2. Methods
A technical feature of the method for manufacturing graphene is that the method includes exfoliating or transferring a graphite material onto at least one structure to form graphene particles on the surface of any one of the at least one structure, releasing the graphene particles from the structure, and combining the released graphene particles to form graphene. The step of forming graphene particles includes: exfoliating the graphite material onto a first structure of the plural structures to form first graphene particles on the surface of the first structure; and transferring the first graphene particles to a second structure disposed opposite to the first structure out of the plural structures to form second graphene particles. The step of forming graphene particles may include exfoliating or transferring the graphite material onto the surface of rollers used as the structures to form the graphene particles, the rollers being different in diameter from each other and rotating in contact with each other. Preferably, the step of forming graphene particles may include exfoliating or transferring the graphite material onto the surface of rollers and a plate used as the structures to form the graphene particles, the rollers being different in diameter from each other and rotating in contact with each other, the plate moving in a linear reciprocating motion in contact with the rollers. The step of forming graphene particles includes: applying the graphite material between first and second structures making a pair out of the plural structures; exfoliating the graphite material onto the first and second structures to form first graphene particles on the surface of the first and second structures, respectively; and transferring the first graphene particles to third and fourth structures disposed opposite to the first and second structures out of the plural structures, respectively, to form second graphene particles on the surface of the third and fourth structures, respectively. The step of forming graphene includes injecting an adhesive liquid for constraining the released graphene particles and then applying pressure on the released graphene particles to combine the graphene particles. An adhesive layer for exfoliation, transfer or release of the graphene particles may be provided on the surface of the structure. A rubber elastomer may be applied or mounted as the adhesive layer on the surface of the structure. The rubber elastomer may be silicone rubber. The method may further include applying the graphite material together with an adhesive liquid or solid onto the structure. A technical feature of the method for manufacturing a conductor is that the method includes: applying or forming the graphene manufactured by the graphene-manufacturing method on a sheet or a film to make an electrical conductor or a thermal conductor.
In the present study, the term nanofluid describes a homogeneous dispersion of at least a nanomaterial with at least one dimension in a nanoscale in a conventional base fluid. In the present study, the nanomaterial refers to graphene-based compounds or composites. The present study relates to a nanofluid characterized in that it comprises a liquid medium selected from an organic solvent or a water solution of acidic, neutral or basic compounds and said liquid medium optionally comprising a surfactant, and a graphene-based compound or composite, homogenously dispersed in the liquid medium, and the graphene-based compound or composite optionally comprising a material associated to the graphene-based compounds. The term graphene-based compound or composite refers herein to graphene, graphene oxide, reduced graphene oxide or a combination thereof forming either compounds or composites with any other molecule, polymer or solid phase in extended or nanoparticulate form. The graphene-based compound of the nanofluid is in a nanoparticle volume fraction between 0.0008 percent and 0.008 percent based on the total weight of the electroactive nanofluid. Nanofluids are prepared by direct mixing of the graphene-based compound or composite and the liquid medium. The graphene-based compound or composite optionally comprises substances either attached to the graphene-based compounds or forming a mixture by dispersion in the base fluid. The nanofluid may further comprising carbon materials such as activated carbons or carbon nanotubes aside from graphene. Each of these present specific advantages such as low cost or anisotropy which expand the possible applications of the nanofluids. Graphene oxide is synthesized from natural graphite using the modified Hummers method. Graphene oxide nanosheets exhibits pores in mesopores as well as macro-porous region. Enhancements in the thermal conductivities of nanofluids, for the most part, follow the predictions based on Maxwell’s mean field theory assuming low concentrations and spherical nanoparticles or the effective medium theory. Thermal conduction in nanofluids is attributed to a variety of mechanisms, including Brownian motion interactions between the nanoparticles and the fluid, clustering and agglomeration. There is no clear consensus on a specific mechanism; however, the general belief is that a combination of mechanisms may be operating and would be specific to a nanoparticles-fluid system and test conditions. Further, the effect of interface layers on the nanoparticles on thermal conductivity is not clearly understood. A metal particle with surface oxidation, for example, continuously increases the interfacial resistance and consequently reduce the thermal conductivity. Some of these nanofluids also can include a surfactant additive to stabilize particle suspensions. Because thermal conductivity of surfactants is very poor compared to water, often more preferred water-based nanofluids are comprised of functionalized graphene wherein as received graphene is treated by oxidation, such as by mixing with concentrated sulfuric and nitric acids. Such oxidized, or functionalized, graphene is disposed in fluids without need of surfactants to achieve greatly improved thermal properties for the nanofluids.