Synthesis And Application Of Functional Polymer-based Composites With Thermal And Electrical Conductivity

Thermally or electrically conductive polymer composites comprising thermally or electrically conductive fillers are applied widely in heat conduction and electrical conduction.In this work,functional composites were developed for the heat dissipation of chip encapsulation,transparent and thermally conductive encapsulation materials of LED,flexible composite film heater and the electrodes of flexible electronics.The properties of thermal conductivity,electrical conductivity,electromagenetic shielding,mechanical strength,transparency,conductive recovery and so on were discussed.Silver-plating carbon fiber(APCF)was prepared by electroless chemical plating on the surface of carbon fiber.The thickness of Ag coating is 450 nm.Weight ratio and atom ratio of Ag coating on carbon fiber surface are 99.01% and 95.65%,respectively.No oxide phase of Ag was detected.Finally,the thermally conductive and electromagenetic shielding composites combining APCF and epoxy resin were prepared.With filling content of 4.5% and 7.0%,thermal conductivity increased up to 2.33 W/(m·K)and 2.49 W/(m·K),respectively.Volume resistance decreased from 1.7×1016 ?·cm to 9.5×103 ?·cm,as well as surface resistance from 6.9×1015 ? to 6.2×102 ?.Electromagenetic shielding effectiveness of the composite with 4.5% filling content is 38-35 d B during 8.2-12.4 GHz(X range),which indicates 99.9% wave was weaked.Impact strength and flexural strength of the composite with 7.0% filling content are 67 k J/m2 and 138.6 MPa,respectively.A transparent thermally conductive composite for LED encapsulation was prepared.The composite features a layer of silver nanowire percolation network embedded into the surface layer of a polymer substrate comprising a polyacrylate layer to confine the nanowires to the surface of a polyimide film and to attain low contact resistance between the nanowires.The transmittance of the composite films with sheet resistance of 40 ?/sq and 7 ?/sq is 82% and 76% at 550 nm,respectively.The sheet resistance of the composite film with 7±1 ?/sq increased to 16±3 ?/sq after heating for 168 h.Thermal conductivity of the composite films are comparable to commercial copper foil.A thermal diffusion apparatus was set up to check the lateral heat spread for the first time.The thermally conductive composite film was attached on the bottom surface of the thermal diffusion apparatus.The inside temperatures of the hemispherical thermal conductor were measured.Compared with polyimide film,with Ag NW/polyimide composite film as heat spreader the core temperature of the hemispherical thermal conductor decreased.A transparent heat-resistant flexible polyacrylate film was synthesized by three acrylate monomers under UV curing.The glass transition temperature is 140 ?,as well as the storage module up to 310 MPa at 200 ?,which indicates higher heat resistance than commercial PET.Then the transparent conductive Ag NW/polyacrylate composite was prepared by combining Ag NW network on the surface of the polyacryalte film.The transmittance of the composite films with sheet resistance of 60 ?/sq,25 ?/sq,15 ?/sq and 10 ?/sq is 89.5%,86.4%,84.4% and 81.0%,respectively.A composite film with a sheet resistance of 25 ?/sq performs saturation temperature up to 160 ? when applying voltage at 11 V.In order to reduce the heating time and obtain high saturation temperature,BN was filled into the polyacrylate matrix with a filling content of 3%,which increased thermal conductivity up to 0.46 W/(m·K).The Ag NW/BN/polyacyralte composite film generated heat up to 138 ?,which decreased to 136 ? after 1080 min.Flexible conductive materials have significant effect on developing flexible electronics.Especially,flexible composite conductor with self-healing ability can recover conductivity.In this work,a Diels-Alder polymer(P(FR-BME))is synthesized by two monomers with furan group and malimide group,respectively.A Ag NW/P(FR-BME)composite film was prepared by an ultrathin polymer intermediate layer(P(PA-FM))confining Ag NW conductive network on the surface of healable polymer P(FR-BME).The transmittance of Ag NW/P(FR-BME)composite film with sheet resistance of 18 ?/sq is 80% at 550 nm.A composite film with initial resistance of 18 ? lost the conductivity after cutting,while the composite conductor can recover resistance to 21 ? after heating at 100 ? for 6 min.The healing efficiency was up to 97%.Multiple healing on the same location performed after three cycles of cut-healing at 100 ?.The resistances after each cycle were 21 ?,60 ? and 700 ?.The first healable capacitive touch screen was developed by Ag NW/P(FR-BME)composites for the first time.The healing efficiency of the P(FR-BME)substrate can be improved by MWNT as fillers.With a filling content of 0.5%,thermal conductivity of MWNT/P(FR-BME)composite was 0.46 W/(m·K).The conductive elastic polymer(FM-DA)maintained high conductivity during stretching and released,as well as conductive recovery after repeated cycles of stretch-release.Healable conductive elastomer was prepared by Diels-Alder reaction.30% prestrained Ag NW/PEDOT/FM-DA composites was synthesized with PEDOT as an intermediate layer,which performs a tunable bonding between Ag NW and FM-DA.The sheet resistance of Ag NW/PEDOT/FM-DA composite conductor with 15 ?/sq can be recovered to 18 ?/sq.Compared with the fresh composite film,the resistance increased 3 ? and 68 ? when 30% and 60% stretching,respectively.PEDOT as the conductive layer would offset the conductive loss between disconnected Ag NW.The baseline resistance and peak resistance of the elastomer with 15 ? increased to 20.3 ? and 32.0 ?,respectively,after 800 cycles stretching.