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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


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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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.

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