Attenuated total reflectance, interfacial

In the various sections of this chapter, I will briefly describe the major characteristics of FT-IR, and then relate the importance of these characteristics to physiochemical studies of colloids and interfaces. This book is divided into two major areas studies of "bulk" colloidal aggregates such as micelles, surfactant gels and bilayers and studies of interfacial phenomena such as surfactant and polymer adsorption at the solid-liquid interface. This review will follow the same organization. A separate overview chapter addresses the details of the study of interfaces via the attenuated total reflection (ATR) and grazing angle reflection techniques. 

The application of FT-IR to a wide variety of interfacial phenomena is possible using either attenuated total reflectance (ATR) or grazing angle reflection -absorption. The details of these optical techniques are discussed in a subsequent chapter, in the context of characterization of Langmuir - Blodgett films and self-assembled mono and multilayers. However, ATR has been applied in a number of other areas which will be mentioned here. 

Evaluation of the meaningfulness of results from less sensitive and less selective methods needs additional attention (e.g. attenuated total reflectance infrared (ATR-IR) or solid-state NMR spectrometry) [2]. Indirect insights from functional studies include support for transmembrane orientation (Fig. 11.13b) from parabolic dependence of the activity of synthetic ion channel or pore on bilayer thickness (Section 11.3.7) [56] and other readouts in support of operational hydrophobic matching. Flippase activity may provide some support for interfacial location (Section 11.3.7, Fig. 11.13d) [61, 62]. 

Specific interactions in binary blends of ethylene-vinyl acetate copolymer with various low molecular weight terpene-phenol tackifying resins (TPR) were systematically investigated, as a function of the composition of the blend and of the electron acceptor ability of the resin, by using attenuated total reflection FTIR spectroscopy. Molecular acid-base were evidenced between TPR hydroxyl groups and EVA carbonyl groups. Quantitative information on the fraction of acid-base bonded entities, the enthalpy and equilibrium constant of pair formation were obtained. A crystalline transition of the EVA copolymer was observed and discussed in terms of enthalpy and entropy considerations based on FTIR and calorimetric DSC investigations. Fundamental results are then summarised to predict the interfacial reactivity of such polymer blends towards acid or basic substrates. 16 refs. 

Electron spectroscopy for chemical analysis (ESCA) [9] and Fourier transform infrared (FTIR) spectroscopy [10] with attenuated total reflectance (ATR) can also be used for routine surface studies. FTIR spectroscopy is known to have the sensitivity to determine the average orientation and reorientation of interfacial chains. But it does not directly provide information on the motion itself. The mobility of a solute in the neighborhood of an alkyl chain can be measured by fluorescence spectroscopy [11]. 

Urban [7] studied the quantitative aspects of alternated total reflectance and photoaconstic step-scan FT-IR and interfacial analysis of polymeric films. There are significant implications arising from the ability to stratify polymer surfaces and interfaces using attenuated total reflectance (ATR) and photoacoustic step-scan FT-IR spectroscopy. Theoretical concepts and... 

The use of evanescent waves is very valuable to the study of interfacial properties. Techniques such as total internal reflection fluorescence (TIRF) and attenuated transmitted reflectance (ATR) use the energy of evanescent waves to probe thin regions in the vicinity of an interface to determine surface concentrations of interfacial species. 

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