Attenuated total reflectance technique

The ability to recover monolayers and subject them to meaningful analysis has become practical only in recent years because of the development of new methods of trace analysis. High-performance liquid chromatography and vapor phase chromatography allow separation and identification of such small quantities (54a). Attenuated total reflectance techniques for infrared analysis (56) and field desorption mass spectrometry (68) have been applied to the trans-... 

During this time period, several groups investigated the SH response from metallic films using attenuated total reflection techniques (ATR) in which the nonlinear response is enhanced by coupling into surface plasmons (or polaritons) [28-38]. Simon et al. [28] were the first to demonstrate this effect. 

The intense absorption of the P—O structure obscures all detail in this region. The use of single attenuated total reflection technique, coupled with scale expansion, resulted in the spectrum shown in Figure 2. The maxima in the asymmetric P—O- stretching band is readily measured. 

IR spectroscopy is a common analytical technique in the textile industry. IR is capable of identifying fibers and their additives, as well as showing quantitative blend ratios and additive contents. The ATR (attenuated total reflection) technique, especially in its multiple form, MIR (multiple internal reflection) is of special importance in this field. The sample preparation is simple and fast the cut out swatches with appropriate surface areas are placed against each side of the MIR crystal, ensuring sufficient and uniform contact across the crystal surface. The internal reflection methods are non-destructive, so that the sample may be saved for other types of analysis, they are, further, methods of surface analysis. This is advantageous in all cases where the finish resides primarily on the fiber surface. In this case, a very strong spectrum of the finish is obtained, with minimal interference from the base fiber (Hannah et al., 1975). 

Dumont and coworkers [136, 155, 156] have observed that shining doped (or functionalized) polymer thin hlms with noncentrosymmetric dipolar chromo-phores, induces a significant increase of electro-optic coefficient in the chromo-phore absorption band, corresponding to a better, polar orientation of chromo-phores. The measurements have been done by using the attenuated total reflection technique, and the optical field polarization was perpendicular to the applied low-frequency external electric field to the thin film (Fig. 33). A better stability of induced orientation was observed in the case of functionalized polymers than in guest-host system, as is usually the case with the static field poled polymers. The chromophores orient with dipolar moments perpendicular to the optical field (and parallel to the applied static (or low frequency) field. As will be discussed later, the chromophore orientation undergoes a trans-cis isomerization process (Fig. 34). 

FT-IR spectra can be obtained for proteins in aqueous solution or adsorbed onto surfaces by a combination of transmission and attenuated total reflectance techniques. 

Neivandt, D. J., Gee, M. L., Tripp, C. P, Hair, M. L. (1997) Coadsorption of poly(styrenesulfonate) and cetyltrimethylammonium bromide on silica investigated by attenuated total reflection techniques. Langmuir 13,2519-2526. 

Zhu Y, Uchida H, Watanabe M. Oxidation of carbon monoxide at a platinum film electrode studied by Fourier transform infrared spectroscopy with attenuated total reflection technique. Langmuir 1999 15 8757-64. 

The infrared spectrum was determined by the attenuated total reflectance technique (ATR) on the fracture surface of a sample of a typical example of the adhesive in question, exposed in the 60 C, 100% R.H. cabinet for 40 days. Figure 1 shows absorption in the -OH region, 3400 cm l, attributable to water, relative to the unexposed control. These samples, dried (Figure 2), show no significant changes except removal of the water. The results are summarized in Table 2 as absorbance ratios, relative to an internal standard, the absorbance at 1180 cm l. The major change is a decrease in -OH absorption. Other changes in ratio are well within experimental error by the technique. 

Fourier transform infrared spectroscopy (FTIR) was conducted with a Spectmm 100 FTIR Spectrometer Perkin Elmer (Japan). FTIR spectra were recorded in range of 4000 to 550 cm with 4 cm resolution by using an attenuated total reflectance technique (Chittur, 1998). 

A number of methods have been used to measure the EO coefficients and ni of the poled polymer samples. These EO measurements are made by detecting the change in refractive index of the poled polymer sample when a modulating electric field is applied to the sample. Mach-Zehnder [42,43]. Fabry-Perot [44,45], and Mich-elson [46] interferometric techniques have been used to evaluate the EO coefficients. Other techniques, such as an attenuated total reflection technique [47,48] and an ellipsometric technique [49-51], have also been employed to determine the r coefficients. 

Raman spectroscopy has a definite advantage for biological systems in that absorption bands due to water do not present a problem. However, fluorescence may present a major problem for some samples when examined by Raman techniques and photochemical interactions may need to be borne in mind. The use of horizontal attenuated total reflectance techniques has become more popular for the study of aqueous solutions of biological samples. 

The appearance of surface defects in animal furs is another reported application of attenuated total reflectance techniques. Figure 4 shows an example of a valuable fur damaged by white spots. The manufacturer claimed that the client was responsible for damage to the fur because it had been stored in an inappropriate environment or because of treatments it had been exposed to. The client, on the other hand, claimed its original treatment during manufacture was to blame. Infrared analysis demonstrated that the white spots came from the migration of animal fat to the surface and bands were comparable to the fat extracted from the natural fur. Other substances, such as silicone, have been found in this kind of sample. 

The development of repellent finishing is benefiting from recent progress in surface analyses by electron spectroscopy for chemical analyses, scanning electron microscopy, and the attenuated total reflection technique of infrared spectroscopy. 

The attenuated total reflection technique, in which the sample is brought into good optical contact with a surface at which the infrared radiation undergoes total reflection, gives spectra similar to, but not identical with, absorption spectra (Fahrenfort and Visser [1962]). This technique gives excellent spectra for powdered minerals (Harrick and Riederman [1965]). 

The attenuated total reflectance (ATR) technique is used commonly in the near-infrared for obtaining absorption spectra of thin Aims and opaque materials. The sample, of refractive index i, is placed in direct contact with a material which is transparent in the region of interest, such as thallium bromide/thallium iodide (known as KRS-5), silver chloride or germanium, of relatively high refractive index so that Then, as Figure 3.f8... 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

For on-bead analysis vibrational spectroscopy (IR-spectroscopy) can be employed attenuated total reflection is a method allowing fast and nondestructive on-bead analysis of small samples (single bead analysis) without significant sample preparation. Solid phase NMR is the method of choice if complex structural analysis is intended on the support. Spatially resolved analysis on the resin is possible with microscopic techniques. 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

Surface composition and morphology of copolymeric systems and blends are usually studied by contact angle (wettability) and surface tension measurements and more recently by x-ray photoelectron spectroscopy (XPS or ESCA). Other techniques that are also used include surface sensitive FT-IR (e.g., Attenuated Total Reflectance, ATR, and Diffuse Reflectance, DR) and EDAX. Due to the nature of each of these techniques, they provide information on varying surface thicknesses, ranging from 5 to 50 A (contact angle and ESCA) to 20,000-30,000 A (ATR-IR and EDAX). Therefore, they can be used together to complement each other in studying the depth profiles of polymer surfaces. 

A number of techniques have been employed that are capable of giving information about amorphous phases. These include infrared spectroscopy, especially the use of the attenuated total reflection (ATR) or Fourier transform (FT) techniques. They also include electron probe microanalysis, scanning electron microscopy, and nuclear magnetic resonance (NMR) spectroscopy. Nor are wet chemical methods to be neglected for they, too, form part of the armoury of methods that have been used to elucidate the chemistry and microstructure of these materials. 

It is generally assumed the fluorescence and Fourier transform mid-infrared (FT-IR) spectroscopies do not suffer from the above-mentioned inconveniences and may be applied to turbid samples. Front-face (fluorescence) and attenuated total reflection (FT-IR) techniques may provide information on the structure of adsorbed proteins. 

FTIR instrumentation is mature. A typical routine mid-IR spectrometer has KBr optics, best resolution of around 1cm-1, and a room temperature DTGS detector. Noise levels below 0.1 % T peak-to-peak can be achieved in a few seconds. The sample compartment will accommodate a variety of sampling accessories such as those for ATR (attenuated total reflection) and diffuse reflection. At present, IR spectra can be obtained with fast and very fast FTIR interferometers with microscopes, in reflection and microreflection, in diffusion, at very low or very high temperatures, in dilute solutions, etc. Hyphenated IR techniques such as PyFTIR, TG-FTIR, GC-FTIR, HPLC-FTIR and SEC-FTIR (Chapter 7) can simplify many problems and streamline the selection process by doing multiple analyses with one sampling. Solvent absorbance limits flow-through IR spectroscopy cells so as to make them impractical for polymer analysis. Advanced FTIR... 

For solid-phase samples or for membrane interaction studies, it can be very useful to use the alternative sampling technique of attenuated total reflectance (ATR). Films or solutions can be placed on a specially... 

In materials investigations surface-sensitive techniques are of special interest. The major contribution of infrared spectroscopy to this field is internal reflection spectroscopy (IRS), often called the "attenuated total reflection" (ATR) technique. To describe theory and principle, electromagnetic wave theory must be apphed [33]. 

Internal reflectance (attenuated total reflectance ATR ). The internal reflectance or, more usually, attenuated total reflectance (ATR), technique depends on the total reflectance of an IR beam at the internal face of an IR-transparent crystal of high IR refractive index, as shown in Figure 2.38. Medium 1 is a prism of such a material (for example, Si, Ge or KRS-5 [thallous bromide- iodide]), medium 2 is a thin coating of a metal (Au, Pt, Fe) which forms the working electrode and medium 3 is the electrolyte. The... 

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