Applications Exploration Of Graphene For High-Performance Thermal Conductive And Strain Sensing Composites

Graphene has excellent thermal,electrical,mechanical and optical properties,which provide graphene a great potential for applications in thermal management,sensors,mechanical reinforcement,transparent conductive films and energy storage.Single-layer graphene has been demonstrated to have a thermal conductivity of 5300 W/mK,which is 10 times higher than that of copper.Meanwhile,it has a good electrical conductivity compare to copper.Such high thermal conductivity and electrical conductivity of graphene have triggered tremendous research interest in high-performace composites,especially in the field of polymer composites.This dissertation focus on the design and synthesis of thermal/electrical condulctive networks of graphene in natural rubber(NR)and their applications in thermal conductive composites and strain sensors.The main results are shown as follow.(1)The aligned graphene nanosheets/graphene foam/NR(GNs/GF/NR)composite was designed and synthesized,which shows effective enhancement of thermal conductivity at a low graphene loading.The in-plane and cross-plane thermal conductivity of GNs/GF/NR can reach 10.64 and 3 W/mK,respectively,at 6.2 vol%graphene loading.Compared to NR,the GNs/GF/NR composites shows a record thermal conductivity enhancement(TCE)of 8100%ever reported at room temperature,and a record-high TCE per 1 vol%graphene(specific TCE)of 1300%.Moreover,a clear thermal percolation was observed at a low graphene loading of 6.2 vol%,leading to a sharp increase in thermal conductivity.Further analyses reveal that the a significant synergisitic effect between the aligned GNs and 3D interconnected GF plays a key role in the formation of a thermal percolation network and then remarkably improve the themal conductivity of the composites.The highest in-plane and cross-plane synergistic effect is 127%and 233%,respectively,at 6.2 vol%graphene loading fraction.Additionally,the use of GNs/GF/NR composite for heat dissipation of high-power light-emitting diode(LED)lamps was demonstrated.Compared with NR,the temperature of LED with GNs/GF/NR composite as a heat spreader can be lowerd by 29.8 ? and as thermal interface material can be decreased by 14.9 ?.These results demonstrate the great potential of GNs/GF/NR composite materials for efficient heat dissipation in electronic devices.(2)GNs/GF/NR composites with different glass transition temperatures(Tg)were synthesized through controlling the vulcanization conditions.The sliding of GNs in NR composites under strain was observed and the effect of GNs movement on the conductive network structure of GNs/GF/NR composite with different Tg was studied.Then,stretchable composite sensor with high gauge factor and controlled strain were fabricated.The highest gauge factor can reach 23022 with 100%strain and the highest strain can reach 230%with a gauge factor of 714.The relationship between resistance change and tensile strain was comprehensively studied for the GNs/GF/NR composites with different Tg.The results show that lower Tg of GNs/GF/NR composite leads to overlap of GNs under strain and more conductive paths,thus a lower slope for the ratio of resistance change to tensile strain,and larger tensile strain.In contrary,the higher Tg is,the easier the GNs tend to separate directly under strain,which results in smaller tensile strain of GNs/GF/NR.Additionally,the high-performacne GNs/GF/NR strain sensor was used to monitor human motions ranging from small strain like wrist and finger bending to large strain including elbow and knee bending.The sensor can distinguish the details of motions accurately.The strain sensor was further applied in robot remote control and the results indicate that the elbow and arm of robot can synchronize with the human elbow and arm motion accurately.Such high-performance strain sensor shows great potential in human motion monitoring,electronic skin and intelligence materials.