| Composite conductive foam materials are a class of polymeric porous materials doped with conductive media,which are widely used in pressure sensing,health monitoring,fire warning and other fields for their excellent performance.Silicone rubber（SR）has low volume shrinkage,stable physical and chemical properties,resistance to oil and dirt and aging,and cheap,etc.,can be used as a composite conductive foam matrix material.The conductive media commonly used in silicone matrix are carbon nanotubes,graphene and conductive carbon black（CCB）,due to the surface of these carbon nanoparticles are rich in hydroxyl groups and other functional groups,in the silicone rubber matrix is easy to cause a sharp increase in system viscosity,resulting in foaming difficulties.The common solution is to modify the surface of the particles,which is time-consuming and low yielding and cannot be applied on a large scale.To address this problem,two SR/CCB conductive composite foams with different structures were prepared by the dilution-assisted chemical foaming method with hydrogen-containing silicone oil（PHMS）and the solvated precipitation template-solvation adsorption method,and the properties of these two materials were discussed to investigate the conductive mechanism of CCB in closed-cell and open-cell conductive silicone rubber foams.The main study is divided into two parts as follows:1.In this paper,basic silicone rubber foams（SRF）with closed pore structure and conductive silicone rubber foams（CSRF）were firstly prepared using sodium bicarbonate as the foaming agent and PHMS as the diluent.For SRF,the results showed that the highest porosity（61.93%）was achieved when the foaming agent content was70 phr,the foaming temperature was 200℃,and the foaming time was 20 min,and the good elasticity was maintained after 100 times of 50%compressive strain cycles.The percolation threshold of CSRF material was obtained at 6 phr of CCB addition,and CCB could be added in the system up to 10 phr,when the sample resistance was low and could be stable during 240 h of static storage.At the same time,CSRF-10 has a resistance change of up to 40%at 50%compressive strain.However,the addition of non-volatile hydrogen-containing silicone oil increases the cross-link density of the system and causes a decrease in the flexibility of the material.2.A composite layered silicone rubber foam based on an open-pore structure was developed by the template method,and the SR/CCB mixed layered conductive silicone rubber foam（MLCSRF）was successfully prepared by the swelling-adsorption method to make it conductive.The effects of the number of layers and adsorption amount on the conductivity,sensitivity,and stability performance of MLCSRF under pressure were investigated,and the mechanism of conductivity of adsorbed carbon black in the open-cell foam was discussed.The results show that the decrease in resistance of the material under pressure originates from the close proximity and contact of the adsorbed CCBs on the walls of the bubble pores with each other.When the number of foam layers in the laminar structure is 2,the concentration of conductive dispersion is 1 g/L,and the number of adsorptions is 5 times for 60 min each,the obtained material MLCSRF2-1-5-60 has a resistance change of 39.17%in the pressure range of 0-25 N,and a sensitivity of up to 6.39?10-3 k Pa-1 in the compressive stress range of 0-50 k Pa,and its resistance-mechanical stability performance is excellent,with the rate of change of resistance remaining essentially the same during 100 cycles of 25%compressive strain.Finally,the application of MLCSRF materials in biosensing is explored.The MLCSRF2-1-5-60 material was assembled into a simple sensor and detected human motion.The sensor can produce good response to the motion of several parts of the human body,which indicates that this material has a promising development in pressure sensing and human motion detection. |
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