米管时遇到的熵和能量优势之间的竞争，以及在此过程中由于表面活性剂分子的弯曲而面临的摩擦惩罚。这些数据与Yurekli等人[J. Am. 2004，126，9902]，并且首次提供了有助于设计更好的分离的原子级描述，以及用于水性碳纳米管分散体的稳定化技术。
Although carbon nanotubes have attracted enormous research interest, their practical application is still hindered, primarily, by the difficulty of separating them into samples monodispersed in diameter, chirality, and length. Recent advances show that ultracentrifugating carbon nanotube dispersions stabilized by surfactants is a promising route for achieving the desired separation. For further perfectioning this procedure it is necessary to know how surfactants adsorb on nanotubes of different diameters, which determines the nanotube-surfactant aggregate effective density and the nanotube-nanotube potential of mean force. Because only limited experimental data are available to elucidate these phenomena, we report here an extensive all-atom molecular dynamics study on the morphology of sodium dodecyl sulfate (SDS) surfactant aggregates adsorbed on (6,6), (12,12), and (20,20) single walled carbon nanotubes at room conditions. Our calculations reveal that the nanotube diameter is the primary factor that determines the morphology of the aggregates because of a competition between the entropic and energetic advantage encountered by the surfactants when they wrap one nanotube, and the enthalpic penalty faced during this process due to bending of the surfactant molecule. The data are in qualitative agreement with the neutron scattering results reported by Yurekli et al. [J. Am. Chem. Soc. 2004, 126, 9902], and for the first time provide an atomic-level description helpful in designing better separation, as well as stabilization techniques for aqueous carbon nanotube dispersions.