【作者】 沈淑坤；

【导师】 胡道道；

【作者基本信息】 陕西师范大学 ， 有机化学， 2006， 硕士

【摘要】 有机修饰硅氧烷经由溶胶-凝胶过程制备化学稳定、光学透明、机械性能优越的有机-无机杂化材料是当今材料科学领域的研究热点之一。目前,这些杂化材料广泛地应用于光学器件、电子元件、化学/生物医学传感、催化、功能涂层和薄膜等领域。 在制备溶胶-凝胶材料的过程中,有机成分的引入主要通过内源性有机修饰及添加外源性有机物两种途径实现。不同于传统小分子前驱体的溶胶-凝胶过程,经过有机修饰的硅氧烷因为取代基结构和性质的差异会导致前躯体溶胶-凝胶过程的变化。取代基效应具体表现在对水解缩聚反应速度、产物分布、空间结构演化、存在状态、组织排布方式、产物微区环境的影响。外源性有机化合物引入到溶胶-凝胶体系也可以影响前驱体水解-缩聚的速度、调控溶胶粒子的生长尺度和方向、控制材料的外在形貌。借助这种影响可实现合成复合材料的多功能化,从而达到修饰、改性溶胶-凝胶材料的目的。因此,系统而深入地研究内源性有机修饰或外源性有机成分引入对溶胶-凝胶过程的影响对于材料制备、优化有机-无机杂化材料的合成条件、理解最终材料的性能具有重要的理论和应用价值。基于以上思想,本论文主要开展了以此相关的工作,包括以下两部分内容: (1)首次以水为连续相、以长链有机修饰硅氧烷的水解产物形成正相胶束为预想模型,利用荧光探针技术并结合激光光散射等技术研究了五种含有不同有机结构的硅氧烷水解-缩聚反应过程,重点考察了不同有机取代基对产物在溶液中组织方式的影响,以及组织方式对缩合产物物种分布的影响。实验以芘为荧光探针利用静态荧光光谱在线跟踪了具有不同结构特点的有机修饰硅氧烷在酸性条件下的水解和缩聚反应过程,并在体系较为稳定之后进行了荧光猝灭测试。实验结果表明:以芘为探针的荧光光谱信息能从分子尺度上灵敏地反映出不同前驱体水解-缩合产物在溶液中的存在方式以及水解-缩聚过程中物种的演化过程。在含短链有机基团和含有可质子化环氧基前驱体的水解体系中,芘荧光光谱与在背景溶液中得到的荧光光谱类似,猝灭剂对芘的荧光具有较高的猝灭效率。上述荧光光谱行为证明这些体系的水解产物可均匀分散于水相,对荧光探针分子没有明显的增溶作用。当荧光分子芘处于含长链取代基前驱体水解体系中,其发射光谱表现出与其在水体系明显的差异性,具有较强的激基缔合物的荧光发射特征,且猝灭剂的猝灭效率较低。荧光光谱行为证明这些体系的水解产物具有类似表面活性剂的两亲更多还原

【Abstract】 It has been an increasing interest in employing Ormosils (Organically Modified Siloxanes) as precursors to prepare various Organic-Inorganic materials through sol-gel processing. Those materials with chemical inertness, mechanical stability, optical transparency are becoming more and more widely used for optical and electrical materials, chemical/biomedical sensors, catalyst, multifunctional coatings and films, and so forth.Organic component can be introduced in the sol-gel materials by two ways:precursor being organically modified and organic additives being incorporated insol-gels. Different from traditional sol-gel precursors with simple structure and lowermolecular weight, Ormosils present marked substituent effects on sol-gel processdepending on the structure and property of the organic substituent R. In summary, Rgroup has significant influences on reaction rate of hydrolysis-condensation, speciesdistribution of the silonols and silicates, structure evolution and the spatial arrangement,and type of self-organizations. The incorporation of organic additives to sol-gel systemaffects the reaction rate of the precursor undergoing hydrolysis and condensation,modulates the size distribution and dimension of the particles in sol, and controls themorphology of the materials. According to the effects of organic substituent andadditives, the structures and properties of sol-gel materials can be modified,accompanied with the function of composite materials being enlarged. Therefore, it issignificant both in theory and application to systematically investigate the influences ofthe organic moiety on the sol-gel process, which assists in further understanding theorganic modification mechanism in the sol-gel process, controlling the synthesisconditions of organic-inorganic hybrid materials and taking deep insight into propertiesof the final products. With emphasis on the insights above mentioned, we carried out theresearch in this thesis mainly including two parts:(1) For the first time, based on results obtained from fluorescence probe technique and Laser Light Scattering following five hydrolysis-condensation systems derived from different Ormosils with different organic sustituent, the aggregation of hydrolysis products derived from Ormosils with longer substituent into O/W micelle in the aqueous solution was found. The research focuses on organization style of thehydrolysates of Ormosils droved by the organic group with characteristic chemical structure and the effects of such organization style on the evolution of species in condensation process. The in-situ stationary fluorescence spectroscopy with pyrene as a probe was used to follow the hydrolysis and condensation of Ormosils in acid condition. Fluorescence quenching technique was also used to examine the probe behavior in sols. The information obtained from fluorescence spectroscopy shows that at molecular scale, pyrene as a fluorescence’probe could respond sensitively to the organization style and evolution of species produced by Ormosils during the hydrolysis-condensation reaction. When pyrene molecules located in the systems derived from Ormosils with short alkyl group or protonated epoxy group, the fluorescence spectroscopy was similar to that in control solution. It indicates that species of hydrolysates dispersed in the sols and such systems are homogenous, which was also confirmed by obvious fluorescence quenching. In comparison with control solution, when pyrene molecules located in the systems derived from Ormosils with long organic group, a market excimer emission and a decreased fluorescence quenching were observed, implying such systems are inhomogenous. The fluorescence behavior are fitted to the fact that the hydrolysates in these systems are amphiphilic molecules and prone to aggregate like a surfactant to form micelle.Moreover, information from in-situ fluorescence spectra demonstrates that the organization style of the hydrolysates may affect the kinetics of condensation and result in variation of the species. In summary, organic moiety in the precursor with hydrophobicity and steric inhibition restrains the Si—O—Si chain from developing and result in a narrow size distribution of condensation products. Comparatively, a wide distribution of the products in size engenders when the precursor is modified by short hydrophobic group or long hydrophilic group. While oligomers derived from precursor with longer organic chain prefers to precipitate from bulk solution due to strong hydrophobicity.(2) Mechanism on gelation of MAPTMS enhanced by NPG as additives was investigated. A series of techniques including ATR-FT IR, 29SiNMR, *HNMR Raman, UV-Vis, and viscosity have been utilized to follow the sol-gel process of MAPTMS in presence and absence of NPG Moreover, TGA-DSC, XRD, TEM were employed to characterize final solid-state material. Based on the experimental results, the mechanism on the gelation of MAPTMS sol-gel system enhanced by NPG was proposed.hi earlier stage of the reaction for MAPTMS hydrolysis-condensation system, hydrolysate—silanols with long hydrophobic organic tail R=—CH2CH2CH2O(CO)C-(CH3)CH2 and hydrophilic head Si-OH resemble surfactant and aggregate into W/O micelle at high precursor/water ratio. NPG molecule exhibits hydrophobic phenyl and hydrophilic -NH- and -COOH. As a result, a H-bond interaction occurs between Si-OH in hydrolysate and -NH- or -COOH in NPG, hydrophobic interaction and 71-71 stacking between R of hydrolysate and phenyl of NPG make NPG molecules insert aggregates palings formed by silanols and for co-aggregation. An "isolation effect" restrains the condensation between silanols and enhances hydrolysis of Si-OCH3 in the precursor. With increase in surfactant-like silanols, a concentrated microemulsion system engenders. With the reaction going on, decrease in water and increase in methanol lead to abatement of H-bond interaction. Consequently, the microemulsion conformation is destroyed and instead of it, a gel emulsion system with network structure forms. Subsequently, a large number of Si-OH condensate quickly into silicates with high branched and cross-linked structure, and gel emulsions finally transform into solid-state gel.更多还原