Preparation And Characterization Of Ordered Inorganic-organic Bio-nacre Composites

Through thousands of years of natural selection,many organisms have evolved unique microstructures with superior properties on them to help them survive better in nature.Nacre is composed of 95%calcium carbonate and 5%organic protein with a"brick and mud"structure.The exquisite microstructure endows itself with extremely toughness.Therefore,after mastering the toughening mechanism of this structure,scholars have used various methods and different materials to prepare bio-nacre materials.In this thesis,bio-materials which are similar to natural nacre in structure and material were prepared by"freeze-mineralization"method,which proved the effectiveness of this method in preparing bio-materials.Through testing its properties,it is found that the bio-nacre material has a relatively large leakage current,so it is difficult to have the electrical properties comparable to the natural nacre.However,the material shows obvious anisotropy,and the thermal conductivity in the in-plane direction reaches 1.15 W/(m·K),which is 2.25 times that in the through-plane direction.The mechanics performance of bio-nacre material is similar to natural nacre,the ultimate stress in the three point bending test is 51.4 Mpa.Its internal complex toughening mechanism,including the mechanism of crack extension and organic bridging mechanism is the fundamental reason for the high mechanical properties of the sample,By imitating the microstructure of the nacre,a new composite material with high toughness can be prepared.Because the"freeze-mineralization"method has shortcomings such as a long preparation cycle,we have also explored and studied other methods of preparing bio-materials.As an effective means to control the internal microstructure of materials,the electric field orientation method is mostly used in the orientation of one-dimensional materials.Here,we use the method of electric field orientation to place a strong electrostatic field on both sides of the suspension in which the micro(nano)plates are mixed with the organic solution,and the suspended micro(nano)plates that slowly settle down are polarized by the electrostatic field,turn it over to achieve the purpose of orientation.The experimental results show that the electric field orientation can effectively control the orientation of the micro(nano)plates in the suspension.Observing the SEM image of the cross-section of the sample,it is found that the microstructure is similar to that of the natural nacre.Next,we use the method of electric field orientation to combine nanoplates of different thicknesses with different organics to prepare different bio-nacre materials to explore the effect of nanosheet thickness and different organics on performance.The results show that the microstructure of the composite material prepared by using thinner nanosheets is more compact,the dielectric constant at low frequency(1 k Hz)is 1.37±0.23 times of the latter,and the thermal conductivity is 1.03±0.02 times of the latter,the maximum The stress is1.08±0.05 times of the latter.The properties of composite materials prepared by using polyethylene oxide(PEO)and polyvinyl alcohol(PVA)are similar.When PANI is mixed with polyaniline(PANI),the properties change significantly.More,the more obvious the change.When W_PANI:W_PVA=1:2,the dielectric constant of the material at low frequency(1k Hz)is increased from 10.99 to 72.49,and the thermal conductivity in the inter-plane direction at room temperature is increased from 1.33 W/(m·K)to 1.65 W/(m·K).However,the addition of polyaniline greatly reduces the ultimate stress and fracture strain of the material.The ultimate stress is reduced from 47.58 MPa to 8.28 MPa,and the fracture strain is also reduced from 0.34%to 0.08%.This article illustrates the effectiveness of using the electric field orientation method to control the orientation of two-dimensional materials,which is of great help to the study of bio-nacre materials.