Interfacial reflection spectrometry

From the beginning of the 1980s, some effective experimental approaches based on new principles have been invented for the study of interfacial reactions in solvent extraction chemistry. Recently, some methods were developed from our laboratory, the highspeed stirring (HSS) method [4,5], the two-phase stopped flow method [6], the capillary plate method [7], the reflection spectrometry [8], and the centrifugal liquid membrane (CLM) method [9]. 

FIGURE 2.15 Schematic drawing of the simple optical modification of a fluorescence cell for the measurement of the interfacial concentration using reflection spectrometry. 

Fig. 3. Total internal reflection cell used for the interfacial fluorescence lifetime measurement (left) and the external reflection absorption spectrometry (right).

For all these specialty polymers, deuterium can be used as a label on one or the other monomer. Deuterium labeling allows the use of techniques based on ion detection such as forward recoil spectrometry (FRES), nuclear reaction analysis (NRA) or secondary ion mass spectrometry (SIMS). If a high-resolution depth profile of the interfacial region is needed, neutron reflectivity can also be used. The main drawback of that approach is the cost of the deuterated polymers while deuterated styrene and methyl methacrylate are expensive but commercially available, other monomers need to be synthesized and the cost can be quite prohibitive. 

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]. 

Nowadays, the use of the reflection electron microscope (REM) or, recently, the tunnel electron microscope, as well as secondary ion mass spectrometry (SIMS), AES, electron-dispersive X-ray spectrometry, impedance spectroscopy, and so on, are yielding substantial increases in the knowledge of corrosion reactions in coatings and at their interface with metal or other substrates. As far as zinc or zinc-coated surfaces are concerned, problems of interfacial and intercoat adhesion, differential diffusion phenomena and electrolytic cell behavior on the substrate, and interreactions of zinc with conversion coatings (chromates, phosphates, silanes, silanols, etc.) have been analyzed, leading toward spectacular improvements in, for example, paint adhesion, absorption of conversion coatings and, in general, the protective action inside films as well as on their substrates. 

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