Preparation And Application Of Flexible Conductive Materials With High Mechanical Stability And Conductivity

Material-induced flexibleand structure-induced flexible conductors exhibit great potential applications,and possess advantages of high conductivity and stable electrical performance,while they are deformed.The material-induced flexibility is achieved by using materials with extraordinary mechanical and electrical properties.The structure-induced flexibility is achieved by either using an intrinsic flexible material,structural flexibility,which can be introduced by structural features,such as a 3D pore system,or by a combination of both.In order to obtain good performance of stretchability and compressibility,sponge-like structures are utilized.Liquid metal sponges were fabricated by loading liquid metal(Ga In Sn)into elastomer sponges.Hence,not only the material itself can be stretched,but the sponge-like structure increases the stretchability.The elasticity of 3D-interconnected networks and the fluidic nature of liquid metals lead to the formation of all-soft structures for electric conductors with high electrical conductivity and mechanical flexibility.The main results are as follows:We report for the first time on the material-induced flexibility,which was achieved via a low cost,solution-processed,and microfluidic approach,for patterning metal structures on chemically modified polyethyleneterephthalate(PET)thin films by in situ polymer-assisted electroless deposition(ELD).To validate this method,we have successfully fabricated patterns of copper,silver,and nickel on PET substrates with unprecedentedly electrical conductivity and excellent mechanical flexibility.Our results show that the conductivity of the as-made metals is comparable to that of the corresponding bulk metals,i.e.,3.0 × 107 S m-1,5.2 × 107 S m-1,and 1.0 × 107 S m-1,for Cu,Ag,and Ni,respectively.These results are among the best for metals prepared by ELD.Remarkably,the as-made metal-PET exhibits a stable conductivity even upon a large number of bending cycles(e.g.,5000)at different bending curvatures.We further demonstrate that the as-made metal-PET composites are capable for long-term applications,such as flexible conductors and their flexible LED circuits.Further more,we report a low-cost,solution processed,versatile approach based on structure-induced flexibility to fabricate flexile conductors out of 3D porous PDMS sponges by a combination of surface modification with polymers and consequent electroless metal deposition.To validate this method,we have successfully fabricated Cu-,Ag/Cu-,and Au/Cu-PDMS sponges as well as the flexible circuits to light up light-emitting diode(LED)arrays.The as-made metal-sponges exhibited good electric conductivity and mechanical stability,such as stretchability and compressibility.Our results signify that the resistance of the as-fabricated composite sponge virtually maintains a constant conductivity under a large number of cycles(up to 5000)of repeated stretching and compressing.3D-interconnected porous sponges made of an elastomer such as PDMS were utilized as a 3D skeleton for storing and supporting the liquid Ga In Sn metal.Notably,PDMS sponges are highly stretchable,not only due to the elasticity of the material itself,but also due to the flexibility of the sponge-like structure.To validate this strategy,we first constructed conductive PDMS sponges by loading with different quantitiesof liquid metal to varying geometries of sponges.The resulting composites achieved a maximum conductivity(1.62 x 104 S/cm),which is comparable to that of bulk Ga In Sn.Afterwards,we systemically investigated the stretchability and durability of the as-made Ga In Sn PDMS sponges.Our results show that the resistance of the composites only slightly changes upon exerting of tensile strain,i.e.10% change in resistivity at 50% tensile strain,and the resistance is virtually constant for 10000-stretching cycles at tensile strains ranging from 10% to 50%.As proof-of-concept,we successfully demonstrated the application of stretchable circuits made out of Ga In Sn PDMS sponges packaged into soft elastomers as interconnects to light up arrays of LED lamps.