Surface relaxation spectrometry

Relations (5.275), (5.276) can be used for the interpretation of experimental results obtained by surface relaxation spectrometry methods, for example, by the capillary wave method. 

Kakorin, S. and Neumann, E. (2002) Electrooptical relaxation spectrometry of membrane electroporation in lipid vesicles. Colloids and Surfaces A, IW (2-3), 147-165. 

Among various relaxation spectrometry methods of liquid surface layers the transverse capillary waves has been used most frequently for micellar solutions [96 - 101]. The shape of the concentration dependence of the wavelength is the same for all investigated cationic, anionic and nonionic surfactants and resembles the corresponding dependence of surface tension. Figure 16 shows as an example the experimental results for solutions of SDS [96]. 

To our knowledge, this is the first study of the relaxations of an oxide surface by GIXS, and the first experimental determination of the relaxation and termination of the a-Al203(0001) surface. Another determination has been performed very recently by combining time-of-flight scattering and recoiling spectrometry with LEED and classical ion trajectory simulations [59], with essentially the same results. 

Calculations for unreconstructed AgBr (100) surfaces indicate that surface rumpling occurs as halide ions relax outwards and silver ions move in toward the bulk [35]. The results of fluorescence SEXAFS measurements are consistent with the presence of such surface rumpling [47]. The calculations also indicate that rumpling is enhanced by the presence of iodide at the surface and that surface iodide ions have a marked propensity to cluster. These predictions are consistent with the observation of enhanced iodide concentrations at surfaces in AgBr, yIy thin films and emulsion grains, as measured by secondary ion mass spectrometry and ion scattering spectrometry [48,49]. 

Delville and co-workers selected 20 nm Si02 and 13 nm AI2O3 from commercial sources as particulate substrates for the attachment of aminopropyltrimethoxysilyl (APS) GdDTPA. The derivatized particles were prepared either by amination followed by reaction with DTPA bis(anhydride), or by peptide coupling of the particle surface amines with DTPA. The grafting of APS on sUica, as monitored by DRIFTS, resulted in the disappearance of Si-OH bands, and the appearance of the expected CH2 and carbonyl peaks of DTPA. XPS data established that Gd constituted about 4 atom % of silica, and 2 atom % of AI2O3. In this system there arc approximately 4 Gd complexes per silica particle as determined by inductively coupled plasma (ICP) mass spectrometry, with an average relaxivity. 

Liquids are one of the easiest classes of materials to study quantitatively via single- or multi-reflection ATR because a well-defined contact surface is obtained. The particular advantage of ATR over conventional transmission for the study of liquids is that the requirements on the liquid cell can be relaxed, especially where small thicknesses are required for transmission measurements. Simpson [97] used HATR-FTIR for the multicomponent analysis of formulated oils. Internal reflection spectrometry can also be used to identify solutes in volatile solvents since the solvent can be readily evaporated, leaving the solute as a thin layer on the surface of the IRE. Repetitive analysis of liquid samples is made easy by the wipe on/wipe off sampling afforded by the horizontal ATR accessory. Table 1.14 lists the preferred accessories for various solid sample types. When both single-bounce and multi-bounce are indicated, single-bounce is more suitable for examining the main component multi-bounce qualifies for lower concentration components or weaker spectral features. 

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