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Microscopy
Easiest and most common method ofcharacterization
Limited to the pores at the surface
Optical microscopy can be used for porediameters down to 50uM.
Smaller structures can be imaged using
electron microscopy.
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Light Microscope Electron MicroscopeCheap to purchase Expensive to buyCheap to operate. Expensive to produce electron beam.Small and portable. Large and requires special rooms.Simple and easy sample preparation. Lengthy and complex sample prep.Material rarely distorted by preparation. Preparation distorts material.Vacuum is not required. Vacuum is required.Natural color of sample maintained. All images in black and white.Magnifies objects only up to 2000 times Magnifies over 500 000 times.Specimens can be living or dead Specimens are dead, as they must be fixed in
plastic and viewed in a vacuumStains are often needed to make the cells
visibleThe electron beam can damage specimens
and they must be stained with an electron-
dense chemical (usually heavy metals like
osmium, lead or gold).
Comparison of the light and electron
microscope
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Two main varieties or electron microscopy is in use.
Scanning Electron Microscope
Usually uses a electron gun (hottungsten filament) to raster an e-
beam over the surface.
Some of the incident electrons are
scattered and can be detected.
Scattering intensity is proportional
to the surface area of the incident
electron spot and the material type.
A steep surface has a larger surface
area and thus greater scatteringsignal. This gives topographic
resolution.
Resolution from 1nm to 20nm
Can image relatively large area of
sample
Transmission Electron Microscope
Angstrom level resolution (latticeresolution)
Requires the sample to be transparent to
electrons (very thin)
Electrons either scatter off atoms in the
sample or pass through.
Information is gathered in two ways:
1. Electron diffraction pattern in
reciprocal space at the back-focal plane
2. Image in real space located at the
image plane.
Images only a relatively small area of
the sample.
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Secondary Electron Imaging
(SEI)
Transmitted Electron Imaging
(TEI)
Backscattered Imaging
(BSI)
Surface Topography,
Morphology, Particle
Sizes, etc.
Compositional Contrast
Internal ultrastructure Energy-Dispersive
X-ray Spectrometry
(EDS)
Elemental composition,
mapping and linescans
Crystallographic Info
Electron Backscattered Electron
Diffraction
(EBSD)
SEM Capabilities
Scanning Electron Microscope
(SEM)
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Electron Diffraction
(ED)
High-Resolution
Transmission Electron Microscopy
(HR-TEM)
Bright- and Dark-Field Imaging
(BF/DF imaging)
Crystallographic Info Internal ultrastructure
Nanostructure dispersion
Defect identification
Interface structure
Defect structureEnergy-Dispersive
X-ray Spectrometry
(EDS)
Elemental composition,
mapping and linescans
Chemical composition
Other Bonding info
Electron Energy Loss Spectroscopy
(EELS)
TEM Capabilities
Transmission Electron Microscope
(TEM)
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Karge and Weitkamp p.87
TEM can obtain lattice resolution for microporous materials
LTL zeolite is an
example of aporous material
with 3 different
size pores.
It has 6, 8, and 12
member rings.
TEM has the
ability to image
each of these pores.
The 12 memberrings are only 7
Angstroms in
diameter.
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S. X. Wang, L. M. Wang and R. C. Ewing, " Electron irradiation of zeolites",Mat. Res. Soc. Symp. Proc. 540 (1998)
Zeolite-Y looking down [011] direction.
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Improved properties related to the
dispersion and nanostructure (aspect
ratio, etc.) of the layered silicate inpolymer
The greatest improvement of these
benefits often comes with exfoliated
samples
Intercalate: Organic component insertedbetween the layers of the clay
Inter-layer spacing is expanded, but
the layers still bear a well-defined
spatial relationship to each other
Exfoliated: Layers of the clay have been
completely separated and the individuallayers are distributed throughout the
organic matrix
Results from extensive polymer
penetration and delamination of the
silicate crystallites
http://www.azom.com/details.asp?ArticleID=936
Layered Silicates (Nanoclay) and Polymer Nanocomposites
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Polymer-Layered Silicate Nanocomposites
Organoclay nanocomposite (10% inNovalac-Based Cyanate Ester)
XRD gives average interlayer d-spacing
while TEM can give site specific
morphology and d-spacing
In this case, XRD gave no peaks
Many factors such as concentration
and order of the clay can influence
the XRD patterns
XRD often inconclusive when usedalone
TEM of Intercalated Nanoclay
Alexander B. Morgan, and Jeffrey W. Gilman, Characterization of Polymer-Layered Silicate (Clay) Nanocomposites by
Transmission Electron Microscopy and X-Ray Diffraction: A Comparative Study, J. Applied Polymer Science, 87 1329-1338 (2003).
P l L d Sili N i
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Polymer-Layered Silicate Nanocomposites
In the authors own words:
The majority of PLSNs that we
investigated were best described as
intercalated/exfoliated. By XRD,
they would be simply defined as
intercalated, in that there was an
observed increase in the d-spacing as
compared to the original clay d-
spacing. However, the TEM images
showed that although there were
indeed intercalated multilayer
crystallites present, single exfoliated
silicate layers were also prevalent,
hence, the designation of an
intercalated/exfoliated type of
PLSNs.
TEM Image of an
Intercalated/Exfoliated PS
Nanocomposite
Exfoliated
Single Layers
Small Intercalated
Clay Layers
Alexander B. Morgan, and Jeffrey W. Gilman, Characterization of Polymer-Layered Silicate (Clay) Nanocomposites by
Transmission Electron Microscopy and X-Ray Diffraction: A Comparative Study, J. Applied Polymer Science, 87 1329-1338 (2003).
E B d Cl N it
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Epoxy-Based Clay Nanocomposites
Change of basal spacing of organo-clay nanocomposites during processing of epoxy/clay
nanocomposites by the sonication technique
TEM images of nanoclay in different epoxy systems showing intercalated(white
arrows)/exfoliated (black arrows) nanocomposite hybrids
Increase in basal d-spacings in nanoclay platelets observed by TEM and XRD
In some cases from 1.8 nm up to 8.72 nm
Hiroaki Miyagawa, Lawrence T. Drzal, and Jerrold A. Carsello, Intercalation and Exfoliation of Clay Nanoplatelets in
Epoxy-Based Nanocomposites: TEM and XRD Observations, Polymer Engineering and Science, 46(4) 452-463 (2006).
TEM Images of Clay/Epoxy Nanocomposites
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Alexander B. Morgan, and Jeffrey W. Gilman, Characterization of Polymer-Layered Silicate (Clay) Nanocomposites by
Transmission Electron Microscopy and X-Ray Diffraction: A Comparative Study, J. Applied Polymer Science, 87 1329-
1338 (2003).
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CONCLUSIONS
We have shown several different PLSNs of varying nanoscale dispersions, comparing
and contrasting the results by XRD and TEM. In light of these results, the definitionsused to describe PLSNs should be modified to more accurately describe the
dispersion at the nanoscale. Two of the definitions are still quite useful in describing
the nature of the PLSN, namely, immiscible and exfoliated. To avoid confusion,
immiscible systems should probably be described as microcomposites rather than
as immiscible nanocomposites. The exfoliated systems do fall into two categories,
exfoliated ordered (PS) and exfoliated disordered (PA-6). The greatest clarification isneeded for the intercalated definition. Although some purely intercalated
nanocomposites have been made, they are not very common. As exfoliated
nanocomposites are generally the desired product of PLSN synthesis, attempts that
do not achieve exfoliation often fall into this mixed morphology category. The most
important observation determined from this study is that XRD results by themselves
cannot be used to adequately describe the nanoscale dispersion of the layeredsilicate present in PLSNs. XRD results when properly interpreted and combined with
TEM results give a much clearer picture of the actual nanoscale dispersion and
overall global dispersion of the clay in the polymer. Further, these two techniques
provide information to help derive meaningful relationships between the PLSN
nanostructure and macroscale properties.