| As one of the most important polymer functional composites, electrically conductive polymeric composites(CPCs) have attracted great interest in many applications such as energy storage, batteries, three-dimensional printing materials,electromagnetic shielding, flexible display, and smart sensors. The theory and practice have shown that constructing a continuous and compact network of the conductive fillers in polymeric matrix is essential to prepare composites with high conductivity. It is a conventional method to construct such a network mainly by increasing conductive fillers until the percolation appears. As most polymers have very low electrical conductivity, the electrically conductive fillers are incorporated into polymers to fabricate CPCs. Many efforts have been focused on how to build conductive networks in polymer matrix using electrically conductive fillers with high aspect ratio,including carbon black particles, carbon fiber, graphite flake, carbon nanotubes (CNTs)and graphene.Generally, there are mainly three approaches to obtain a continual conductive network. A widely adopted processing technology is to increase the fraction of the conductive fillers to a certain value until the percolation threshold appears. Another method is to adopt a system of two immiscible polymers and conductive fillers. With suitable fraction ratio of the two polymers and thermodynamic conditions, a co-continuous two-phase structure with selected location of the fillers in one polymer could be obtained, which serves as continuous conductive network. The third method is to form a segregated structure in the composites by compressing a mixture of polymer granules decorated with conductive fillers via dry or solution mixing to construct the segregated conductive networks. In spite of an increase in electrical conductivity at a higher loading of fillers when the self-assembled network was formed, conductivity of the composites improves little as the content of fillers is above the percolation area. On the contrary, it may lead processing performance and mechanical properties fall down sharply. The main reason why electrical conductivity could not further improve is that the average gap of conducting fillers in the network plays a crucial role in all of parameters and conditions affecting the level of conductivity of the composites rather than filler volume faction.In order to further improve electrical conductivities of CPCs, a novel method of Spatial Confining Forced Network Assembly (SCFNA) for preparation of high-performance electrically conductive composites was proposed for reducing the average gap of adjacent fillers in the network. The main idea of SCFNA is introducing a mechanical delivered additional interaction to carry out a forced assembly on loose self-assembly network in spatial confining compression. The exceeded polymer between the fillers at the threads will be squeezed out as forced assembly reaction is much bigger than self-assembly reaction in process of forced compression. In this way,the forced-assembly network is constructed. Because of compact network, the electrical conductivity by Spatial Confining Forced Network Assembly (SCFNA)method can be enhanced. The main work is as follows:1, Thermoset PDMS and thermoplastic PP were represented as two kinds of polymer matrix, PDMS PDMS/SCF and PP/SCF composites were prepared by SCFNA method. Compared with conventional compounding method, the electro-conductive properties of the composites prepared by above SCFNA method can be enhanced up to several times, or even orders of magnitudes. The percolation threshold values of the composites are 0.45wt%, 3.5wt%, respectively. The influence of processing parameters, filler content, compressed thickness and microstructure array on the conductivity of composites was studied. It revealed that the compressed thickness is a crucial factor on the conductivity of composites including filler content,especially at high loading of fillers. The feasibility of the preparation of high performance conductive composites and the performance improvement potential through this method were verified.2, Ternary PDMS electrically conductive composites were prepared by SCFNA method, compared with graphene(G), superconductive carbon black particles(CCB),the combination of multi-walled carbon nanotubes(MWNTs) with short carbon fiber(SCF) was optimal performance on electrical conductivity. At the same time,three components processing mixed sequence significantly affected the electrical conductivity and mechanical properties of composites. Changing the three components of PDMS, CCB, SCF mixed processing sequence, the conductivity of the composite PDMS/SCF/CCB and mechanics performance would make a difference.The conductive performance was optimal when PDMS and CCB were mixed firstly,then SCF was added into their blend. However, the mechanical properties were the optimal when SCF and CCB were mixed firstly, then the mixture of fillers was added into PDMS.3, High electro-conductive polydimethylsiloxane ( PDMS ) /short carbon fiber(SCF) with bolting cloth composites with a low percolation threshold of 0.06wt%were prepared by a Spatial Confining Forced Network Assembly(SCFNA) method.The addition of bolting cloth further improved the electrical conductivity and the mechanical property of the composite sheets. Moreover, if the mesh number of the bolting cloth is large enough, the carbon fibers will be impeded from penetrating the bolting cloth together with the polymer when they are co-compressed, thus an electrically conductive film with single or double insulating face can be prepared through this method. By adding a small amount of nano filler such as superconductive carbon black particles(CCB), graphene(G), surface electrical conductivity of composites can be adjusted. |
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