【作者】 庄文昌；

【导师】 陈晓；

【作者基本信息】 山东大学 ， 物理化学， 2008， 博士

【摘要】 纳米结构材料由于自身尺寸大小而具有独特的物理化学性质,成为当前材料研究最活跃的领域之一。其中,以纳米粒子为代表的“硬材料”,在光学、电子、磁学、催化、传感器等领域具有广泛的应用前景;而以溶致液晶为代表的“软物质”,则对新型功能纳米材料设计与制备、复合材料开发、生物催化及药物纳米控释等方面有重要意义。纳米材料的发展和纳米理论的完善越来越依靠于各种先进的测试方法和科学仪器,而小角X射线散射（SAXS）作为一种非破坏性原位观测方法,已成为当前非晶纳米结构材料研究的强有力工具。本文将主要利用SAXS技术,一方面分析纳米粒子分散体系的尺寸形貌,为纳米材料的制备、结构和尺寸的调控以及在溶剂中的分散状态提供重要信息;另一方面,对形貌多样的各类有序分子组合体进行结构解析,获悉体系中各组分分子的相互作用和各种双亲分子的自组装形式,从而阐明有序分子组合体构建和结构变化的机理。研究内容主要包括三部分:第一部分,采用液相还原法分别制备无包覆型、油酸钠（SO）包覆型和十六烷基三甲基溴化铵（CTAB）包覆型Ag、Au纳米粒子水溶胶以及核壳型γ-Fe₂O₃@Au纳米粒子水溶胶,通过调节反应物配比、反应时间、反应温度等得到了粒径分布比较均匀、稳定性良好的水溶性纳米粒子。论文主要利用SAXS手段结合紫外-可见吸收光谱（UV-vis）、透射电镜（TEM）、核磁共振（NMR）、差示扫描量热（DSC）和电泳等测试技术对纳米粒子粒径分布、包覆状态、带电性和界面结构进行了深入研究,建立了纳米粒子在溶胶中的分散和包覆模型。与无包覆状态的纳米粒子相比,SO包覆可使纳米粒子带有负电,CTAB包覆的纳米粒子则带有正电;两种包覆剂可使纳米粒子的UV-vis光谱最大吸收波长发生不同程度的红移。将纳米溶胶的SAXS曲线进行Guinier计算,得到的纳米粒子在溶胶中的平均粒径普遍大于TEM测得的干态粒径,其差值与包覆层厚度接近;通过对曲线进行Porod计算,发现表面具有包覆剂的Ag、Au纳米粒子的Porod曲线出现正偏离,表明包覆剂在金属表面的吸附引发了电子密度不均匀微区的形成。其中,对利用银氨络合方法制备得到的CTAB包覆的表面正电型Ag纳米粒子研究发现,CTAB是通过头基包覆在银核表面并且为双层包覆结构。对于核壳型γ-Fe₂O₃@Au纳米粒子,利用UV-vis和X射线衍射证实在γ-Fe₂O₃的表面已包覆上了金壳;SAXS结果得到其平均粒径约为50 nm;与Ag、Au纳米粒子不同,核壳型纳米粒子的Porod曲线呈现负偏离,表明在γ-Fe₂O₃核与水之间存在一个Au的过渡层,由此得出Au包覆层厚度。该工作利用SAXS对纳米粒子在水溶胶中分散状态快速而精确地测定,为人们深入开展纳米粒子的液相合成和结构调控提供了重要的参考信息,也为湿态纳米材料结构表征和分析提供了一条快捷而有效的途径。论文第二部分,利用离子型表面活性剂构建溶致液晶相结构,对比考察了双烷基链阴离子型表面活性剂琥珀酸二异辛酯磺酸钠（AOT）和单烷基链阳离子型表面活性剂CTAB在水/醇中的自组装行为,系统探讨了长烷基链离子液体（IL）与传统表面活性剂复配对溶致液晶相结构的影响。通过SAXS实验发现,随着AOT浓度的增加,AOT/水体系逐渐由胶束相形成层状相,AOT分子在体系中的排列更为紧密,从而使层状相的有序性逐渐提高;固定表面活性剂浓度、升高温度或者加入一定的助表面活性剂（如短链醇）,可减小AOT分子头基在极性/非极性界面的有效面积,或提高表面活性剂的疏水体积,有利于层状结构有序性的提高。研究过程中注意到,AOT质量分数为0.4时SAXS散射曲线一级峰消失。根据这一结果,并结合耗散粒子动力学（DPD）分子模拟方法,充分研究了层状相有序性提高过程中的结构变化。通过对层状相结构中水扩散率的研究,证实了结构变化过程中层状相存在的结构缺陷—准反六角相。所得结果进一步提升了人们对层状相中缺陷结构的认识。与AOT分子不同,CTAB在水中可自组装形成六角相结构,加入一定浓度的辛醇可实现六角相向层状相的结构转变。在解析溶致液晶相微观结构的基础上,将不同烷基链长、具备不同阴离子的烷基咪唑类IL与CTAB复配,通过SAXS研究表明:[C₁₆mim]Cl与CTAB具有良好的复配性能,两种分子可以较好的结合在一起构建溶致液晶,同时对温度变化也有一致的协同响应;改变IL烷基链链长,由于[C₈mim]Cl烷基链较短而头基相对较大,更易与水接触形成胶束相,与CTAB复配后在较低的浓度下即可破坏体系的层状相和六角相结构;最后,通过替换不同的阴离子（用PF₆^-和BF₄^-替换Cl^-）进一步改变离子液体与CTAB、水之间的相互作用,发现复配体系出现了相分离（下层为溶致液晶相,上层为离子液体溶液相）,其中溶致液晶中也易形成多种相态（层状相、六角相和立方相）共存的结构。该工作对阐明离子型表面活性剂自组装机理具有重要意义,同时也对提高此类溶致液晶结构的有序性提供了有价值的参考。率先开展的IL与传统表面活性剂复配构建溶致液晶的探索,将有助于人们对长烷基链离子液体与传统表面活性剂相互作用的认识,并有利于拓展离子液体构建有序结构材料的应用范围。第三部分,深入开展了在环境友好型溶剂—离子液体中构建溶致液晶相的研究,分别采用了两种具有不同亲疏水性能的IL,亲水的1-丁基-3-甲基咪唑四氟硼酸盐（Bmim-BF₄）和疏水的1-丁基-3-甲基咪唑六氟磷酸盐（Bmim-PF₆）,与水组成溶剂构建新型溶致液晶材料;探讨了非离子型表面活性剂Brij-30和双亲嵌段共聚物PEO-PPO-PEO在混合溶剂中的相行为,并对其相互作用机理进行分析。通过对各种体系相结构参数的解析,发现:双亲分子中的烷基链或PPO基团和亲水PEO基团与IL中的阴阳离子之间存在多种相互作用（与烷基链或PPO基团之间的疏溶剂作用、与PEO形成的氢键）,是有序液晶结构形成的关键;IL阳离子所具有的丁基链与双亲分子疏溶剂基团的协同作用有利于形成极性/非极性界面,并且IL作为一种熔融盐会起到一定的盐析效应,也促进了自组装结构的形成。在Brij-30/水所形成的层状结构中加入IL,可使表面活性剂分子以一种更加松散的方式进行堆积;Bmim-PF₆分子主要处于Brij-30的极性EO基团区域,而Bmim-BF₄既可处于EO区域也可与水形成溶剂区域;通过DSC和SAXS变温实验,证明在低温下层状相结构中出现一个准六角相结构,而在高温下则出现反相胶束结构。同时,含Bmim-PF₆体系可有效增强体系的热稳定性。与Brij-30体系主要以层状结构为主不同,嵌段共聚物P123体系以层状相和六角相为主,而F127则以六角相和立方相为主。实验发现,嵌段共聚物体系中不存在独立的溶剂区域,因而形成的溶致液晶相并不遵循“溶胀定律”;含Bmim-BF₄体系中相同结构的液晶相区域都是连续的,而P123/Bmim-PF₆/H₂O体系中由于Bmim-PF₆和水不能互溶所以除层状相外,六角相、立方相都分别被分割为两部分;其中层状相可连续存在的原因是:体系中存在双层状结构可将两种溶剂分割。此外,在F127Bmim-PF₆/H₂O和F127/Bmim-BF₄/H₂O体系中还分别存在双连续立方相和四方相,而且四方相具有两种构型:穿孔的层状型和胶束四方堆积型。该工作不仅在离子液体中构建了新型有序纳米结构,而且丰富的溶致液晶结构的解析有助于探索这类有序聚集体在作为绿色模板和微反应器方面的应用,也有利于寻求对分子间非共价键弱相互作用（氢键、配位键、亲/疏溶剂相互作用及它们之间的协同作用等）更深层次的探讨。更多还原

【Abstract】 Owing to the unique size-dependent chemical and physical properties,the study of nanostructured materials has become one of the most active research fields.On the one hand,Nanoparticles as one kind of "hard materials" have been widely applied in the fields of photonics,electronics,magnetics,catalytic,etc.On the other hand Lyotropic liquid crystal（LLC）as a representative of "soft matter",pay great important role in novel functional nanostructure materials design,device hybrid materials development,biocatalysis and drug nano-controlled release.Now,the developments of nanomaterials and correlative theory rely increasingly on a variety of advanced testing methods and scientific equipments. Thereinto,small-angle X-ray scattering（SAXS）as a non-destructive and in-situ method,has become a powerful research tool in colloid dispersive systems and organized molecular assemblies.In this dissertation,SAXS is utilized to analyze the size and morphology of nanoparticles.Furthermore,it is also applied to characterize the structures of various LLC and the self-assembled form of surfactant.This dissertation consists of three main parts.In the first part,noble metal（Ag,Au）nanoparticles with different surface properties as well as core-shell shapedγ-Fe₂O₃@Au nanoparticles are prepared in aqueous phase.Different surfactant molecules such as cetyltrimethylammonium bromide（CTAB）and sodium oleate（SO）are selected as capping agent to fabricate positivelyly or negativelyly charged particles.Based on SAXS data,products’ morphology and size distribution are characterized through many different analytical ways such as UV-visible spectrum（UV-vis）,Transmission Electronic Microscopy （TEM）,Fourier-transformed infrared spectroscopy（FTIR）,nuclear magnetic resonance（NMR）,differential scanning calorimetry（DSC）and thermal gravimetric analysis（TGA）.SAXS are also adopted to investigate particles’ surface properties.Compared with non-coated nanoparticles,red shifts have been observed in UV-vis absorption band for CTAB-coated and SO-coated particles.According to the Guinier curves of SAXS data,the average sizes of coated particles in the sol are larger than those measurements by TEM,where the margins are close to the coating thicknesses.Moreover,positively deviations from Porod’s law occur for coating particles because of density fluctuation which derive from thermal electron movement or compositional heterogeneity within phases.Through SAXS and other measurements,CTAB-coated Ag nanoparticles,which were prepared successfully by a classical method to change silver nitrate to diamminesilver ion to avoid AgBr formation before reduction,are confirmed that CTAB molecules cap Ag core via their headgroups and form a bilayer shell on the surface of Ag clusters.It have also been proved thatγ-Fe₂O₃ is coated by Au shell about 13.8 nm thickness calculated from a Porod’s negatively deviation curve which attribute to the interlayer within phases and the average size of core-shell shaped nanoparticles is about 50 nm.Obtained results suggest that the dispersion state of nanoparticles in the sol can be determined quickly and accurately through SAXS technique,which will provide important reference information on preparation of nanoparticles in solution as well as a quick and effective way for wet-nanomaterials characterization and analysis.In the second part of dissertation,LLC phases made of ionic surfactant is formed with the aim to systematically study the self-assembly structures of anion surfactant sodium bis（2-ethylhexyl）sulfosuccinate（AOT）with two alkyl chains and cation surfactant CTAB with single alkyl chain.Furthermore,various ionic liquids （IL）with long alkyl chain,which can be regarded as a special surfactant,are introduced to explore the blending compatibility with conventional surfactant.In the AOT/H₂O lamellar phase,its structure can be tuned by surfactant concentration,temperature or adding cosurfactant.Based on SAXS data,the structural transformation from micelle to lamellar phase with increasing AOT concentration is investigated,meanwhile the arrangement of hydrocarbon chains will change from sparse to dense status and the ordering of LLC will be improved.The higher ordering of LLC will also be obtained through increasing temperature or adding short-chain alcohols in a certain range,which will result in a smaller effective area of AOT molecules in the polar/apolar interface or a larger hydrophobic volume of surfactant.However,there is an abnormal structure when the AOT concentration is 40 wt%,where the 1^stscattering peak is missing because of deformed lamellar structures.Thus the structural transition in the process of ordering improvement is researched using SAXS and Dissipative Particle Dynamics（DPD）methods.It is proposed that at about 40%concentration,a defective structure,pseudo-reversed hexagonal phase,is formed to evidently decrease the water diffusivity,which might produce some mesophase property changes,such as reduction of the liquid crystalline long-range order.Unlike the AOT/H₂O system,CTAB will form hexagonal structure in aqueous solution as well as lamellar phase by adding a certain concentration of 1-octanol.On the basis of detailed analysis of structural parameters,the blending compatibility between IL and CTAB is discussed.It conclude from SAXS results that[C₁₆mim]Cl has good compatibility and consistent coordinated response for temperature with CTAB so as to from homogeneous LLC.Nevertheless,the LLC structures will break up to from micellar phase when blending[C₈mim]Cl at lower concentration with CTAB for shorter alkyl chain of IL.Finally,phase separations take place in the blending system of CTAB and IL when substituting PF₆^- and BF₄^- for Cl^-,where the upper phase is IL solution and the lower phase is LLC which comprises of multistructures such as lamellar,hexagonal and cubic arrays.These results will be helpful to illuminate the mechanism of ionic surfactant self-assembly and provide valuable reference for improving the ordering of LLC. Initial exploration for the blending compatibility between IL and conventional surfactant will be beneficial to understand the interaction of such amphiphilic molecules and enlarge the ILs’ application in ordering structural materials.At last,LLC formed in IL named novel environmentally friendly solvent will be deeply investigated in this paper.Two typical imidazolium salts,the hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate（Bmim-BF₄）and the hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate（Bmim-PF₆）,are chosen to fabricate various liquid crystal phases in aqueous solution respectively with three kind of nonionic amphiphilic molecules,viz.Brij-30（tetraethylene glycol lauryl ether）,P123(EO₂₀-PO₇₀-EO₂₀)and F127(EO₁₀₀-PO₇₀-EO₁₀₀).The phase behaviors of those systems and the interactions between such molecules are fully discussed.In IL-containing systems,various interactions between EO-ILs（hydrogen bonding）and lipotropy-ILs（hydrophobic interaction）play key roles in LLC formation.Additionally,the cation[Bmim]⁺ with a hydrophobic butyl group tends to act as a cosurfactant and cooperate with the block copolymer in forming interfaces, thus enhancing the structural order.And also,as a melting salts,the ionic liquid（IL） may have a salting-out effect on the block copolymer system,which is helpful for formation of self-assembled structures.The good stability of such system is due to strong interactions mentioned above.According to the structural parameters of LLC derived from SAXS measurement,the stacking of surfactant molecules will be in a looser manner when doping ILs into Brij-30/water lamellar phase.The difference of amphiphilic nature between two used ILs makes Bmim-PF₆ tend to stay at the interface of polar/apolar section,whereas Bmim-BF₄ molecules like to locate in water regions as well as in polar domains.The additional thermal analyses by DSC and SAXS suggest a pseudo-hexagonal columnar structure appeared at low temperature in Brij-30/IL/H₂O ternary systems,while the reverse micelle at high temperature.There are mainly lamellar and hexagonal phase formed in P123/IL/H₂O systems,however hexagonal and cubic phase are dominant in F127/IL/H₂O systems.Bi-lamellar structures are observed in P123/Bmim-PF₆/H₂O ternary system,which keep a continuous lamellar region with the change of content ratio of Bmim-PF₆ and H₂O.Furthermore, bicontinuous cubic and tetragonal phase are also obtained respectively in F127/Bmim-PF₆/H₂O and F127/Bmim-PF₄/H₂O.Our effort for fabricating organized molecular assemblies in ILs will be beneficial to the application of such self-assemblies as "green" template and micro-reactor,furthermore it is helpful to deeply discuss the weak non-covalent interactions for molecules.Special thanks are due to the National Natural Science Foundation of China for financial support（20373035,20573066,20773080）.更多还原