Interface quartz/electrolyte

Nechaev, E.A. and Romanov, V.P, Mobility of the electric double-layer ions at the quartz-electrolyte solution interface, Kolloid. Zh., 36, 1095, 1974. 

Previously, we have proposed that SFG intensity due to interfacial water at quartz/ water interfaces reflects the number of oriented water molecules within the electric double layer and, in turn, the double layer thickness based on the p H dependence of the SFG intensity [10] and a linear relation between the SFG intensity and (ionic strength) [12]. In the case of the Pt/electrolyte solution interface the drop in the potential profile in the vicinity ofelectrode become precipitous as the electrode becomes more highly charged. Thus, the ordered water layer in the vicinity of the electrode surface becomes thiimer as the electrode is more highly charged. Since the number of ordered water molecules becomes smaller, the SFG intensity should become weaker at potentials away from the pzc. This is contrary to the experimental result. 

Nihonyanagi, S., Ye, S. and Uosaki, K. (2001) Sum frequency generation study on the molecular structures at the interfaces between quartz modified with amino-terminated self-assemhled monolayer and electrolyte solutions of various pH and ionic strength. Electrochim. Acta, 46, 3057—3061. 

The question of the ( -potential value at the electrolyte solution/air interface in the absence of a surfactant in the solution is very important. It can be considered a priori that it is not possible to obtain a foam film without a surfactant. In the consideration of the kinetics of thinning of microscopic horizontal foam films (Section 3.2) a necessary condition, according to Reynolds relation, is the adsorption of a surfactant at both film surfaces. A unique experiment has been performed [186] in which an equilibrium microscopic horizontal foam film (r = 100 pm) was obtained under very special conditions. A quartz measuring cell was employed. The solutions were prepared in quartz vessels which were purified from surface impurities by a specially developed technique. The strong effect of the surfactant on the rate of thinning and the initial film thickness permitted to control the solution purity with respect to surfactant traces. Hence, an equilibrium thick film with initial thickness of about 120 nm was produced (in the ideal case such a film should be obtained right away). Due to the small film size it was possible to produce thick (100 - 80 nm) equilibrium films without a surfactant. In many cases it ruptured when both surfaces of the biconcave drop contacted. Only very precise procedure led to formation of an equilibrium film. 

With his model, Sverjensky (2001) predicted different distances for the adsorption of different electrolyte cations (i.e., Rb+ = 3.3 A, Sr2+ = 2.9 A) at the rutile-water interface that compared well to the distances reported from x-ray standing-wave experiments (Fenter et al., 2000). The model also suggested that trace amounts of metals (e g., Sr"" ", Ca +j other than the electrolyte cations should form inner-sphere complexes if adsorbed to the p-plane of rutile and similar sohds, and form outer-sphere complexes if adsorbed to the p-plane of quartz, goethite, and similar solids. These predictions were consistent with the results of x-ray standmg-wave and EXAFS studies (Axe et al., 1998 Fenter et al., 2000 O Day et al., 2000 Saliai et al., 2000). 

Molecular interaction with radiation is proportional to the radiation intensity, and thus to the square of the electric field vector, E 2. Equations 1-3 were used to generate Figure 2 which illustrates the variation of F 2 with z for both intrinsic and extrinsic TIRF at the quartz-aqueous electrolyte interface. Intrinsic fluorescence is more localized in the interfacial region (dp = 1040 A) than is extrinsic fluorescence using FITC (dp = 2235 A). 

The unusual nature of the silica-water system has been noted by J. A. Kitchener (7), who pointed out that the endless confusion in the literature concerning the silica-water interface has arisen because the hydration and solubility characteristics have not been understood. For example, there is the question as to why silica sols are extraordinarily stable at pH 2 where the zeta potential is zero and become increasingly sensitive to electrolytes at higher pH. where the potential is highest—in contradiction to the generally accepted electrical double layer theory. Another mystery is that crystalline quartz becomes coated with a film of amorphous silica even though the solution is undersaturated with soluble silica with respect to a surface of amorphous silica. 

Kim I-T, Egashira M, YoshimotoN, MoritaM (2011) On the electric double-layer stmcture at carbon electrode/organic electrolyte solution interface analyzed by ac impedance and electrochemical quartz-crystal microbalance responses. Electrochim Acta 56 7319-7326... 

It is important to note that determination of the width of the resonance can be critical for the use of the EQCM as a true microbalance. Relating A/ to the change in mass Am employing Eq. (17.1) is only valid if the parameter T is constant in a given composition of the solution and at constant temperature and pressure. In the general case, it may be better to regard the QCM as a quartz crystal microsensor. On the other hand, measurement of both A/ and F can be very useful in more advance analysis of the structure of the metal/electrolyte interface, employing suitable models, which can be tested experimentally. 

---