3. Results and discussion
The scanning electron micrographs are illustrated in Figure 1 for the
graphene that solves the problems regarding insufficient exfoliation of
the graphite powder and deterioration in the electrical conductivity and
thermal conductivity. Graphite is a stack of graphene sheets bound by
van der Waals interactions, each graphene layer being made ofsp 2 carbons distributed in a hexagonal crystal
structure. Graphene has superior mechanical, electrical, and thermal
properties. In bottom-up methods to produce graphene, for example,
chemical vapor deposition, graphene is synthesized. In top-down methods,
for example liquid-phase exfoliation, graphene sheets are separated from
bulk graphite material. The bottom-up approach produces low quantities
with high quality and large flakes. The top-down approach using graphite
is low in cost and yields a high concentration of suspended flakes, but
fabricates limited-size sheets with a low yield of mono-layer graphene.
Existing commercially available graphene products usually contains
precipitates of graphene due to the presence of thick layers of graphene
and are not stable. The method of the exfoliation of graphene from
graphite using multilayer coextrusion is described herein. Graphite is
dispersed within a first processing material, and the first processing
material and a second processing material are co-extruded through a
plurality of series coupled layer multiplication dies to exfoliate
graphene from the graphite. The graphene is separated from the resulting
multi-layered material. Graphite flake and expanded graphite may be
dispersed within the first processing material. The process uses an
organic solvent and silica under high pressure sheer force to create a
liquid intermediate containing thin layers of graphene that allows for
easy dispersion of graphene in a liquid organic solvent system. High
sheer processing of graphene and silica together in a liquid organic
solvent system result in stable graphene platelets. During the process,
thick layers of graphene can break down to smaller layers of graphene
that is more usable. The silica forms a gel simultaneously as graphene
platelet multiple stacks are sheered into smaller platelet stacks
through the organic solvent carrier. The small platelet stacks are
dispersed in the gel and held by the network of the gel stably. In the
process, both a graphene raw material and silica are mixed in an organic
solvent to form a liquid precursor. Preferably, the graphene raw
material is a graphene powder. The graphene raw material may be obtained
commercially. Commercially available graphene usually contains thick
layers. Thus, when commercially available graphene is used as an
additive or is added to a liquid product, the commercially available
graphene may precipitate in the liquid product.