两亲分子对碳纳米管的分散稳定作用

综述了近年来国内外对碳纳米管在两亲分子水溶液中的分散作用研究, 从表面活性剂、聚合物和生物大分子三方面, 分别阐述了用非成键法对碳纳米管进行分散的不同机理. 离子型表面活性剂或聚电解质主要靠亲水基团之间的静电斥力阻止碳纳米管之间的聚集, 而非离子型表面活性剂或大分子则主要靠亲水基团所产生的空间位阻使分散体系保持稳定.     

高稳定性和水溶性的共轭聚电解质/单壁碳纳米管复合物的制备和表征

单壁碳纳米管（SWNTs）的分散性是影响其走向大规模应用的一个重要因素.尤其为满足未来绿色化学的要求,制备环保、稳定、均匀分散的单壁碳纳米管水溶液尤为重要.基于此,我们利用一种水溶性的共轭聚电解质聚（3-甲基咪唑盐己基噻吩）（P3MHT）,来分散单壁碳纳米管.通过紫外-可见光谱仪、荧光光谱仪、透射电子显微镜、纳米粒度-Zeta电位分析仪、热重分析仪等仪器对制备的聚噻吩/碳纳米管复合物进行表征,结果表明聚噻吩主链与碳纳米管通过π-π相互作用形成电荷转移复合物,聚噻吩侧链上的离子基团则赋予复合物良好的水溶性,从而均匀分散碳纳米管.与常用于分散碳纳米管的小分子表面活性剂十二烷基硫酸钠相比,相同质量的P3MHT可明显提高碳纳米管在水相中的溶度和均匀分散性.该复合物溶液具有非常高的稳定性,在静置6个月后复合物分散性基本保持不变.     

碳纳米管分散研究进展

碳纳米管由于其独特的结构和性质受到了人们广泛的关注。但是目前制备的碳纳米管经常呈现团聚状态,这样就破坏了单根碳纳米管所具有的优异性能,严重影响了碳纳米管的应用。如何使碳纳米管能够有效地分散成为现在急需解决的问题。影响碳纳米管分散的因素有很多,本文主要综述了表面活性剂、超声振荡和离心这三个方面对碳纳米管分散的影响。     

表面活性剂HLB值与渣油乳化体系分散性及电学性质的关系研究

为了研究表面活性剂亲水亲油平衡值（HLB值）与渣油乳化体系分散性和电学性质的关系,采用粒径和粒径分布相结合的方法来评价乳化体系的分散性,利用电导率值的变化来反应体系电学性质的差异,以表面活性剂B和A复合成实验用渣油乳化分散剂来分散渣油加氢裂化水溶性盐,考察了表面活性剂HLB值对渣油包盐水体系的分散性和电学性质的影响。结果表明,随表面活性剂HLB值从小到大的变化,不同水溶性盐在同种油中的分散性和电学性质不同,同种盐在不同油中的变化也存在着差异。乳化体系的分散性及电学性质随着HLB值的增加呈非线性变化。     

非离子表面活性剂对多壁碳纳米管在乙醇中高浓度分散的作用

如果能在无需聚合物或共价官能团辅助的条件下, 将多壁碳纳米管(MWNTs)高浓度地分散在乙醇中, 那么向各种复合材料引入MWNTs的过程就会更加便捷. 为此, 制备了多种含有表面活性剂的多壁碳纳米管乙醇悬浮液并对比考查了它们的稳定性. 非离子表面活性剂Triton X-100 和Tween 65显示出了在乙醇中分散悬浮高浓度MWNTs的能力, 能够使1.0 g·L-1 MWNTs乙醇悬浮液的上层清液经240 h后浓度仍分别在0.50和0.35 g·L-1以上. 这样长时间稳定的、没有聚合物或共价官能团辅助的MWNTs乙醇悬浮液, 其浓度比文献报道的值高. 进一步探讨了这些非离子表面活性剂分子结构对于分散MWNTs的优势, 并直观给出了其吸附于碳纳米管表面的可能形式. X射线光电子能谱和透射电子显微镜的表征结果都证实了表面活性剂分子吸附于碳纳米管表面.     

表面活性剂对碳纳米管分散性及其湿法纺丝纤维性能的影响

碳纳米管(CNT)纤维因具有低密度、高强度以及高电导率等特性受到广泛关注。在湿法纺丝技术制备CNT纤维的工艺中，探究纺丝分散液和纺丝条件对CNT纤维性能的影响具有重要意义。本文研究了十二烷基硫酸钠(SDS)、十六烷基三甲基溴化铵(CTAB)、胆酸钠(SC)、牛磺脱氧胆酸钠(STDC)等表面活性剂对CNT纤维制备及性能的影响。通过拉曼光谱、紫外可见光谱、偏光显微镜、旋转流变仪、扫描电镜等方法对材料进行表征，以拉伸测试和“四探针”法对材料性能进行测试。结果表明，单壁碳纳米管(SWNTs)在表面活性剂的2(wt)%水溶液中的分散能力顺序依次为STDC> SC> CTAB> SDS;SDS或CTAB修饰的SWNTs分散液无法纺制纤维，SC和STDC修饰的SWNTs分散液具有良好的可纺性。其中以STDC作表面活性剂制备的CNT纤维性能最好，其断裂强度为160MPa,杨氏模量为12.3GPa,电导率为2300S/cm。     

碳纳米管的表面修饰及TiO2-CNTs复合催化剂的光催化性能

运用酸氧化和聚乙烯醇表面修饰碳纳米管, 修饰的碳纳米管的水分散性能显著改善. 进一步地运用低温水热法合成表面修饰的碳纳米管复合TiO₂, 观察到了复合催化剂紫外及可见光激发下的光催化性能的明显提升. 红外光谱、X光电子能谱、差热-热重分析、X光衍射、Brunauer-Emmett-Teller低温氮吸附、透射电镜及紫外-可见漫反射光谱等表征表明, 复合催化剂光催化性能改善与碳纳米管良好水溶液分散性能导致的TiO₂在修饰的碳纳米管表面的均匀、致密分散和密切键合, 从而充分利用碳纳米管的功能密切关联.     

聚乙烯基吡咯烷酮修饰多壁碳纳米管的研究

采用超声波辅助技术,研究了两亲性聚合物聚乙烯基吡咯烷酮(PVP)修饰多壁碳纳米管(MWNTs)的效果、作用机理及影响因素.研究结果表明在适合的条件下两亲性聚合物PVP可以被引入到多壁碳纳米管表面,修饰后的MWNTs在DMF、乙醇和水等溶剂中具有良好的分散性.通过红外光谱(FTIR)和拉曼光谱(Raman)分析表明,两亲性聚合物与MWNTs之间产生了化学接枝作用,高分辨透射电镜分析表明两亲性聚合物不均匀地存在于MWNTs的表面和端部.两亲性聚合物的浓度对接枝量的影响不大,但超声波作用时间对MWNTs表面两亲性聚合物PVP的接枝量有较大的影响,在超声时间为4h时接枝量最大.两亲性聚合物修饰效果不同于表面活性剂,采用表面活性剂十二烷基苯磺酸钠(SDBS)修饰的MWNTs经过洗涤过滤后,不能重新溶于水中,而两亲性聚合物PVP修饰的MWNTs可以重新溶解.     

表面活性剂对分散体系粘度影响的特殊性

通过液体石蜡的水基化分散对影响分散体系粘度的粒子大小、表面活性剂胶束和界面膜等因素进行了研究.结果表明,表面活性剂胶束对分散体系粘度的影响极为有限,而在分散相粒子界面上由表面活性剂分子所形成的界面膜是导致分散体系粘度产生变化的重要因素.实验数据表明,对于分散体系的稳定性,存在一个表面活性剂浓度变化的临界值,而该临界值所对应的是表面活性剂分子在粒子表面以最紧密和规整的方式形成的界面膜,该种界面膜使分散体系粘度达到最大值,从而最大限度地保证了分散体系的稳定性.     

单分散磁性P(St/BA/MAA)微球的制备

在共沉淀法合成超细磁流体的基础上 ,以苯乙烯 (St)、丙烯酸丁酯 (BA)和甲基丙烯酸 (MAA)为共聚单体 ,在不同的介质体系中采用无皂乳液聚合法制备了单分散 ,粒径范围为 80～ 2 30nm的磁性P(St BA MAA)微球 .详细探讨了介质极性、磁流体中表面活性剂含量对磁性高分子微球粒径和单分散性的影响 .实验结果表明 ,在一定范围内随介质极性降低 ,磁性高分子微球的单分散性提高 ,随表面活性剂用量增加 ,单分散性变差 .总体来看 ,磁性高分子微球的单分散性与其表面静电斥力密切相关 ,过大或过小的静电斥力均会导致磁性高分子微球单分散性的降低 .     

Uniform directional alignment of single-walled carbon nanotubes in viscous polymer flow

In this work, we probed the effects of shear flow on the alignment of dispersed single-walled carbon nanotubes in polymer solutions. Two different systems were compared: Single-walled carbon nanotubes dispersed using an anionic surfactant and single-walled carbon nanotubes dispersed using an anionic surfactant and a weakly binding polymer. It was determined that the addition of the weakly binding polymer increased the degree of dispersion of the carbon nanotubes and the ability to induce their alignment when subjected to shear forces.     

Influence of Electric Field on Dispersion of Carbon Nanotubes in Liquids

Production processes for carbon nanotubes commonly produce mixtures of solid morphologies that are mechanically entangled or that self‐associate into aggregates. The entangled or aggregated carbon nanotubes often need to be dispersed in corresponding material matrices in order to develop materials that have unique mechanical characteristics or transport properties. The most effective method for dispersion of carbon nanotubes is to prepare fluid suspensions of them in liquid media with applications of surfactant or/and ultrasonication. The authors propose an innovative dispersion method for carbon nanotubes by which an electric field is applied to suspensions of carbon nanotubes in liquids treated by surfactant and ultrasonication. Compared to dispersion without the electric field, the dispersion status of carbon nanotubes in liquid media is evidently improved with the electric field. The results indicate that the electric field conditions are effective for dispersion of carbon nanotubes in liquids and that complex effects of electric field, surfactant, and ultrasonication are beneficial for improvement of dispersion of carbon nanotubes.     

An explanation of dispersion states of single-walled carbon nanotubes in solvents and aqueous surfactant solutions using solubility parameters

Dispersions of single-walled carbon nanotubes in various solvents and aqueous surfactant emulsions were investigated to correlate the degree of dispersion state with Hansen solubility parameters (deltat2=deltad2+deltap2+deltah2). It was found that the nanotubes were dispersed or suspended very well in the solvents with certain dispersive component (deltad) values. They were precipitated in the solvents with high polar component (deltap) values or hydrogen-bonding component (deltah) values. The solvents in the dispersed group occupied a certain region in a 3-dimensional space of three components. The surfactants with a lipophilic group equal to and longer than decyl, containing 9 methylene groups and 1 methyl group, contributed to the dispersion of nanotubes in water. The surfactants in the dispersed group had a lower limit in the dispersive component (deltad) of the Hansen parameter.     

Mechanism of carbon nanotube dispersion and precipitation during treatment with poly(acrylic acid)

Carbon nanotubes have been shown to be easily dispersed within an acidic aqueous solution of poly(acrylic acid) but precipitate when the pH is increased. Transmission electron microscopy showed that the nanotubes were more exfoliated under the acidic condition but highly aggregated under the basic condition. Carbon K‐edge NEXAFS spectroscopy showed that the carbon nanotubes did not chemically react with poly(acrylic acid) during the dispersion or precipitation and that the dispersion mainly involved physical adsorption of poly(acrylic acid) onto the nanotubes. Together with the carbon K‐edge NEXAFS spectra, the cobalt L_{3, 2}‐edge NEXAFS spectra suggested that under the basic condition, the cobalt impurity within the nanotubes strongly reacted with poly(acrylic acid) resulting in complex formation. Cobalt reduces the adsorption of poly(acrylic acid) onto the nanotubes, which then reduced the nanotube dispersion and resulted in the precipitation. Copyright © 2008 John Wiley & Sons, Ltd.     

Tuning the Dispersibility of Carbon Nanostructures from Organophilic to Hydrophilic: Towards the Preparation of New Multipurpose Carbon‐Based Hybrids

The hydroxyphenyl derivatives of carbon nanostructures (graphene and carbon nanotubes) can be easily transformed into highly organophilic or hydrophilic derivatives by using the ionic interactions between the phenolic groups and oleylamine or tetramethylammonium hydroxide, respectively. The products were finely dispersed in homo‐polymers or block co‐polymers to create homogeneous carbon‐based nanocomposites and were used as nanocarriers for the dispersion and protection of strongly hydrophobic compounds, such as large aromatic chromophores or anticancer drugs in aqueous solutions.     

Surfactant dispersed multi-walled carbon nanotube/polyetherimide nanocomposite membrane

Carbon nanotube based nanocomposite membranes have been fabricated through solution casting by embedding multi-walled carbon nanotubes (MWCNTs) within polyetherimide (PEI) polymer host matrix. In order to achieve fine dispersion of nanotubes and facilitate strong interfacial adhesion with the polymer matrix, the nanotubes were first treated with surfactants of different charges, namely anionic sodium dodecyl chloride, cationic cetyl trimethyl ammonium chloride and non-ionic Triton X100, prior to the dispersion in the PEI dope solution. Dispersion of MWCNTs in N-methyl-2-pyrrolidone solvent showed that the agglomeration and entanglement of the nanotubes were greatly reduced upon the addition of Triton X100. Scanning electron microscopy and atomic force microscopy examination has evidenced the compatibility of Triton X100 dispersed MWCNTs with the polymer matrix in which a promising dispersion and adhesion has been observed at the MWCNT-PEI interface. The increase in both thermal stability and mechanical strength of the resulting Triton X100 dispersed MWCNT/PEI nanocomposite indicated the improved interaction between MWCNTs and PEI. This study demonstrated the role of Triton X100 in facilitating the synergetic effects of MWCNTs and PEI where the resulting composite membrane is anticipated to have potential application in membrane based gas separation.     

Polymer-assisted dispersion of single-walled carbon nanotubes in alcohols and applicability toward carbon nanotube/sol-gel composite formation

Single-walled carbon nanotubes (SWCNTs) were directly dispersed into various alcohols by sonicating the nanotubes in the presence of poly(4-vinylpyridine) (P4VP). Depending upon the alcohol, it was possible to disperse up to 0.3 g of SWCNTs per liter of alcohol using only 0.6 g of P4VP, and with solution stability greater than 6 weeks. Scanning electron microscopy of "bucky" paper prepared from the polymer-treated nanotubes revealed reduced bundle size compared to the corresponding untreated nanotube paper. Additionally, the applicability of the dispersion system in the formation of SWCNT/silica composites is demonstrated.     

Synthesis of block polyethers with various structures and their application in dispersing single-walled carbon nanotubes

The block polyethers with different structure and composition were synthesized by anionic polymerization and used to disperse single-walled carbon nanotubes (SWNTs). The block polyethers with the structure of branch or benzene ring had better dispersion ability than the commercial Pluronic block polyethers (L64 and F127). In order to compare the parameters, dispersion limit and efficiency of polyethers for SWNTs were defined. UV?Cvis?Cnear infrared absorbance spectra showed that eight-branch polyether AE82 had much larger dispersion limit and efficiency than five-branch AE52. BPE containing benzene rings in the molecule had a slightly lower dispersion limit but larger dispersion efficiency than AE82. The defect density of SWNTs dispersed in polyether aqueous solutions was investigated by Raman spectroscopy. The polyethers AE83 and BEP with the structure of poly(ethylene oxide)?Cpoly(propylene oxide) dispersed less defective SWNTs than AE82 and BPE, indicating that the variation of polyether structure and composition could influence the defect density of SWNTs besides dispersion limit and efficiency.     

Surfactant-coated carbon nanotubes as pseudophases in liquid-liquid extraction

The advantages of surfactant-coated carbon nanotubes (CNTs) as coadjutants in liquid-liquid extraction are systematically considered. The effect of the CNT state (dispersed or suspended in an aqueous medium) is characterized by the single-component solid-liquid isotherms exemplified for benzene. Adsorption isotherms are obtained by means of a headspace-GC-MS method, the recommended instrumental combination when very volatile compounds are involved. Adsorption studies are completed using toluene and n-undecane as model analytes of aromatic and linear hydrocarbons, respectively. The potential of using dispersed carbon nanotubes to improve liquid-liquid extraction is finally evaluated. The liquid-liquid distribution of the two model analytes between an organic phase (n-heptane) and the aqueous dispersion of CNTs is studied via batch extraction and subsequent analysis of the organic phase by GC-MS. A prospective application of this methodology is also given.     

Single wall carbon nanotube supports for portable direct methanol fuel cells

Single-wall and multiwall carbon nanotubes are employed as carbon supports in direct methanol fuel cells (DMFC). The morphology and electrochemical activity of single-wall and multiwall carbon nanotubes obtained from different sources have been examined to probe the influence of carbon support on the overall performance of DMFC. The improved activity of the Pt-Ru catalyst dispersed on carbon nanotubes toward methanol oxidation is reflected as a shift in the onset potential and a lower charge transfer resistance at the electrode/electrolyte interface. The evaluation of carbon supports in a passive air breathing DMFC indicates that the observed power density depends on the nature and source of carbon nanostructures. The intrinsic property of the nanotubes, dispersion of the electrocatalyst and the electrochemically active surface area collectively influence the performance of the membrane electrode assembly (MEA). As compared to the commercial carbon black support, single wall carbon nanotubes when employed as the support for anchoring the electrocatalyst particles in the anode and cathode sides of MEA exhibited a approximately 30% enhancement in the power density of a single stack DMFC operating at 70 degrees C.