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.