Exploring the Layered Structure of Composite Films Using an FTIR Microscope

Exploring the Layered
Structure of Composite Films
Using an FTIR Microscope
Shimadzu Scientific Instruments, Columbia, MD

Introduction
Multi-layered materials are commonly used in various industries, such as packaging,
construction and medical. Multi-layered structures may alter the mechanical, acoustic
and optical properties of materials. Identifying the chemical composition of different
layers by studying the cross section of a multi-layered film is important in research and
development of composite materials.
With the aid of the Shimadzu AIM-9000 FTIR microscope, infrared spectra can be
acquired with spatial resolution on the order of 10 microns along the cross section of
composite films. Analysis of the FTIR spectra helps to understand the formulation of
different layers the polymer film is composed of.

Experimental
The AIM-9000 FTIR microscope was set up in combination with the IRTracer-100
FTIR spectrophotometer. The AIMsolution and LabSolutions IR software suites were
used to maneuver the microscope and to set the experimental parameters. The
optional mapping software allowed for scanning and measuring samples in the points,
line or area modes.
The “line” mode was particularly useful in the investigation of the cross section of a
film sample. By setting an appropriate aperture size, an optimal signal was obtained
while maintaining high spatial resolution over the cross section of composite films.
Parameter Value
Instrument Shimadzu AIM-9000 FTIR Microscope
Shimadzu IRTracer-100 FTIR Spectrophotometer
Ge ATR accessory for AIM-9000 FTIR Microscope
Optical Mode Absorbance, Reflectance, ATR
Detector Mid-band MCT detector with liquid nitrogen cooling
Spectral Range 4000-700 cm-1
Resolution 8 cm-1
Number of Scans 64
Table I: Experimental Parameters

Experimental
Sample preparation is of vital importance in this experiment. The composite film under
study was received from a commercial source. It was white in color and laminated on
both sides. The sample was first cut to a smaller size of approximately 0.5 cm x 0.5
cm. It was then loaded onto a microtome and cut into thin slices appropriate for a cross
section study under an optical microscope.
The cut thin slices of the polymer film were subsequently loaded onto a diamond
window under a binocular optical microscope.
Cares were taken in the placement of the sample such that the cross section can be
observed in the field of view. The sample was then transferred to the AIM-9000 FTIR
microscope for infrared investigation.
Figure 1. The composite film was loaded onto a microtome and cut
into thin slices for cross section studies. The cut slices were loaded
onto a diamond window and transferred to the AIM-9000 FTIR
microscope

Experimental
The Shimadzu IRTracer-100 is a versatile FTIR bench that is capable of measuring in
the Mid-IR, NIR and FIR range. When used as the light source to drive the AIM-9000
FTIR microscope, it is measuring in the Mid-IR range. It utilizes a 30⁰ interferometer
and the mirror speed is set at 9 mm/s.
The AIM-9000 FTIR microscope measures the sample in the transmittance, reflectance
or ATR mode. A wide-field camera and an 15x objective are installed, allowing
convenient sample image zooming from macro size (10x13 mm) to micro size (300x
400 µm) The sample stage can move in a 70 x 30 mm area.
Figure 2. The Shimadzu AIM-9000 FTIR
microscope system used to measure the cross
section of the polymer film samples

Results & Discussion
The front and back side of the film have different chemical compositions. FTIR spectra
of both sides were acquired by using an Attenuated Total Reflectance (ATR)
attachment with a Ge crystal. Individual peak analysis and the search software
revealed that one side of the film is polyethylene, while the other side is 84%
petrothene NA 117 (mixture of polyethylene and monomer) and 16% polyamide.
Figure 3. FTIR spectra of the two
sides of the polymer film sample. One
side (red) is polyethylene; the other
side (black) is 84% petrothene NA 117
and 16% polyamide

Results and Discussion
FTIR spectra of the film’s cross section were acquired using the Shimadzu AIMsolution
software. Using the “line” mode of the optional mapping software, a series of
measurement spots were placed along the direction of a preset line. The aperture
sizes were set as 10x50 µm to allow for fine spatial resolution across the cross section
while maintaining sufficient signal level (Figure 4).
The spectral difference from one side of the
film to the other can be identified by
comparing peak intensities of a few IR
modes.
Figure 4. Heat map of the mode at 2912 cm-1.
The aperture size of 10x50 µm ensures fine
spatial resolution across the sample.

The peak at about 2912 cm-1 was attributed to symmetric and antisymmetric stretching
of the C-H bond. Since a concentration gradient of –CH2- exists over the cross section,
the peak intensity of this IR mode serves as a good indicator of varying chemical
compositions. A monotonic change of the peak intensity was observed from one side of
the sample to the other (Figure 5).
Peak intensity analysis can be
applied to other IR modes as well.
Figure 5. IR mode at about 2912 cm-1
over the cross section of the sample.
A monotonic intensity decrease was
observed from the lower side to the
upper side of the sample.

In Figure 6 and Figure 7, peak intensity analysis was applied to the C=O bond at
about 1640 cm-1. The monotonic peak intensity change was not as obvious as that of
the –CH2- stretch mode, probably because of the relatively low concentration of the
polyamides (16%).
It’s worth mentioning that in addition to
intensity analysis shown in the figures, the
AIMsolution software allows for various types
of analysis such as intensity ratio, peak height,
peak height ratio, peak area, peak area ratio
and purity analysis.
Figure 6. Heat map of the mode at 1640 cm-1.
over the cross section of the polymer film
sample.

All the different types of analysis can be conveniently edited within the AIMsolution
software. These analysis features and the high sensitivity of the liquid nitrogen cooled
MCT detector make the AIM-9000 FTIR microscope an ideal tool in the investigation
of the cross section of polymer films.
Figure 7. IR mode at about 1640 cm-
1 over the cross section of the
sample. Intensity increase was
observed from the lower side to the
upper side of the sample.

Conclusion
 Shimadzu’s IRTracer-100 FTIR spectrophotometer combined with the AIM-9000 FTIR
microscope can be used to analyze the layered structure of composite films.
 The microscope system allowed measurement in the transmission, reflection and ATR
modes.
 Sample preparation played an important role in the successful investigation of the film’s cross
section.
 The AIMsolution software with the optional mapping software proved an indispensable tool in
the cross section analysis.
 Experimental parameter setup proved equally essential in achieving satisfactory results.
Even with the high sensitivity of the liquid nitrogen cooled MCT detector, it might have been
difficult to obtain meaningful FTIR spectra had we not carefully selected the proper aperture
dimension.
 Sampling, measurement and analysis were easily achieved with software control. Chemical
composition variation was observed with spatial resolution of sub-10 microns level on the
cross section of film samples.
• Application News No. FTIR-1901, Characterization of Polymer Film Cross Section Using the Shimadzu
AIM-9000 FTIR Microscope (Shimadzu Scientific Instruments, Columbia, MD, December, 2018).
Reference

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