SEBS-domains appear black and the PP-phase appears white.
It is quite difficult to judge whether the SEBS-domains are
dispersed or continuous with the PP phase. The 3D model of
this blend obtained using electron tomography is shown in
Fig. 6(b). The model shows a SEBS-contour that resembles a
complicated double gyroid structure. Although the cocontinuous
morphology of the SEBS-phase has been studied
in the past [15] using confocal scanning laser microscopy,
solvent extraction methods, mechanical properties and rheology,
the present method gives a direct view of the 3D-structure
of these polymer blends at a resolution higher than any of the
methods previously reported.
The utility of tomography is twofold: first, it provides a 3Dexamination
of features, without the need for serial section
analysis; second, because the computed slices through the
tomographic volumes can be much thinner than is possible to
produce by physical sectioning, it reveals structural details in
the range of 5–30 nm that tend to be obscured in conventional
thin sections [16,17]. In biological sciences, tomographic
analysis has forced reassessment of long-standing views of
organelles such as mitocohondria and Golgi apparatus [16,17].
While biological sciences have a long history of tomographic
reconstruction it has rarely been used for materials science.
There are several reasons for this:
(a) Bright field TEM imaging leads to undesirable diffraction
contrast from crystalline specimens. By using an imaging
technique, which is insensitive to diffraction contrast,
such problems may be reduced or eliminated.
(b) Most material specimens can often be described by 2D
TEM projections. This assumption is however not valid
for polymer blends especially with high loadings of the
rubber phase.
(c) Until recently, tomography used to be an expensive
technique, both in terms of the instruments used and the
computational resources required. However, there has
been a significant improvement in computing power
during the last two years. Softwares and hardwares for
reconstruction are both freely available (ex IMOD) and
relatively cheap.