Research On Fabrication And Properties Of Electrically Conductive Inorganic/polymer Hybrids

Conductive polymer composite?CPC?is one of the most important functional electronic materials which can be used to connect the electronic parts and components,and also to realize and improve the portability and flexibility of the electric devices.With development of the electric devices toward high integration,multi-functionalization,portable and flexible,higher and higher performance of the electronic materials such as electrically conductive materials are required.In view of the existing problems of the CPCs such as complex fabrication process,high cost,difficult to meet the large-scale printing technology for the industry production and lack of mechanical flexibility,a new type of CPC was designed and fabricated.Polystyrene?PS?microspheres were used as core,silver nanoparticles,graphene or silver nanowires acted as conductive elements to construct a three dimensional conductive network,which can effectively decrease the usage amount and the percolation threshold of the CPCs,and also maintain high electrical conductivity.Moreover,the core-shell structured hybrids of the PS microspheres and conductive elements can reduce the density of the conductive fillers compared to the pure silver fillers,and also alleviate the phenomenon of sedimentation and delamination of the conductive paste.A series of conductive hybrids faced various applications were fabricated by controlled the design of size and size distribution and functional groups.The as-prepared inorganic/polymer conductive hybrids achieved the balance of their comprehensive performance about printability,highly electrical conductivity,high sensitivity and wide strain work range,and have promising application potential and value in flexible and wearable electronics such as anisotropic conductive adhesives/films?ACAs/ACFs?,flexible printed circuit boards?FPCBs?,flexible conductor,flexible strain sensors and so on.The main work is summarized as follows:1.The preparation and properties of the micron sized monodisperse polystyrene/silver hybrid microspheres.Monodisperse polystyrene microspheres?PS?with diameter of 5.6?m were synthesized via dispersion polymerization method,and silver nanoparticles?AgNPs?were subsequently uniformly deposited onto the surface of the PS microspheres by electroless plating.The size,size distribution and loading amount of AgNPs on PS surfaces are tuned through the conditions such as the sulfonation reaction,Sn²⁺ions sensitized reaction and the concentration of silver ammonia solution,and further control the electrical conductivity of the PS/Ag hybrid microspheres.When the average size is⁶0 nm and loading is 60.77 wt%of the AgNPs,the PS/Ag hybrid microspheres possess a continuous,complete and compact AgNPs layer,and show a highly electrical conductivity of 3.33×10⁵ S m^-1.Due to the high conductivity,uniform and suitable size of the PS/Ag hybrid microspheres,they have promising application potential in anisotropic conductive adhesives/films?ACAs/ACFs?for conductive interconnection of fine pitch flip chip packages.2.The preparation and properties of the monodisperse polystyrene/silver hybrid nanospheres.A series of different sized monodisperse polystyrene nanospheres?250⁴10 nm,CV<5%?with carboxyl groups?-COOH?were prepared by soap-free emulsion polymerization,and the polystyrene/silver hybrid nanospheres were fabricated via in-situ chemical reduction.The existence of the surface-COOH groups make easy of the AgNPs uniformly deposited on the surface of PS nanospheres,and the size and coverage density of AgNPs on PS nanospheres were controlled by the-COOH amount and concentration of silver ammonia solution.The PS/Ag hybrid nanospheres exhibit good surface enhanced Raman scattering?SERS?properties with low detection limit of 10^-10 M and high enhancement factor?EF?of 2.71×10⁷ for 4-ABT probe molecules.The PS/Ag hybrid nanospheres with 46 wt%AgNPs loading were successfully used to formulate conductive ink and then printed onto polyimide?PI?films to fabricate conductive patterns.The printed patterns show a low resistivity of 2.45×10^-5?·cm after sintering under 150?for 2 h.3.The fabrication and properties of the printable polystyrene/silver/PDMS flexible conductive hybrids.The polydisperse polystyrene/silver hybrid conductive microspheres with average size of 5.68?m ranging 2¹1?m were prepared via modified electroless plating and used as conductive fillers.PS@Ag/PDMS flexible conductive hybrids were fabricated by mixing the PS@Ag fillers with liquid PDMS and its curing agent followed by heating solidify.The PS@Ag/PDMS conductive composites exhibit high conductive conductivity of 4.12×10⁴ S m^-1at a low actual silver loading of 42.8 wt%,and demonstrate excellent mechanical flexibility such as stretching,bending and torsion,and also electrical stability under mechanical deformations.Moreover,the paste of PS@Ag/PDMS can be printed on various substrates such as textile,paper,polymer film and glass,revealing excellent printing adaptability.The optimum resolution of the printed patterns is 100?m/100?m?line width/line spacing?,which shows a similar level compared with traditional silver conductive adhesives,suggesting excellent application prospect.4.The fabrication and properties of polystyrene/silver/PDMS flexible strain sensors.The electrical conductivity,mechanical properties,cyclic stability and sensitivity of the PS@Ag/PDMS conductive composites were investigated on the basis of the research of the previous chapter.The PS@Ag/PDMS conductive composites show a low percolation of 3.5vol%or 26.9 wt%of actual silver,implying fewer silver filler is required to achieve the special conductivity and also reduce the cost of the composites.Furthermore,the PS@Ag/PDMS samples exhibit excellent long-term electrical stability after accelerated aging under 85?&85%RH conditions for 1750 h.The electrical conductivity,elongation at break and resistance-strain sensitivity of the PS@Ag/PDMS conductive composites can be tuned by controlling the PS@Ag filler loading.The PS@Ag/PDMS conductive composites with high filler loading show a high conductivity but relatively low elongation and sensitivity.However,there is high elongation and sensitivity but low conductivity for the PS@Ag/PDMS with a low loading of filler.It is important to choose suitable PS@Ag filler loading to achieve good comprehensive.For example,the PS@Ag/PDMS with 60 wt%filler exhibit excellent printability and high conductivity of 1.65×10⁴ S m^-1,also high sensitivity of 17.5,6.0 and 78.6at strain of 0%¹0%,10%⁶0%and 60%^elongation at break,respectively.The stability of the PS@Ag/PDMS strain sensor is further improved through a design of sandwich structure,and successfully demonstrated the monitoring human motion.5.The fabrication and properties of the polystyrene/graphene/silver nanowires multi dimensional hybrid conductive materials.Monodisperse cationic polystyrene microspheres?1.0?m?with amino groups were synthesized via dispersion polymerization method,and the polystyrene/graphene hybrids were prepared by electrostatic adsorption due to the opposite charges of cationic polystyrene with positive charge and graphene oxide?GO?with negative charge.After the reduction action of GO,a three-dimensional conductive network of rGO was formed along the surfaces of PS microspheres,which show a low percolation less than 0.2vol%.Silver nanowires?AgNWs?with high aspect ratio were introduced into the PS/rGO hybrids to fabricate PS/rGO/AgNWs multi dimensional hybrid conductive materials.The unique structure improved the electrical conductivity of PS/rGO/AgNWs,and the synergistic mechanism of rGO and AgNWs was investigated.