Tan Yongqiang, Resasco Daniel E
School of Chemical, Biological and Materials Engineering, University of Oklahoma, 100 East Boyd Street, Norman, Oklahoma 73019, USA.
J Phys Chem B. 2005 Aug 4;109(30):14454-60. doi: 10.1021/jp052217r.
The dispersibility and bundle defoliation of single-walled carbon nanotubes (SWNTs) of small diameter (<1 nm) have been evaluated on CoMoCAT samples with narrow distribution of diameters. As previously observed by photoluminescence and Raman spectroscopy, the CoMoCAT sample exhibits a uniquely narrow distribution of (n,m) structures that remains unchanged after different dispersion conditions. This narrow distribution allowed us to develop a method for quantifying the dispersability of the samples from their optical absorption spectra in terms of two ratios: the "resonance ratio" and the "normalized width." The former is defined as the quotient of the resonant band area and its nonresonant background. The latter is defined as the ratio of the width of the band at half-height to the peak height on a spectrum that has been normalized at 900 nm, making this an intensive property, rather than varying with the path length. In this study of the CoMoCAT sample, we have used the S22 transition corresponding to the (6,5) nanotube to do these calculations, which is the most abundant species. These two ratios provide a quantitative tool to compare different dispersion parameters (time of sonication, degree of centrifugation, etc.) on the same type of sample. From this comparison, an optimal procedure that maximizes the spectral features was selected; this procedure allowed us to contrast various surfactants at different pH values and concentrations. Several surfactants were as good or even better than the one we have used in previous studies, dodecylbenesulfonic acid sodium salt (NaDDBS). Despite differences in their dispersion abilities, none of the surfactants investigated generated new features in the absorption spectra nor changed the distribution of nanotube types, which confirms that the high selectivity of the CoMoCAT sample is in the original sample rather than caused by selective suspension of specific (n,m) nanotubes.
已在具有窄直径分布的CoMoCAT样品上评估了小直径（<1 nm）单壁碳纳米管（SWNTs）的分散性和成束脱叶情况。如先前通过光致发光和拉曼光谱所观察到的，CoMoCAT样品呈现出独特的窄（n,m）结构分布，在不同分散条件下该分布保持不变。这种窄分布使我们能够开发一种方法，根据两个比率从样品的光吸收光谱来量化其分散性：“共振比率”和“归一化宽度”。前者定义为共振带面积与其非共振背景的商。后者定义为在900 nm处已归一化的光谱上半高宽与峰高的比率，这使其成为一种强度性质，而不是随光程长度变化。在对CoMoCAT样品的这项研究中，我们使用了对应于（6,5）纳米管的S22跃迁来进行这些计算，（6,5）纳米管是最丰富的种类。这两个比率提供了一个定量工具，用于比较同一类型样品上不同的分散参数（超声处理时间、离心程度等）。通过这种比较，选择了使光谱特征最大化的最佳程序；该程序使我们能够对比不同pH值和浓度下的各种表面活性剂。几种表面活性剂与我们先前研究中使用的十二烷基苯磺酸钠（NaDDBS）一样好甚至更好。尽管它们的分散能力存在差异，但所研究的表面活性剂均未在吸收光谱中产生新特征，也未改变纳米管类型的分布，这证实了CoMoCAT样品的高选择性存在于原始样品中，而不是由特定（n,m）纳米管的选择性悬浮引起的。
