Research On Piezoresistive Performance Of Nanocarbons/Silicone Rubber Composites Based On Conductive Structure Construction

Conductive polymer nanocomposites(CPNCs)are one of the most promising classes of piezoresistive materials that exhibit excellent performance such as flexibility,low cost,nontoxicity,durability,as well as easiness of producing.By composing conductive fillers into polymer matrix as nanocomposites,a piezoresistive material of CPNCs is obtained.It has emerged as a highly active field due to promising applications in various tactile devices,such as artificial electronic skin,artificial intelligence systems and wearable health care devices.However,a key limitation for the practical application of conventional CPNCs is the poor sensitivity in low pressure regimes(<100 kPa).Such pressure regimes are very important for approximating gentle touch and object manipulation,which largely limit its wide application.Therefore,the preparation of CPNCs with high sensitivity among finger-sensing regimes(0-100 kPa)is the biggest challenge for CPNCs.Studies have shown that a small amount of multi-walled carbon nanotubes(MWCNTs)or graphene nanosheets(GNPs)which are added to a typical silicone rubber matrix(poly(dimethylsiloxane),PDMS)will make CPNCs with high piezoresistive sensitivity.However,due to the structural and physical properties of nanocarbons,the poor compatibility in solvent and problems of bad dispersion as well as weak interfacial interaction in PDMS matrix result in decreasing of piezoresistivity,high cost,destroying of flexibility,high power consumption,largely limiting the widespread applications of CPNCs.To resolve these problems,this paper based on the percolation theory and tunneling effects between nanocarbon fillers,and piezoresistive mechanism of deformation-induced conductive networks reconstruction in nanocomposites.In this study,nanocarbons/silicone rubber composites is chosen as the research object.The structure of conductive fillers are constructed by noncovalently functionalized technology,and nanocomposites are preparated by the method of injection moulding.The structure modifications of conductive networks and piezoresistive sensitivity enhancement are achieved by adjusting the process conditions,and elucidation of structure-to-property relationships of piezoresistive carbon nanomaterials filled PDMS-based nanocomposites are investigated,as following:These devices usually require high-performance nanocomposites with properties of high piezoresistive sensitivity(S),low Young's modulus(E)and high electrical conductivity(?).Poly(phenylmethylsiloxane)(PPMS)functionalized multi-walled carbon nanotubes(P-MWCNTs)is introduced into poly(dimethylsiloxane)(PDMS)matrix to obtain P-MWCNTs/PDMS nanocomposites with high performance.The P-MWCNTs with core-shell structure exhibits excellent compatibility in chloroform and homogenous dispersion in PDMS matrix,which is the effective method to dramatically improve the electrical,elastic and piezoresistive properties of nanocomposites.Slightly above the percolation threshold(0.74 vol.%)content,the P-MWCNTs/PDMS nanocomposites with 0.75 vol.%of P-MWCNTs shows high performance of S of 8.09 × 10-3 kPa-1 at regimes(0-100 kPa),low E of 489.50 kPa and high ? of 1.24 x 10-4 S/m.Poor sensitivity in low pressure regimes(<100 KPa)of CPNCs is one of their major disadvantages compare to other piezoresistive materials.The reasons induced the poor sensitivity include bad dispersion and week interface of multi-walled carbon nanotubes(MWCNTs)applied in poly(dimethyl siloxane)(PDMS).A novel vinyl-terminated poly(dimethyl siloxane)-poly(phenylmethyl siloxane)-multi-walled carbon nanotubes(V-P-MWCNTs)with core-dualshell nanostructure is fabricated by noncovalently functionalized method.The V-P-MWCNTs as conductive fillers exhibites homogenous dispersion as well as good interfacial interaction in PDMS matrix.Slightly above the percolation threshold(0.19 vol.%),the PDMS-based nanocomposites with 0.2 vol.%of V-P-MWCNTs showes high piezoresistive sensitivity(22.16 x 10-3 kPa-1).Microstructures of conductive networks and spatial distribution of conductive fillers in polymer matrix play important roles in determining piezoresistive behavior of CPNCs.In this work,poly(dimethyl siloxane)-based(PDMS-based)nanocomposites with tunable piezoresistive sensitivity via different aspect ratio of functionalized multi-walled carbon nanotubes(functionalized MWCNTs,such as F-ARH or F-ARL),which could tune the above two issues simultaneously.Because of different microstructures and spatial distribution,the F-ARH/PDMS nanocomposites with low cost(fillers content as low as 0.20 vol.%)exhibits tunable piezoresistive sensitivity(from 6.56×10-3 to 22.16×10-3 kPa-1)while F-ARL/PDMS nanocomposites with low power consumption(conductivity as low as 3.12×10-3 S/m)exhibits tunable piezoresistive sensitivity(from 8.09×10-3 to 69.76×10-3 kPa-1).Nanostructures of conductive fillers often play a significant role on forming conductive networks in polymer matrix.Functionalized conductive fillers in polymer-based nanocomposites with outstanding electrical,elastic,and piezoresistive properties have potential applications in piezoresistive materials.Herein,poly(phenylmethylsiloxane)functionalized graphene nanoplatelets(P-GNPs)are introduced into poly(dimethylsiloxane)(PDMS)matrix to obtain P-GNPs/PDMS nanocomposites.P-GNPs with sandwiched nanostructure exhibits homogeneous dispersibility and outstanding compatibility in PDMS matrix,which is an effective method to dramatically improve electrical,elastic and piezoresistive properties of nanocomposites.Slightly above the percolation threshold(2.96 vol.%)content,P-GNPs/PDMS nanocomposites with 3.00 vol.%of P-GNPs shows high piezoresistive sensitivity(S)of-105.22×10-3 kPa-1 at regimes(0-10 kPa),low Young's modulus(E)of 408.26 kPa and high electrical conductivity(a)of 1.28x 10-6 S/m.