| 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.
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