ATR imaging

Figure 8 IR-ATR images of a PA/PTFE polymer blend bright colors PTFE clusters. Left integration of 1,149 cm-1 C-F absorption. Right PCA factor plot — additional clusters appear within the white circles. (See Color Plate Section at the end of this book.)...

Figure 9 (a) FTIR ATR image of silicone oil distribution in PA/PTFE blend. Top left ... 

Infrared ATR images showed an intermediate region between COPA and EVA of about 5 pm (Figure 13). However, a clear identification of that layer as MAH-modified LLDPE was not possible due to the low MAH content. 

Figure 13 FTIR ATR image of the polymer laminate (top left IR spectrum of COPA layer bottom left IR spectrum of EVA layer). The amide I absorption of COPA (top right) and the ester absorption of EVA (bottom right) were integrated (high intensities represented in bright color). An Intermediate region of ca. 5 pm (dimension bar) is assumed to be the LLDPE-MAH layer. Image area 50 pm x 50 pm.

A simple line scan with Raman microscopy, however, clearly showed the LLDPE-MAH layer as a ca. 5-p.m broad plateau from the evaluation of three different Raman band intensities (Figure 14). In this case a simple Raman line scan obviously is the better choice for a determination of the LLDPE-MAH layer thickness, superior even to IR-ATR imaging. We used three Raman bands... 

Typically no sample preparation required. Macro-ATR imaging accessories are commercially available, while microsystems have been described in the literature.42 ATR issues include depth of penetration, intimate contact requirement and crystal properties. The original spatial distribution of chemical species may be slightly altered when pressure is applied. 

Since ATR image involved the sample being measured in contact with an ATR crystal of high refractive index, n, the spatial resolution is unproved according to Eq. 1 and 2 [18], When germanium is used as the ATR crystal, which has a refractive index of 4, the spatial resolution achieved can be improved up to four times when compared to transmission using the same optical objective. The field of view in micro ATR imaging is ca. 50 x 50 pm2. 

Everall also demonstrated the problems of quantitative ATR imaging when trying to measure the image of a sample containing hard spheres with a diameter... 

Figure 1.28 Micro-ATR images of the PMMA film on a silicon wafer shown in Figure 1.24 obtained by integrating between (a) 1 753 and 1672cm- (X , = 5.8 am) and (b) 1179 and 1090cm- = 8.8 am). Reproduced with permission from...

N.J. Everall (2007) ATR Imaging. Meeting of the Infrared and Raman Discussion Group, Sheffield, UK, April 2007. 

In an ATR imaging study, Kazarian and Chan described the behavior of polymer blends under high-pressure COj. Under these conditions and at 40 °C, initially homogeneous blends were seen to undergo a phase separation. By using this method, it was also possible to examine the influence of other gases on the material properties of polymers [17]. Likewise, in 2006, Kaun et al. demonstrated an FT-IR imaging system for the examination of a chemical reaction in a solution, and the time-resolved model reaction of formaldehyde and sulfite was also visualized [18]. 

Another field of application, especially for ATR imaging, is that of pharmaceutical formulations. Here, in 2003, Chan et al. reported the first results on macro and micro ATR imaging of pharmaceutical tablets by characterizing the spatial distribution of active ingredients and excipients [19]. Further examples in this field are described in Chapter 10 of this volume. 

The second system involved a poly (ethylene terephthalate) (PFT) film, coated with a 3-4 nm aluminum layer. By using a semiconductor laser, grooves with a width and distance of 4.8 pm were written into the sample, in the form of a grid (tesa AG) and FT-IR/ATR imaging measurements performed within the area of the grid. 

Figure 9.14 Visible image and FT-IR/ATR images of the borderline between PE and the PC/PE laminate (50x50 4m )...

Figures 9.16 and 9.17 show graphs of the integral absorbance of PE and PC (FT-IR/ATR imaging measurement) and of PC (FT-IR imaging measurement in transmission) versus pixel number of a row (64 pixels) perpendicular to the PE/PC borderline between the laminate (PE/PC) and the single layer (PE) (50 pm and 260pm, respectively). The integral absorbances used for the calculation of the spatial resolution at 95% and 5% of the maximum integral absorbance (100%) are marked.

Figure 9.18 Visible Image of a 60gm-wide grid written by a laser into an aluminum-metallized PET film (dark lines = PET) and the corresponding v(C=0) FT-IR/ATR image.

The applicability of ATR-FT-IR imaging ranges from micro ATR imaging using a microscope objective to the use of ATR accessories with focused or expanded optics, without need to use the microscope. The ATR crystal in a prism shape... 

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