Preparation And Mechanism Of Biomimetic Hierarchical Structure Of Silica Based Carbonate

The complex aesthetic super-hierarchical structure formed by biomineralization and artificial self-assembly is fascinating and amazing,which leads scientists to try to find out its formation law and mechanism.It is of great scientific significance to provide theoretical basis and guidance for the artificial free design and preparation of functional materials of multiscale hierarchical architecture.Currently,the research on self-assembly is limited to the qualitative or empirical adjustment of experimental processes to control the growth pattern and sculpture of self-assembled material system,which lacks of quantitative theoretical framework to accurately characterize and regulate the hierarchical architecture.In preparation and synthesis of hierarchical structures,it is both emerging and challenging to analyze the effects of multiple environmental factors,modulate different functions of the materials and synthesize new superstructures.In order to explore the mechanism of self-assembled hierarchical structure and discover new ultrastructures,silicon-based carbonate system of diverse structure was an ideal model,this system can produce typical tree-like,bottle-like and screw-like biomimetic hierarchical architectures.Due to the complex structure of silicic acid macromolecule,the self-assembly of carbonate system was studied in order to simplify the model.Firstly,the mechanism of self-assembly of the hierarchical carbonate structure is investigated in this thesis.The influence of defects on the growth direction was systematically evaluated by the surface diffusion theory,first-principles calculation and crystallographic analysis.Based on these,we propose a possible mechanism for the formation of nanocrystals building blocks from self-assembly.Furthermore,we characterized the growth of barium carbonate and silica-strontium carbonate at different crystal types on account of supersaturation and lattice mismatch.Secondly,an integrated phenomenological geometric growth model of biomimetic hierarchical structure was established.The nucleation and growth rate of silicon-based carbonates were obtained from the experimental data,and the growth boundary parameters were summarized and determined.The integrated phenomenological growth models of three typical shapes(flat,flower,and spiral)were found,the growth trajectory and rate of silica carbonate hierarchical shape are also quantified,and the model is further verified by numerical simulation,which provides the theoretical basis for the synthesis of biomimetic hierarchical structure and the prediction of the potential new structure.Thirdly,we analyze the effects of organic-inorganic addition on the superstructures,which put forward the related mechanism model.We also found a variety of new controllable biomimetic structures.The introduction of inorganic metal cations,organic cations and polymers to change the chemical environment of aqueous solutions can significantly interfere with the crystallization,precipitation kinetics and crystal morphology of carbonate minerals.The mechanism was extended to explain the multi-factor synergistic effect on inhibiting or promoting carbonate nucleation and growth.Finally,based the above-mentioned investigation and mechanism of the system,we established the method to construct three-phase interface local microenvironment using microfluidic technology;meanwhile,the structure,controllable size and definite growth direction of the self-assembled hierarchical arrays can be controlled by adjusting p H,solution concentration,temperature and CO₂ concentration.The arrayed surface of hierarchical superstructure exhibit superhydrophobility which resists UV,humidity and acid-base;and the superhydrophobility and adjustable adhesion are closely related to the number of arms and the distance between branches.In summary,based on both theoretical and experiment studies of the mechanism of the self-assembly of silicon-based carbonate biomimetic hierarchical structure,a comprehensive model of the self-assembled hierarchical structure of this system has been proposed.In addition,the analysis method of the inherent influence mechanism was established.Finally,this research discovered new structure with well control by employing its law,which provides new ideas and methods for other systemic self-assembling hierarchies beyond silicon-based carbonate.