Preparation Of Polymer Nanocomposites With Ultralow Percolation Threshold Via Electrostatic Interaction Process And Study Of Their Thermal/Electrical Properties

Preparation of polymer nanocomposites with ultralow percolation threshold is the main purpose of most of the researches.The preparation methods of polymer nanocomposites include melt,solution and emulsion blending process.Nanofillers with high specific surface area tend to agglomerate in polymer matrix,which will result in higher viscosity and higher percolation threshold during the melt blending process.Compared to the solution mixing process,no toxic organic solvent is required in the emulsion blending process,which is more environmental friendly.Moreover,the nanofillers can only attach onto the surface the micelles rather than penetrate into the latex particles,which enhances the size exclusion effects of the polymer matrix in the final composites and results in a relatively lower percolation threshold.Firstly,polystyrene（PS）latex was first prepared by using hexadecyl trimethyl ammonium bromide（CTAB）as a cationic surfactant,which created positive charges on the surface of the PS micelles.An in situ demulsification process was then conducted by adding negatively charged graphene oxide（GO）particles into the positively charged PS latex.Thus,GO sheets were attached spontaneously to the surfaces of PS particles through electrostatic adsorption.Followed by in situ reduction and hot pressing,the agglomeration of graphene nanosheets（GN）was largely prohibited by the PS microspheres and facilitated the formation of GN networks in the PS matrix.The obtained PS/GN nanocomposites exhibited excellent electrical properties with a percolation threshold as low as 0.054 vol.%GN.When the GN content reached 1.53 vol.%,the electrical conductivity was 46.32 S/m and the thermal conductivity was 0.47 W/（m·K）.Secondly,the flaky inorganic nanofiller inserted in the complete carbon-based nanofiller conductive network,which cut off the original percolation network to achieve the effect of thermal insulation.Polystyrene（PS）latex was first prepared by using sodium dodecyl sulfate（SDS）as an anionic surfactant,which created negative charges on the surface of the PS micelles.Poly dimethyl diallyl ammonium chloride（PDDA）coated on the outside of the carbon nanotubes（CNT）and the dopamine coated on the surface of the boron nitride（BN）after ultrasonic stripping to bring the surface with positive charges and negative charges,respectively.The positively charged PDDA/CNT adsorbs onto the surface of PS microspheres under electrostatic interaction to form positively charged PS/CNT composite particles.The presence of PS effectively prevented the agglomeration of CNT,and CNT formed interpenetrating network structures in the gaps of PS particles.The negatively charged PDA/BN and the positively charged PS/CNT were incorporated under electrostatic adsorption to construct“sandwich”composite particles,and the BN were aligned in the matrix of PS/CNT.After hot press molding,the orientation structure of BN cut off the complete network structure formed by CNT in PS matrix.CNT and BN in the PS matrix to form a number of local hybrid networks,while the local network of CNT could still effectively transfer heat between BN layers.The obtained PS/CNT/BN nanocomposites exhibited excellent thermal properties,when the CNT content reached 6.5 wt%and BN content reached 20 wt%,the thermal conductivity was 2.301W/（m·K）and the electrical conductivity was less than 10^-6 S/m.