Properties and Nano-observation of Natural Rubber with Nanomatrix Structure - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 322

morPholoGy oF NaNomatriX struCture
Recently, a serious problem on TEM images was suggested by Jinnai and co-workers,
on the basis of computer simulation and observation of the phase separated structure
of a block-copolymer through transmission electron micro-tomography, TEMT (Kato
et al., 2007). The transmitted electron beam throughout an ultra-thin section made an
apparent two-dimensional image, different from a real object, because of a thickness
of the section (Kaneko et al., 2005; Kawaseet al., 2007). In other words, the TEM
image is just a projection of three-dimensional entity; hence, structural information
along a beam-through direction, perpendicular to the plane of the specimen, that is,
Z-direction, may be lost. To obtain the real image of the phase separated structure,
therefore, we must perform the three dimensional observation for the nanomatrix
structure. The three dimensional image is made by stacking tomograms reconstructed
from a series of tilted transmitted two dimensional images, which are taken by TEM.
Although a resolution along the Z-direction is known to be less than that in the speci-
men plane, we may recognize the real structure through the Z-direction. Furthermore,
we have to take a notice of a diameter of the dispersoid of the nanomatrix structure,
which is about a micro-meter in diameter. Since, the thickness of the ultra-thin section
is less than several hundred nm, the three-dimensional image is not obtained for the
nanomatrix structure as long as we adapt TEMT; that is, the TEMT image is similar
to the two-dimensional TEM image. To observe the nanomatrix structure in a range of
nano-metric scale and micro-metric scale, thus, we have to apply not only TEMT but
also recently proposed dual beam electron microscopy, that is field-emission scanning
electron microscopy equipped with focused ion beam, FIB-SEM (Beach et al., 2005;
Brostow et al., 2007; Kato et al., 2007). Using these techniques, we shall investigate a
relationship between the properties and three-dimensional structure for the nanomatrix
structured material.
After alignment of the observed images of surfaces of DPNR- graft -PS, which
were sliced with the focused ion beam at each 102 nm interval, a three-dimensional
image was made for the nanomatrix structure, as shown in Figure 8 . Since the sur-
faces were completely flat, without damage or void, we successfully constructed the
three-dimensional image of the nanomatrix structure in micro-metric scale. At this low
magnification, the brighteach other in all directions. The natural rubber particles were
positively confirmed to be dispersed into the nanomatrix of polystyrene.
The TEMT observation at high magnification makes possible to investigate the
matrix, precisely. The three-dimensional TEMT image is shown in Figure 9. A curva-
ture of the natural rubber particles was well-shown in the image, in spite of a limitation
of thickness of the ultra thin section, that is about 100 nm. The natural rubber particles
of various dimensions were randomly dispersed in the polystyrene matrix, reflecting
a broad distribution of the particle dimension, that is 50 nm-3 µm in volume mean
particles diameters (Kawahara et al., 2001). The three-dimentional image reveals not
only the connected matrix but also it defect, at which rubber particles are fused to each
other.