Study On The Structure And Properties Of Double Percolation Polymer Conductive Composites

Conductive polymer composites(CPCs)are a type of composites that filling conductive particles into an insulated polymer matrix,which endows the materials electrical conductivity.CPCs have received intensively academic and industrial attentions for several decades due to their good processability,tunable electrical properties,and wide ranges of applications.However,in order to achieve the insulator/conductor transition,very high loadings of conductive fillers are usually needed to add into the insulating polymer matrix,leading to the complex processing,poor mechanical properties,and high cost of the materials.Therefore,how to prepare CPCs with ultra-low electrical percolation threshold has become a recent hot issue.If conductive fillers are introduced into an immiscible polymer blend with co-continuous structure,the percolation threshold could be decreased effectively through the double percolation mechanism.However,it is clear that the mechanical properties of these types of CPCs are normally inferior because of the weak interfacial interactions between the immiscible polymer blends.Therefore,this paper mainly focuses on how to reduce the conductive percolation threshold of CPCs and improve the mechanical properties of CPCs.The main results obtained in this work are listed as follows:1.In this paper,a simple and efficient thermodynamic method is proposed to precisely control multi-walled carbon nanotubes(MWCNTs)at the interface of a co-continuous PS/PMMA blend to design conductive polymer composites with ultralow percolation threshold.The achievement of the interfacial distribution of MWCNTs is attributed to the balance of ?-? interaction between PS and MWCNT surfaces and dipole-dipole interaction between PMMA and carboxyl groups on MWCNT surfaces.It is found that MWCNTs can be well controlled at PS/PMMA interface when carboxyl content on MWCNT surfaces is ca.0.73 wt%,which can exactly make a balance between ?-? interaction and dipole-dipole interaction.Because all the MWCNTs are precisely controlled at the continuous interface to build a percolated conductive pathway,the percolation threshold of this type of conductive polymer composite is lowered from 1.81 wt%(MWCNTs/PS)or 1.46 wt%(MWCNTs/PMMA)to 0.017 wt%,which is an ultralow percolation threshold so far.2.The CPCs of carbon black(CB)/PS/polypropylene(PP)(PS/PP=60 w/40 w)with the percolation threshold of 1.45 wt% is prepared by use of double percolation mechanism.It is clear that the mechanical properties of CB/PS/PP(60 w/40 w)are normally inferior because of the weak interfacial interactions between the immiscible PS/PP blend.Although the mechanical properties of the CPCs are significantly improved after the addition of SEBS,the electrical conductivity shows a remarkable decline when SEBS content is higher than 3 wt%.This is because that the addition of compatibilizer(SEBS)into a co-continuous immiscible polymer blend will reduce the sizes of the phase domains,thereby causing a damage of phase continuity of the double percolation structure.However,it is found that the excellent electrical properties can be still superior because of the maintaining of the double percolation structure and the mechanical properties can also be significantly improved when SEBS content is 2 wt%,which can well balance the electrical properties and mechanical properties for the CPCs containing a double percolation structure.