天然有机质模型化合物分子结构对碳纳米管分散性的影响

研究了不同分子结构的天然有机物质（NOM）模型化合物单宁酸（TA）、没食子酸（GA）和十二烷基苯磺酸钠（SDBS）对碳纳米管（CNTs）分散性的影响.通过计算得出，TA的临界胶束浓度（CMC）为1.12mmol/L，SDBS的CMC为0.24mmol/L，GA在所测试的浓度范围内没有形成胶束.比较NOM在CNTs表面的吸附过程和CNTs的分散过程，表明空间位阻和胶束包裹是2个促进CNTs分散的主要机理.借助透射电子显微镜（TEM）和测量悬浮的CNTs的平均流体动力学直径（DLS）结果表明，TA在较少的固相吸附量（S_e ≈ 0.01mmol/g）就能使CNTs分散，归因于其吸附后刚性芳香三维结构的TA能形成的较大空间位阻；同样具有芳香平面结构的GA分子在CNTs表面的吸附需要达到一定的厚度（S_e > 0.2mmol/g），才能有效地分散CNTs；具有烷基脂肪链的SDBS，需要在形成半胶束或胶束后（S_e > 0.13mmol/g） CNTs才能有效地被分散.芳香族刚性结构和脂肪族柔性结构的模型化合物对CNTs的分散效果和机理存在较大的差别.

Effect of molecular structure on dispersion of carbon nanotubes by natural organic matter surrogates

In this study, gallic acid (GA), tannic acid (TA) and sodium dodecyl benzene sulfonate (SDBS) were chosen as surrogates of natural organic matter (NOM) to investigate the effects of chemical structures on carbon nanotubes (CNTs) suspension. The critical micelle concentration (CMC) of TA (CMC_TA) was 1.12mmol/L and the CMC_SDBS was 0.24mmol/L. But GA could not form micelles in the range of tested concentration. Comparing the adsorption process of NOM on CNTs and the dispersion process of CNTs, it was showed that steric hindrance and micellar encapsulation were the two main mechanisms for promoting CNTs dispersion. The transmission electron microscopy (TEM) and average hydrodynamic diameter (DLS) of suspended CNTs were measured. Less adsorption (S_e ≈ 0.01mmol/g) for the rigid structure of TA can lead to higher CNT suspension than SDBS with the flexible structure which was hardly dispersed due to the entanglement of alkane chain on CNTs surface. The suspension of CNT was the worst in the plane structure GA (S_e > 0.2mmol/g) due to the poor steric hindrance. The semi-micelles and micelles of SDBS (S_e > 0.13mmol/g) can be formed over CMC. The suspension of CNT can be increased by the micellar wrapping. This study highlighted that the steric hindrance and micellar wrapping were the main dispersion mechanisms of CNTs, depending on different the NOM structures.