摘要
利用有机修饰硅氧烷作为前驱体经由溶胶-凝胶过程制备各种各样的有机-无机杂化材料成为近年来的研究热点。由于这些杂化材料具有化学稳定、光学透明、机械性能优越等特点,因而被广泛应用于光学器件、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。因此,系统而深入地研究有机修饰成分引入对溶胶-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,本论文主要开展了与此相关的工作,包括以下两部分内容:
(1)以甲基丙烯酰氧丙基三甲氧基硅烷(MAPTMS)为前驱体,利用荧光光谱、在线衰减全反射红外光谱(In-situ ATR-FT-IR),比较性地研究了在本体及气液界面条件下MAPTMS在酸性介质中的水解-缩合过程。借助于LB膜技术,测定了MAPTMS在气液界面水解-缩合反应过程中的π-A曲线。不论在本体相还是气液界面相,荧光探针芘均表现出明显的芘分子完全重叠及部分重叠的激基缔合物的荧光发射特征。结果表明:MAPTMS水解产物在水相中发生簇集,而且簇集体疏水端相互作用存在一定刚性。随反应进行芘的荧光光谱均表现出明显的涨落,但本体相荧光光谱变化较气液界面相剧烈。ATR-FT-IR光谱在线检测表明:本体水解缩合产物具有较高的聚合度,而气液界面水解缩合产物聚合度较低。说明体系中存在可逆性簇集与解簇集行为,且在气液界面MAPTMS水解产物受限程度比本体相大。分子在气液界面上的聚集行为也由π-A曲线的结果得到进一步证实。文中依据MAPTMS水解产物具有类似表面活性剂的特性对上述实验结果给予解释。
(2)以3-缩水甘油醚丙基三甲氧基硅烷(GPTMS)为前驱体,利用荧光光谱、在线衰减全反射红外光谱(In-situ ATR-FT-IR),比较性地研究了在本体及气液界面条件下GFTMS在酸性介质中的水解-缩合过程。借助于LB膜技术,测定了GPTMS在气液界面水解-缩合反应过程中的π-A曲线。结果表明,反应初期,无论对于本体相还是气液界面相应荧光探针分子均没有出现激基缔合物的荧光发射特征,反映了GPTMS水解产物在水相中均匀分散,没有表现出簇集行为和类似表面活性剂的双亲性。但随反应进行,出现了420 nm处的激基缔合物峰,说明部分缩合产物簇集于气液界面。π-A曲线所表现出的特征也证明了水解产物在气液界面上具有一定的双亲性。荧光光谱结合ATR-FT-IR光谱对GPTMS水解-缩合体系本体相与气液界面反应条件下的在线光谱特征表明:反应初期,本体相与气液界面反应条件下的反应变化趋势相近,GPTMS分子中存在环氧基可被质子化,故水解产物为分子两端均为极性基团,水解产物具有较高的水溶性,水解产物单分散在溶液中,相互发生缩聚反应较慢。不同于本体样,随反应进行气液界面样出现部分缩合产物的簇集,表现出一定的双亲性。上述结果对以GPTMS为前驱体可控性制备无机-有机杂化材料及材料表面修饰均具有重要的参考价值。
It has been an increasing interest in employing Ormosils(Organically Modified Siloxanes) as precursors to prepare various Organic-Inorganic materials through sol-gel processe.These materials with chemical inertness,mechanical stability,optical transparency are becoming more and more widely used in optical and electrical materials,chemical biomedical sensors,catalyst, multifunctional coatings and films,and so forth.
Organic component can be introduced into the sol-gel materials by two ways:precursor being organically modified and organic additives being incorporated in sol-gels.Being different from traditional sol-gel precursors with simple structure and lower molecular weight,Ormosils present the marked substituent effects on sol-gel process depending on the structure and property of the organic substituent R.In summary,R group has significant influences on reaction rate of hydrolysis and condensation,species distribution of the silanols and silicates,and type of self-organizations. Therefore,it is significant both in theory and application to systematically investigate the influences of the organic moiety on the sol-gel process,which assists in further understanding the organic modification mechanism in the sol-gel process,controlling the synthesis conditions of organicinorganic hybrid materials and taking deep insight into properties of the final products.With emphasis on the insights above mentioned,we carried out the research in this thesis mainly including two parts:
(1) The aggregation behavior occurred in bulk phase and at air-water interface during hydrolysis and condensation processe of 3-methacryloxypropyltrimethoxysilane(MAPTMS) were comparatively investigated.The fluorescence spectra of pyrene probing the bulk phase and air-water interface for hydrolysis-condensation process of MAPTMS implied that there were aggregation of hydrolyzates in bulk phase and at air-water interface.Additionally,the variations in fluorescence spectra with time manifested that both hydrolysis and condensation occurred in bulk phase were faster than that at air-water interface.These conclusions were coincident with the results derived from In-situ ATR-FT-IR andπ-A isotherm measurement.The fluctuations in the emission intensity of pyrene were also observed for both cases of bulk phase and air-water interface,indicating that the aggregates were reversible and the fluctuation was more violent in bulk phase than at air-water interface.All findings related to the aggregation could be interpreted in terms of the hydrolyzed MAPTMS being similar to amphiphilic molecule and differences in the fluorescence spectra and IR spectra originating from the bulk phase and air-water interface could be attributed to the difference in the degree of molecular confinement in two cases which makes the hydrolysis and condensation of MAPTMS different.
(2) The hydrolysis-condensation processes of 3-Glycidoxypropyltrimethoxysilane(GPTMS) in bulk phase and air-water interface were followed by means of fluorescent spectroscopy with pyrene as fluorescent probe and In-situ ATR-FT-IR.Additionally,theπ-A curve of the hydrolyzates of GPTMS LB film using the hydrochloric acid solution as the subphase was examined by the KSV Minitrough.In earlier stage of the reaction for GPTMS hydrolysis-condensation system,the fluorescence spectra of pyrene probing the bulk phase and air-water interface implied that there were not aggregations of hydrolyzates in bulk phase and at air-water interface.It indicates that species of hydrolysates dispersed in the solution and such systems are homogenous.Owing to the protonated expoxyl group of GPTMS,the silanols produced from GPTMS do not easily form aggregates because of the presence of two polar ends in the silanols.With the reaction,the spectra of pyrene appear distorted excimer emission at air-water interface,which was also confirmed byπ-A isotherm measurement.The spectroscopic results revealed that the condensation products are prone to form aggregates at air-water interface.That is to say,condensation products at air-water interface are similar to amphiphilic molecule.So all these results are very significant in the controllable preparation of a controlled material and surface modification.
引文
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