Reflection FTIR imaging measurements

Of course, most samples for microspectroscopy are not accessible for transmission measurements, particularly in those circumstances where modification of the sample occurs by preparation of a thin film. 

Fourier transform infrared microscopes are equipped with a reflection capability that can be used under these circumstances. External reflection spectroscopy (ERS) requires a flat, reflective surface, and the results are sensitive to the polarization of the incident beam as well as the angle of incidence. Additionally, the orientations of the electric dipoles in the films are important to the selection rules and the intensities of the reflected beam. In reflectance measurements, the spectra are a function of the dispersion in the refractive index and the spectra obtained are completely different from that obtained through a transmission measurement that is strongly influenced by the absorption index, k. However, a complex refractive index, n + ik can be determined through a well-known mathematical route, namely, the Kramers-Kronig analysis. 

Infrared reflection techniques are used for surface characterization because they provide highly detailed information about the molecular structure, orientation on 

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Shelton, CT, www.perkinehner.com). Samples can be measured in reflectance mode or transmission mode. Sohd samples such as biological tissues may need to be sliced into thin sections for transmission analysis. FTIR imaging can be performed on a wide variety of sample matrices, including polymers, pharmaceutical tablets, fibers, and coatings. 

The chemical polymerization of Py by CAN in PU solutions leads to the formation of PU/PPy composites. The composites were characterized by Fourier transform infrared spectrophotometry-attenuated total reflectance (FTIR-ATR], dynamic mechanical analysis (DMA], thermal gravimetric analysis (TGA], differential scanning calorimetry (DSC], X-ray photoelectron spectroscopy (XPS], and SEM measurements. The absorbances of the disordered H-bonded urethane carbonyl decrease with increasing Py concentration. The fraction of the hydrogen-bonded carbonyls is increased and the melting point increases with the increase of PPy content. These indicate the incorporation of PPy into PU may cause the complex due to the intermolecular interaction between the PPy and PU. SEM images of composite nanofibers show good distribution of the second component and the composite solution is proper to form conductive composite nanofibers. 

In this chapter, we introduce the principles of the FTIR imaging method and some of the recent applications of FTIR imaging in the study of polymeric materials. This includes an introduction to the general approach of FTIR image acquisition, the transmission and attenuated total reflection (ATR) modes of measurement, the different approaches of measuring liquid and solid samples, the considerations needed to be taken in order to obtain a reliable and accurate imaging measurement and also some of the new opportunities that exist for FTIR imaging. 

Thin film nanostructures of the III-VI compound In2Se3 were obtained inside the pores (200 nm) of commercial polycarbonate membrane by automated ECALE methodology at room temperature [157], Buffered solutions with millimolar concentrations of In2(S04)3 (pH 3.0) and Se02 (pH 5.5) were used. The atomic ratio of Se/In in the deposited films was found to be 3/2. Band gaps from FTIR reflection absorption measurements were found to be 1.73 eV. AFM imaging showed that the deposits consist of 100 nm crystallites. 

Zeolite membranes are commonly characterized by SEM, XRD. TEM, EPMA, SEM-EDX, TEM-EOS, and Nitrogen adsorption are also used to study the morphology, microstructure and composition of zeolite membranes. Usually single gas permeation, mixed gas separation, pervaporation and vapor permeation are performed to evaluate the properties of zeolite membranes. Recently, some novel characterization techniques have been applied. Infrared reflectance measurement was used to characterize membrane thickness [19]. Fluorescence confocal optical microscopy was used to image the grain boundary structure of zeolite membranes [20]. FTIR-ATR method was used to characterize the T-O vibration of zeolite membranes [21],... 

Infrared synchrotron micro-spectroscopy is also an appropriate method for identifying and visualizing the existence of localized water at buried interfaces, particularly between multilayers of polymers. It was recently shown that water inclusions can be imaged at the buried interface of solid-contact-ion-selective electrodes (SC-ISEs) [22]. In this study a poly(methyl metha-crylate)-poly(decyl methacyrlate) [PMMA-PDMA] copolymer was used. Since the PMMA-PDMA copolymer is known to be water repellent and unsuitable for water sorption at measurable levels in the bulk membrane, the detection (or non-detection) of water by reflectance SR-FTIR is symbolic of the presence (or absence) of localized zones of water at the buried interface of a solid-contact ISE employing PMMA-PDMA as the sensing membrane. In fact, SR-FTIR revealed the presence of micrometer-sized inclusions of water at the gold-to-membrane interface, whereas coupling a hydrophobic solid contact of poly(3-octylthiophene 2,5-diyl) (POT) prevented the accumulation of water at the buried interface (Fig. 2) [22]. 

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