ATR FTIR imaging

Attenuated total reflection FTIR is a well-established technique for obtaining absorbance spectra of opaque samples. The mode of interaction is unique because the probing radiation is propagated in a high index-of-refraction internal reflection element (IRE). The radiation interacts with the material of interest, which is in close contact with the IRE, forming an interface across which a nonpropagating evanescent field penetrates the surface of the material of interest to a depth in the order of one wavelength of the radiation. The electric field at the interface penetrates the rarer medium in the form of an evanescent field whose amplitude decays exponentially with distance into the rarer medium. 

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Fig. 7 ATR-FTIR image showing the distribution of LDPE in the PS/LDPE blend. The imaged area is 50 x 50 xm2...

This section introduces a novel application of IR spectroscopy, namely IR imaging, and the specific sampling technique of attenuated total reflectance (ATR). FTIR imaging in ATR mode allows one to visualize the spatial distribution of different components in polymeric materials and to study directly the effect of high-pressure CO2 on this distribution. This novel approach should benefit polymer scientists studying polymer blends and their processing with SCCO2. 

Chan, K.L.A. and Kazarian, S.G. (2008) ATR-FTIR imaging of large areas using inverted prism crystals and combining imaging and mapping. Appl. Spectrosc., 62 (10), 1095-1101. 

Glassford, S.E. et al (2012) Micro ATR FTIR imaging of hanging drop protein crystallisation. Vib, Spectrosc., 63, 492 -498. 

Figure 7.5 ATR-FTIR images of a PS-PVME blend before (a and c) and during exposure to 60 bar of COj (b and d). The images (a and b) are based on the spectral band of PS, while images c and d are based on the spectral band of PVME. (e) Spectra extracted from PVME-rich (blue) and PS-rich (red) domains. Kazarian and Chan [19]. Reproduced with permission of the American Chemical Society. (See color plate section for the color representation of this figure.)...

Figure 7.6 Variable angle ATR-FTIR imaging of two polymer laminate samples. SI consists of PS-PBMA-PC-PDMA layers, while S2 consists of PS-PC-PBMA-PDMS layers. The setup of the experiment is shown on the schematic on the left and the imaging results are shown on the right. A selection of apertures can be introduced to allow only part of the IR beam with restricted angle of incidence to reach the sample. The position of the aperture determines the resultant angle of incidence of the measurement. The angle of incidence is indicated on the left of the imaging result. The has an inverse relationship to the angle of incidence, that is, 50.1° represents a shallow d, while 42.6° represents a larger d. Frosch et al. [21]. Reproduced with permission of the American Chemical Society.

Figure 7.9 Micro-ATR-FTIR images of cellulose/PHBV blends at different compositions. CeUulose/PHBV (a) 20/80, (b) 40/60, (c) 60/40, and (d) 80/20. The size of each image is ca. 63 pm X 63 pm. Hameed 2011 [32]. Reproduced with permission of Elsevier. (See color plate...

Nagle DJ, George GA, Rintoul L, Fredericks PM. Use of micro-ATR/FTIR imaging to study heterogeneous polymer oxidation by direct solvent casting onto the ATR IRE. Vib Spectrosc 2010 53 24-27. 

Our group was the first to report imaging with a diamond ATR accessory that provided a field of view of ca. 1 mm2 and the spatial resolution of ca. 15 pm without the use of an infrared microscope [18], The demonstration of the applicability of a diamond ATR accessory for FTIR imaging opened up a range of new opportunities in polymer research, from compaction of tablets [21-23] to studying phase separation in polymer blends subjected to supercritical fluids [24], This imaging approach was successfully utilised for the study of dissolution of tablets in aqueous solutions [25], We have also demonstrated macro... 

Similar to conventional FTIR measurements, FTIR imaging with FPA detector can be operated in transmission or ATR mode. 

This accessory was used to image, in situ, the phase separation of a homogeneous LCST PS/PVME (50/50 w/w) polymer blend. A homogeneous mixture was cast directly onto the diamond, which was the ATR crystal used for the measurements. The resultant FTIR images are presented in Fig. 10.8 (Section 3.2), showing the distribution of both PS and PVME, before and after exposure to 60 bar of CO2. Following exposure to CO2 it can be seen that phase separation occurs, resulting in domains of ca. 200 pm [135]. 

The ehemieal reaction of zinc dithiophosphate has been studied using in situ ATR FTIR spectroscopy as well as with imaging XPS and ToF-SIMS. In situ ATR FTIR confirms the existence of a decomposition pathway that proceeds through the elimination of alkanes under pure thermal conditions. The reaetion product is zinc polyphosphate. Under conditions of mild mechanical stress at high temperatures, as well... 

Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy imaging (SEM), and X-ray photoelectron spectroscopy (XPS). 

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