【作者】 李为；

【导师】 武培怡；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2010， 博士

【摘要】 本论文围绕有机/无机复合物的制备及生长机理研究展开。大自然在制备有机/无机复合物方面为我们作出了很好的榜样：广泛存在于生物体中的生物矿物,就是在有机模板引导下矿物相自组装形成的高度有序的复合材料。因此,我们的研究从体外模拟生物矿化出发,制备了多种生物聚合物/无机盐复合物,并对有机物调控晶体生长的机理进行了探讨。将矿化与工业制备相结合,我们发展了高压/超临界二氧化碳碳酸化法,制备了亚微米级复合物并可通过调节实验条件控制复合物的粒径、形貌,对此我们提出了相应的机理,对体外模拟矿化研究形成了一定的参照。为了深入分析复合物中的有机/无机相互作用,我们采用红外光谱结合二维相关分析,对有机基质的结构进行了深入的研究,并初步探讨了有机质和无机矿物之间的相互作用。论文全文共分为七章。第一章绪论从有机/无机复合材料和自组装过程入题,着重介绍了生物体内矿化以及有机物调控碳酸盐矿化的研究进展,概述了一种较新的工业制备碳酸钙方法-高压/超临界二氧化碳碳酸化法。此外,绪论部分也对我们在研究有机/无机相互作用时采用的主要手段-红外光谱以及二维相关分析做了简单的介绍。在第二章中,我们采用仿生的二氧化碳扩散法,以羧甲基纤维素(以下简称CMC)为基质调控了碳酸钙的结晶过程,制备了CMC/CaCO3复合物。在特定的条件下,我们得到了“玫瑰花”状的CMC/CaCO3复合粒子,由小的方块状晶体单元堆积而成,且粒径分布均匀。通过时间分辨实验对形貌发育过程的跟踪,我们推测了“玫瑰花”状粒子的形成过程,提出了“高分子引导下的无机晶体单元聚集”机理。具体而言,结晶过程中,无定型CaCO3核首先形成,晶体单元在其上堆积、生长。在堆积时,吸附于晶体单元上的高分子链间存在较强的相互排斥作用,使得方块状晶体单元不能完全重合堆积形成斜方六面体状粒子,而只能错开一定面积聚集,最终形成“玫瑰花”状粒子。改变有机质的浓度我们调控得到了不同形貌、结构的复合物,发现调低有机质浓度,球状粒子逐渐过渡成为斜方六面体状,这也进一步证实了上述堆积机理。由于其良好的生物相容性,CMC不仅在实验室被广泛使用,而且是常见的工业原料,因此,这里的研究不仅对生物矿化机理的明晰有一定的贡献,而且也提供了一种在工业上制备具有特定结构、形貌碳酸钙复合粒子的有效方法。第三章中我们继续以CMC为有机基质,调控碳酸钡晶体的生长。首先采用分子动力学模拟的方法对CMC链段和BaCO3晶体单元之间的相互作用进行了分析,结果表明,由于链段和晶格离子之间的静电作用,CMC链段倾向于吸附在针状晶体单元的两端,这为我们探讨晶体聚集机理提供了参考。在低浓度下,我们得到了哑铃状BaCO3复合粒子,通过时间分辨实验,结合分子动力学模拟结果,我们认为：高分子链吸附在BaCO3针状单元的两端,链与链之间的静电排斥作用以及体积占据作用导致针与针聚集时不能平行、紧密地堆积,而必须张开一定角度堆积,这样就形成了针状单元聚集而成的哑铃状碳酸钡复合物。这和第二章对碳酸钙研究所提出的机理是高度一致的。我们进一步改变有机基质浓度,调控得到了花菜状、双球状及球状BaCO3聚集体,实现了聚集体结构和形貌的可调控性。和第二章对比,这一章工作通过对另一种碳酸盐的调控,进一步证实了“高分子引导下的无机晶体单元聚集”机理,而且也提供了一个工业上可行的制备BaCO3晶体的方法。和第二、三章不同,第四章中我们发展了一种新的偏重于工业制备的矿化方法,即采用高压/超临界二氧化碳碳酸化法制备碳酸盐复合物。以CMC为模板在水溶液中能够得到几百纳米的椭球状方解石粒子,而这种复合粒子通过传统的矿化方法是难以得到的。通过调节实验条件,包括有机物浓度、分子量、二氧化碳的温度和压力等,我们可以有效地调控所得复合物的粒径和形貌。而且,通过和聚丙烯酸的调控结果对比,我们得出,所得粒子形貌和所采用高分子的链的柔顺性密切相关,简单来说就是：偏柔性高分子链引导形成球状粒子,偏刚性链引导形成椭球状粒子。综合以上实验结果,我们提出了在高分子链引导下高压/超临界二氧化碳碳酸化法制备碳酸钙复合物过程中的“直接模板”机理。我们认为,在该方法中,矿化速度很快,体系相对均匀,离子吸附在高分子链上并直接以之为模板成核、生长,并将高分子模板包裹其中形成复合物。由此,我们可以通过改变有机质浓度和分子量来实现对复合物粒径、形貌的有效调控。与体外模拟矿化的方法相比,第四章提供的高压/超临界二氧化碳碳酸化法矿化速度较快,偏向于工业制备,但是也可以对生物矿化机理形成一定的启发。更重要的是,这种方法将工业固定二氧化碳和复合粒子制备结合在一起,提供了很大的想象空间。我们用这种方法进行了碳酸钡复合粒子制备的尝试,得到了直径几百纳米的纤维状碳酸钡,值得关注。为了研究复合物中有机/无机相互作用,我们首先对所采用的有机基质的结构进行了细致、深入的分析。第五章主要采用红外光谱方法结合二维相关分析对CMC在40-220℃温度区间的结构特别是氢键结构的变化进行了分析,并明确了常温下CMC中的氢键结构。在CMC升温过程中,有两个重要的温度点：100℃和170℃,前者是CMC中结合水全部逃逸出体系时对应的温度,后者是CMC中未被取代的C6H6开始被氧化的温度。以这两个温度点为界,我们将整个温度区间划分为三段分别进行二维处理。结果表明,在100℃以下,随着温度升高,水分子逃离体系,水合的C=O基团逐渐变为非水合；温度升到100℃以上,链内氢键逐步转变为弱氢键；当温度上升到170℃以上时,未被取代的C6H6基团逐渐被氧化,其与羧甲基之间形成的链间氢键逐渐解离。这一部分的研究对CMC的结构及其工业应用提供了参考,同时也为我们研究CMC-CaCO3复合物中的有机无机相互作用打下了基础。在第五章后面部分,我们对复合物进行了升温红外光谱实验,并简单地讨论了这种相互作用。第六章中采用和研究CMC相似的方法对再生丝蛋白(RSF)膜的结构进行了分析。丝蛋白作为一种常见蛋白,在实验室中被用于组织工程、药物缓释等领域的研究,另一方面,我们课题组之前进行了高压/超临界环境下丝蛋白引导碳酸钙矿化的实验,所以第六章的工作也是在为研究RSF-CaCO3相互作用打基础。我们应用二维相关红外光谱研究了RSF和水之间的相互作用以及升温过程中丝蛋白结构的变化。另外,我们还在超临界二氧化碳环境中,用红外光谱原位监测了RSF膜中结构的变化过程,初步研究了CO2-RSF的相互作用。相信这里的研究将对丝蛋白的应用起到一定的指导作用。第七章对全文的研究工作进行了总结。在多糖及其衍生物引导矿化制备复合物方面,我们推测,阴离子型多糖及其衍生物的链构象偏刚性、且负电荷密度较高导致链与链之间的相互排斥作用较强,因此有机质除了在晶体成核、初期生长过程中起到调控作用之外,在后期对晶体单元聚集过程的影响也很明显。文末提出了论文的未竟之处及有待解决的问题。更多还原

【Abstract】 Inspired by the mineralization in biological organisms, the fabrication of higher ordered inorganic crystals induced by polymer chains has received much attention. In this thesis, we used several biopolymers to induce the fabrication of different inorganic salts with different methods, and suggested the corresponding reaction mechanism, further explored the organic-inorganic interaction in the composites. We adopted biomimetic CO2 diffusion method to synthesize carbonates and obtained rosette-like CaCO3 particles and various morphologies of BaCO3 aggregates. Furthermore, we developed a new method using polymers as templates via carbonation route with compressed/supercritical CO2 and obtained submicronic CaCO3 particles with ellipsoidal morphology in aqueous solution, which were rarely fabricated with traditional mineralization methods. To deeply investigate the organic-inorganic interaction in the composites, we introduced infrared spectroscopic method in combination with two dimensional correlation analysis to examine the products, before which the structure of the organic templates was carefully studied.Carboxymethyl cellulose (CMC), widely used in many industrial aspects and also in laboratory due to its good biocompatibility, was systematically investigated in regulating the CaCO3 crystallization using CO2 diffusion method in ChapterⅡ. Rosette-like calcite spherules in uniform size with their surfaces composed of rhombohedral subunits were synthesized in a certain experimental condition. The evolution of the composite morphologies was traced by time-resolved experiments and the possible route in which rosette-like spherules formed was proposed. We suggested that amorphous calcium carbonate precursor formed initially and acted as secondary nuclei, followed by the stacking of rhombohedral subunits in partial rather than complete superposition between each other due to the electrostatic repulsive interactions between the polyanion chains adsorbed on the blocks, which resulted in rosette-like morphology. Mineralization experiments in CMC solutions with different concentrations were also carried out and the results obtained at no higher than 1g/L further proved the above "polymer-induced crystalline units self-assembly" mechanism from the fact that the extent of the polymer influence decreased proportionally with the concentration, i.e. degree of superposition of the building blocks became larger by decreasing the CMC concentration. This work not only provided for the formation mechanisms of the rosette-like calcite spherules but also leaded to a new route to fabricate new composites which can be used in many industrial aspects.In ChapterⅢ, we continued to utilize CMC as template to mediate the nucleation and growth of BaCO3. First we calculated the interaction between CMC chains and crystalline needle-like units of BaCO3 by molecular dynamic simulation, concluding that the (111) face of crystalline units is the most favorable face for CMC chains to attach onto. Based on the simulation results and the time-resolved experiments, we suggested the possible route in which dumbbell-like BaCO3 aggregates formed, that is, through the process of polymer induced stacking of needle-like units. Moreover, we realized the control over the morphology of aggregates from dumbbell-like to spherical particles by simply adjusting the polymer concentration. The results here further proved that the "polymer induced crystalline units self-assembly" mechanism was reasonable. By clarifying the aggregation mechanism mediated by polymer chains, we demonstrated a simple method to fabricate BaCO3 particles with controllable morphologies.In ChapterⅣ, instead of traditional mineralization method, we developed a new carbonation route, with compressed/supercritical CO2, to fabricate composites. Submicronic CaCO3 particles with ellipsoidal morphology were synthesized taking CMC as template. By regulating some experimental parameters, like the concentration and molecular weight of CMC, as well as the CO2 pressure and temperature, the morphology and size of the CaCO3 particles could be effectively controlled. Besides, in contrast to the effective results of another additive, Polyacrylic Acid (PAA), we suggested that the morphology of the synthesized particles was strongly related to the flexibility of the polymer chains, namely, the relatively rigid chains induced the formation of ellipsoidal particles while the more flexible chains would result in the spherical ones. We further discussed the mineralization mechanism by this carbonation route:the polymer chains served as the "direct skeletons" and the ions attached along the chains to realize the nucleation and growth. The morphology of CaCO3 aggregates was tailored by the flexibility of the polymer chain, while the size of the particles was related with the chain length of the polymer. In comparison with the traditional mineralization methods, we provided a highly efficient and versatile approach to integrate the fixation of CO2 and the regulating effect of different polymer chains, to produce submicroscopic CaCO3 particles and further control their morphologies and sizes.To deeply investigate the organic-inorganic interaction, we carefully examined the structure of CMC in ChapterⅤ. We demonstrated a full view of infrared spectroscopic results in the temperature range of 40-220℃, mainly aiming at the hydrogen bonds in CMC. The two important transition points were defined, i.e., 100℃corresponding to the complete loss of water molecules and 170℃to the starting temperature point the O6H6 groups being oxidized. The series of IR spectra during heating from 40-220℃was analyzed by the two-dimensional correlation method. With the evaporating of water molecules, the hydrated C=O groups gradually transited into non-hydrated C=O groups. As the temperature continued to increase, the intrachain hydrogen bonds were weakened and transited into weak hydrogen bonds. When the temperature was higher than 170℃, the O6H6 groups were gradually oxidized and thus the interchain hydrogen bonds formed between CH2COONa groups and O6H6 were weakened. In summary, we defined the main sorts of hydrogen bonds in CMC and pictured the changes of the hydrogen bonds structure during heating process, which may provide for the application in both industry aspects and laboratory use and also set a foundation for the researches on the CMC-CaCO3 interaction in composites. The interaction was primarily discussed in ChapterⅤ.In Chapter VI, the structure of regenerated silk fibroin (RSF) was studied using the similar method with that in CMC. RSF was used to mediate the crystallization of CaCO3 with compressed/supercritical CO2 carbonation route by our research group, and our research here also tended to set a foundation for the analysis of the organic-inorganic interaction. We defined several interactions between RSF and water molecules, as well as the variation of the structures with temperature. Besides, we investigated the CO2-RSF interaction with in situ temperature-dependent infrared in supercritical CO2 environment, which may also serve to the application of silk fibers in different industrial areas.Chapter VII is the summary of the thesis. We compared the different mineralization methods, summarized the "polymer induced crystalline units self-assembly" mechanism with traditional CO2 diffusion method and "direct templates" mechanism in compressed/supercritical CO2 carbonation route. Questions waiting to be addressed were also proposed.更多还原