Graphite is famously anisotropic. Single crystals are
excellent thermal conductors in two dimensions (a-axes) and poor conductors in
the third (c-axis). While it may be impossible to improve on graphite as
a thermal conductor, the following image suggests one way to improve graphite
as an insulator.
The discontinuities in this
origami sample should accentuate the already high anisotropy of
conventional graphite. While c-axis conduction within dense graphite
sheets is about three powers of ten poorer than a-axis conduction, heat must
between sheets through narrow, sparse contacts.
Discontinuously stacked origami graphite will impede all three modes of thermal transport:
- Radiation: Highly oriented graphite is reflective,
in contrast to the dielectrics used in typical thermal insulation.
- Convection: Highly oriented graphite is composed of
broad, dense graphene molecules, which are less permeable than fibrous or
open-cell foam insulating materials.
- Conduction: C-axis conduction in graphite is
already remarkably poor for an electrically conductive, reflective material.
The contacts between sheafs of discontinuously stacked origami graphite will
be narrow, sparse--and thus insulating--because of the unusual stiffness of
C-axis conduction in discontinuous origami graphite
will be especially poor if the discontinuities are numerous. Numerous,
thin graphite sheafs are desired. The
following micrograph shows that origami of nanoscale thickness can be
Isolated graphite sheets of only
several nanometers thickness are easily produced by splat-cooling. We
might produce thick, low density stacks of these membranes for thermal
insulation by precipitating graphite onto an evolving curved melt surface.