【作者】 李洪光；

【导师】 郝京诚；

【作者基本信息】 山东大学 ， 胶体与界面化学， 2008， 博士

【摘要】 富勒烯和碳纳米管结构新颖,性质独特,应用前景极为广阔。然而水溶性差、容易聚集等问题大大阻碍了对其深入的研究和实际应用。胶体与界面化学的研究,特别是表面活性剂溶液有序聚集体的研究,为解决上述难题提供了新的思路和手段。论文以十四烷基三甲基氢氧化铵（TTAOH）和月桂酸（LA）复配得到的无盐阴/阳离子表面活性剂混合体系为主线,详细研究了其水相和非水相性质和相行为,并在此基础上系统研究了富勒烯C₆₀,C₆₀/C₇₀混合物在TTAOH/LA/H₂O体系中的增溶及其碳纳米管的稳定分散;同时系统研究了一系列亲水基团修饰的C₆₀衍生物水相中的聚集行为及其与表面活性剂和碳纳米管的相互作用。论文的具体内容如下:第一章分别从表面活性剂物理化学和富勒烯化学的角度,简要介绍了国内外相关研究背景,阐述了论文选题的科学意义。第二章系统研究了TTAOH/LA/H₂O体系的相行为和流变学性质,绘制了三元相图。研究发现,随着LA和TTAOH混合比例(n_LA/n_TTAOH)和表面活性剂总浓度(c_TTAOH+LA)的变化,体系表现出丰富的相行为。当TTAOH过量时,在n_LA/n_TTAOH＜0.87时形成各向同性的L₁相（胶束相）,其粘度随样品组成的不同而有很大变化。随着LA含量的增加,具有双折射现象的L_α相开始形成,在某些区域,L₁相和L_α相共存,上部双折射的L_α相与下部各向同性的L₁相之间有明显的界面,两者的体积比随着样品的组成而变化。在LA和TTAOH混合比例接近和达到1∶1以及LA稍过量时,形成了淡蓝色的囊泡相。其中高浓度的囊泡相具有明显的双折射现象,而浓度较低时,双折射现象不明显。另外,在表面活性剂总浓度极低时,体系容易发生宏观相分离,且这一现象随着n_LA/n_TTAOH值的增大而变得尤其明显。TTAOH/LA/H₂O体系丰富的相行为是微观上各种聚集体生长和相互演变的宏观反映,这种生长和演变也导致了体系流变学行为的变化。以表面活性剂总浓度为25 mg/mL的系列样品为例,随着n_LA/n_TTAOH的变化,可依次观察到牛顿流体区,剪切增稠区,具有Maxwell流体特性的蠕虫状胶束区和弹性模量远大于粘性模量、具有屈服应力的密堆积囊泡区。我们分别对各相区的稳态剪切和振荡剪切特性进行了深入研究和探讨,同时考察了温度的影响。结果表明,升高温度大大抑制胶束的生长,使样品失去粘弹性,但对囊泡相却影响不大。此外,对L₁/L_α两相共存区相分离前后的流变学性质以及剪切和时间诱导的双折射L_α相的偏光织构也进行了研究。第三章系统研究了TTAOH/LA混合体系在多种有机溶剂中的性质,在合适的表面活性剂组成和少量水存在的情况下,构筑了反相囊泡并详细研究了反相囊泡的性质和在模版合成无机纳米粒子方面的潜在应用价值。反相囊泡样品由于对自然光的散射而呈现蓝色,偏光显微镜观察表明它们具有明显的双折射纹理,直径可达微米数量级。深入研究发现,反相囊泡的性质及稳定性与所用溶剂和温度密切相关。在环已烷和苯类溶剂如甲苯及第三丁基苯中,反相囊泡的形成是自发的且具有很高的稳定性,而在烃类溶剂如庚烷中,反相囊泡的形成往往需要外力的帮助,而且不够稳定,随时间的延长或离心力的增加而发生宏观相分离。反相囊泡对温度变化非常敏感,升高温度会导致形成反相囊泡的表面活性剂组成向着LA含量高的一端移动,反之亦然。向反相囊泡溶液中加入少许含无机离子如Zn²⁺,S^2-等的水溶液不会破坏其结构,但过多无机离子的引入会导致反相囊泡结构的消失。通过小心控制实验条件,反相囊泡可以作为模版用来合成特定形貌的无机纳米粒子。我们在这方面进行了初步尝试,取得了一些阶段性成果。第四章系统研究了富勒烯C₆₀和C₆₀/C₇₀混合物在TTAOH/LA/H₂O体系中的增溶以及增溶后C₆₀吸收光谱和富勒烯增溶诱导的混合体系宏观相行为的变化。增溶过程经历了一个中间步骤,即首先使富勒烯和表面活性剂分子在富勒烯良性溶剂甲苯中达到分子水平的均匀混合。研究发现,TTAOH/LA/H₂O体系尤其是等摩尔量混合时形成的囊泡相有可观的增溶富勒烯的能力。例如,对于等摩尔量混合时50 mmol/L的囊泡相,当增溶C₆₀的浓度达到0.588 mg/mL时仍然没有发生宏观相分离。而此前文献报道的表面活性剂水体系中C₆₀的最大增溶量仅为0.4mg/mL。对TTAOH/LA/H₂O体系其它相区的研究表明,双折射L_α相也具有可观的增溶富勒烯的能力,相比之下,L₁相尤其是粘弹性的蠕虫状胶束增溶富勒烯的能力较弱。当LA过量时,样品随着n_LA/n_TTAOH的增大逐渐失去增溶富勒烯的能力。对增溶富勒烯后混合体系宏观相行为的研究表明,将样品稀释时,富勒烯和一部分表面活性剂会沉淀出来,生成沉淀的量随样品的持续稀释而增加。相对于囊泡相,胶束相的抗稀释能力较强。研究还发现,C₆₀增溶后紫外-可见特征吸收光谱消失,吸收曲线发生红移,整体向长波方向移动。与此相伴随的是混合体系颜色的变化。深入研究发现样品颜色变化和C₆₀吸收光谱消失的速度与光照和氧气的存在无明显关系,而随着混合表面活性剂中TTAOH含量的增加而加快。分析后认为,除了C₆₀分子间的团聚,增溶过程中C₆₀分子与OH^-之间很可能发生了某种电子转移反应。第五章借助PEO-PPO-PEO三嵌段共聚物F127和聚乙烯吡咯烷酮（PVP）将碳纳米管稳定分散于TTAOH/LA/H₂O体系中,并详细研究了聚合物的加入和碳纳米管的分散对TTAOH/LA/H₂O体系流变学性质的影响,同时研究了分散后碳纳米管的紫外-可见-近红外吸收光谱的特征。对TTAOH/LA/H₂O体系剪切增稠区、蠕虫状胶束区和囊泡区的流变学测量表明,聚合物尤其是F127的加入大大抑制了聚集体的生长,表现为体系粘度的下降和弹性的丧失。在聚合物加入质量相等的情况下,F127的影响明显大于PVP,这一结论也为表面张力的测定结果所证实。这主要是由于F127与TTAOH/LA/H₂O体系之间存在较强的疏水相互作用且能够形成氢键的缘故。研究发现,TTAOH/LA/H₂O体系本身不具备良好的分散碳纳米管的能力,然而在聚合物F127和PVP的帮助下,碳纳米管能够很好地分散于混合体系中。紫外-可见-近红外吸收光谱研究结果表明,碳纳米管的分散效果随聚合物加入量密切相关。流变学的测量结果表明,碳纳米管的掺杂使混合体系的粘弹性降低,弛豫时间变长。第六章系统研究了两种树枝状单加成羧酸类C₆₀衍生物（1,2）、三种星状[3∶3]六加成季铵盐类C₆₀衍生物（3,4,5）和两种星状[3∶3]六加成羧酸类C₆₀衍生物（6,7）的水溶液性质和聚集行为,以及它们与表面活性剂和碳纳米管的相互作用。1和2具有很高的水溶性,紫外-可见吸收光谱和动态激光光散射的研究结果表明它们在水中均能够发生一定程度的自聚集,但不同亲水枝的接入导致它们的自聚集行为有所不同。随着阳离子表面活性剂TTAOH的加入,1和2的自聚集行为变得异常显著,以致出现沉淀。对上清液的冷冻刻蚀电子显微镜的观察发现了单层囊泡的存在。3-5也具有很高的水溶性,在水溶液中的自聚集行为不显著。但它们仍然具有两亲性,且能够分散碳纳米管。6和7能够很好地溶解于中性尤其是弱碱性缓冲溶液中,但在纯水中的溶性性极差。当加入适量NaOH,使它们转变为相应的钠盐6-Na和7-Na后,水溶性大大提高。通过研究1-5以及6-Na和7-Na水溶液中自聚集行为得出的共同结论是它们的亲水基团过于庞大而疏水基团偏小,分子的HLB值偏大,自聚集行为不显著。此外还研究了高离子强度水溶液中1,2,6-Na和7-Na的自聚集行为,电子显微镜观察得到了形貌多样的聚集体。更多还原

【Abstract】 As novel nanostructures,fullerenes and carbon nanotubes are known to have many unique properties and great potential applications.However,their poor solubility in water together with their propensity to form large aggregates has long been an obstacle for further study and practical applications.To solve these problems,the means originating from colloid and interface science especially those from surfactant science are frequently adopted.In this doctoral dissertation,the detailed phase behavior of tetradecyltrimethylammonium hydroxide（TTAOH）/lauric acid（LA）surfactant mixture has been investigated both in aqueous and non-aqueous media.After that.this mixed surfactant system is selected to solubilize fullerene C₆₀and C₆₀/C₇₀mixture as well as to disperse carbon nanotubes.In addition to improve the solubility of pristine fullerenes and carbon nanotubes in aqueous media,we have also investigated the properties and aggregation behavior in water of some C₆₀amphiphiles given by Andreas Hirsch from Germany.The interactions between these C₆₀amphiphiles and traditional surfactants as well as carbon nanotubes are also discussed.The outline and contents of this doctoral dissertation are as follows:ChapterⅠis a brief introduction of the research background of this work,in which the history and recent progress in surfactant science as well as fullerene chemistry are reviewed from a worldwide angle of view.The objective and the scientific significance of this doctoral dissertation are also pointed out at the end of this part.In ChapterⅡ,the phase behavior and rheological properties of TTAOH/LA/H₂O system are investigated in detail.It is found the system exhibits a rich phase behavior with the variation of molar ratio of LA to TTAOH(n_LA/n_TTAOH)and total surfactant concentration (C_TTAOH+LA)at 25℃.In TTAOH rich side,an isotropic L_l phase（micellar phase）forms at n_LA/n_TTAOH＜0.87.whose viscosity changes significantly with solution parameter.As n_LA/n_TTAOHincreases from the border of L_l phase,birefringent L_αphase begins to form.In certain region,L_l phase and L_αphase coexist with birefringent L_αphase at the top.An obvious interface can be found between bottom L_l phase and top L_αphase and the volume ratio of L_αphase to L_l phase varies with solution parameter.Around equimolar mixing ratio of LA to TTAOH,bluish vesicular phase is observed which extends to the region where LA is in slight excess.At low concentration of total surfactants,the system tends to macroscopically phase separate and this phenomenon will be more obvious at higher LA content.The rich phase behavior of TTAOH/LA/H₂O system with variation of solution parameter is a macroscopic reflection of aggregate growth and evolution among different kinds which occurs at microscopic length scale.The growth and evolution of aggregates also induce significant rheological property changes of the system.Take the series of samples with c_TTAOH+LA=25 mg/mL for example,a Newton fluid region,a shear-thickening region,a worm-like micellar region which exhibits Maxwell fluid character and a gel-like vesicular region are observed in turn with increasing n_LA/n_TTAOH. We have investigated the detailed rheological properties by means of both steady state and oscillatory measurements within each region as a function of total surfactant concentration and temperature.It is found micelle growth is greatly suppressed at higher temperatures while temperature rise has a much less influence on vesicular phases.The rheological property of the L_l and L_αphase within the two-phase region has been carried out as a whole as well as separately.The textures of the birefringent L_αphase are also investigated by a polarized microscope as a function of shear and time.In ChapterⅢ,the phase behavior of TTAOH/LA mixed system is investigated in various organic solvents.After monitoring the experimental conditions,reverse vesicles with dimensions usually at micrometer scale are successfully constructed in several non-polar organic solvents including toluene,tert-butyl benzene,cyclohexane and n-heptane.The formation of reverse vesicles occurs within a rather narrow range of surfactant composition and a small amount of water is always necessary.The reverse vesicular phases show a blue color against room light and exhibit strong birefringence under polarized microscope.It is found the property and stability of reverse vesicles depends greatly on the selected organic solvent and temperature.In toluene,tert-butyl benzene and cyclohexane,reverse vesicles can form spontaneously and show high stability at room temperature.An increase in temperature can make the composition of surfactants within which reverse vesicles are constructed move to LA-rich side and vice versa.In n-heptane,however,the formation of reverse vesicles usually needs external energy and these reverse vesicles are not stable at room temperature.Instead.they will disappear from the top upon time and centrifugation.Ultimately macroscopic phase separation is observed,which will be accelerated at higher temperatures,and a gel-like phase forms at the bottom.Reverse vesicles may not be destroyed if suitable amount of aqueous solutions containing certain inorganic ions such as Zn²⁺and S^2-is added,but adding too much will of course destroy the structure of reverse vesicles.By designing experiments with great care,reverse vesicles can be used as nano-reaction center for inorganic particle synthesis.Investigation toward this direction has also been carried out and some interesting results have been obtained.Based on the knowledge of TTAOH/LA mixed system both in aqueous and non-aqueous media obtained from the former two chapters,in ChapterⅣwe investigate the solubilization of fullerene C₆₀and C₆₀/C₇₀mixture in TTAOH/LA/H₂O system via a medium step where an organic solvent toluene is involved.The changes of spectral features of fullerenes before and after solubilization as well as fullerene solubilization induced phase behavior changes of the mixed system have also been clarified.It is found the solubilization capability is considerable high for the vesicular phases especially those formed at n_LA/n_TTAOH=1.For example,the 50 mmol/L vesicular phase at n_LA/n_TTAOH=1 Can solubilize C₆₀up to 0.588 mg/mL without macroscopic phase separation.This is already higher than the solubilization maximum of C₆₀in other surfactant systems reported in literatures,which is 0.4 mg/mL.Further investigations indicate the L_αphases also have considerable capability to solubilize fullerenes while the L_l phase especially the worm-like micellar phases can not effectively solubilize fullerenes.In LA rich side.the system loses the ability to solubilize fullerenes gradually with increasing n_LA/n_TTAOH.We have investigated the phase behavior of TTAOH/LA/H₂O system with fullerenes solubilized as a function of total surfaetant concentration.It is found precipitate will form when the samples are diluted by water and the amount of precipitate depends on the kind of phase as well as the extent of dilution.Compared with vesicular or lamellar phases. micellar phases with fullerenes solubilized are more stable against dilution. Thermogravimetric analysis indicates the precipitate is a mixture of fullerenes and surfactants rather than fullerenes only.UV-vis-NIR measurements indicate the characteristic absorptions of fullerenes disappeared after solubilization and an Einstein shift occurs for the whole absorption curve together with an interesting color change of the samples.Further investigations have revealed the color change of the samples and the disappearance of the characteristic absorptions of fullerenes are influenced little by light. but depends greatly on the content of TTAOH in total surfactants.So it seems that electron transfer reactions occur between fullerenes and OH^- during solubilization together with an aggregation of fullerene molecules.In ChapterⅤ,the dispersion of carbon nanotubes（CNTs）in TTAOH/LA/H₂O system is investigated at the presence of two kinds of nonionic polymers.Pluronic F127 and polyvinylpyrrolidone（PVP）.The rheological property changes of TTAOH/LA/H₂O system induced by polymer and CNTs addition are investigated in detail,respectively.The UV-vis-NIR measurements have also been carried out on the TTAOH/LA/polymer/CNTs mixed samples.It is found that the addition of polymers greatly suppresses aggregate growth both in micellar region and vesicular region,which can be seen simply by shaking. and visual inspection.This conclusion gains further proof from rheological measurements which are carried out on the shear-thickening region,the worm-like micellar region and the vesicular region.At the same weight fraction of polymers,the influence of F127 is much more obvious than that of PVP,which is also consistent with the results of surface tension measurements.This is due to the strong hydrophobic interaction as well as hydrogen bond formation between F127 and TTAOH/LA/H₂O system.TTAOH/LA/H₂O system itself can not disperse CNTs effectively.After addition of F127 or PVP.however. CNTs can be well dispersed into the bulk aqueous solutions.UV-vis-NIR measurements indicate the quality of the final dispersion is influenced greatly by the amount of added polymer.After introduction of CNTs into the matrix of ordered molecular assemblies such as worm-like micelles,the rheological properties of mixed system change obviously with a decrease in viscoelastic property and a rise in relaxation time.In the last chapter,we have investigated the properties and aggregation behavior in aqueous solutions of seven C₆₀amphiphiles with different molecular structures which are kindly given by Andreas Hirsch from Germany.The interaction between these C₆₀ amphiphiles and traditional surfactants as well as CNTs is also discussed.1 and 2 have 18 and 9 terminal carboxy groups as hydrophilic part,respectively,and are highly soluble in water.They belong to monoadducts of C₆₀derivatives and have a dendritic molecular structure.The aggregation behavior of 1 and 2 in water is not obvious as proved by transition electron microscopy（TEM）observations.UV-vis and dynamic laser light scattering（DLLS）measurements show,however,they can still form aggregates in water. This conclusion gains further proof from the fact that they can disperse MWNTs.It is found the aggregation behavior of 1 and 2 is different from each other due to their different hydrophilic parts.The aggregate formation of 1 and 2 can be greatly enhanced when a cationic surfactant,TTAOH is added.The[3:3]hexakisadducts of C₆₀amphiphiles 3-5 are star-like.They are also highly soluble in water and each has six terminal quartery ammonium headgroups together with different number of ethyloxide groups as hydrophilic part.Similar with 1 and 2,the aggregation behavior of 3-5 in water is not obvious,either.But they still exhibit moderate amphiphilic character in aqueous solutions as proved by surface tension measurements and can disperse CNTs which are rich in SWNTs.The[3:3]hexakisadducts of C₆₀amphiphiles 6 and 7 are also star-like.They have 6 and 18 terminal carboxy groups,respectively,and are almost insoluble in water but soluble in basic aqueous solutions.After being transformed into their corresponding sodium salts 6-Na and 7-Na,the solubility is greatly improved and they can be subsequently used to disperse MWNTs.Investigations have been carried out on the aggregation behavior of 1.2,6-Na and 7-Na in aqueous solutions containing highly concentrated salts and interesting fraetals are observed besides well-defined spherical aggregates.更多还原