Conductive Polymer Foams Prepared With Low Loading Of Multi-walled Carbon Nanotubes

Conductive polymer composites which consist of single or hybrid conductive fillers have aroused a great deal of interest due to their widespread applications in anti-static materials, sensor, electromagnetic interference shieldingand so on. Even so, there is still a challenge in preparing high performance conductive foams. At present, two major concerns in this field are to reduce the percolation threshold and achieve high conductivity.However, due to most of the host polymers usedare insulators, the existence of non-conducting polymer within conductive fillers junctions hinders the improvement of electrical conductivity. Therefore, it was indicated that the presence of a conductive polymer between adjacent fillers may greatly reduce the non-contact resistivity.What’s more, the introduction of porous structure into polymer matrix is also an effective way to construct 3D conductive network, which can not only reduce the density of composites but also act as "excluded volume" and templates to direct selective location of fillers.In this article, we report a comprehensive study of electrical conductivity in PS-based MWCNTs-containing poly-HIPE. Different from the conventional concentrated emulsion-based route, we use a surfactant-like conductive polymer latex PEDOT:PSS to disperse CNTs. An important discovery from our experiment is that the combination of conductive polymer particles and CNTs result in synergetic percolation threshold and high volume electrical conductivity.Firstly, the effect of the MWCNTs and their introduced phase on the morphologies of porous PS was discussed. The results show that the nanocomposite prepared by introducing MWCNTs through dispersed phase possessed better conductivity, smaller pore size and uniform size distribution.A control series of foams, prepared by introducing PEDOT:PSS into concentrate emulsions, was investigated to determine the effect of PEDOT:PSS on composite foams and at what ratio of MWCNTs/PEDOT:PSS the foam reaches a relatively high electrical conductivity. As a result, the incorporation of PEDOT:PSS can improve the conductivity markedly and when the ratio of 1:4 of MWCNTs to PEDOT:PSS are required for good conductivity.The effect of PEDOT:PSS/MWCNTs on the porous morphology, electrical conductivity and mechanical properties of materials were characterized by TEM, SEM, electrometer and electronic universal testing machine. It was obvious that mixing conductive fillers of different size and shapes can lead to synergetic effect which can form co-supporting conductive network. Moreover, the porous structure of polymer foams can direct the selective location of fillers in the cell walls and cell struts that can strongly reduce the percolation threshold. In addition, the highest conductivity was achieved by the foam structure with fine porous morphology, thin pore wall, and appropriate additive amount of nanofillers.