Liquid cells

Several designs for STM electrochemical cells have appeared in the literature [M]- hr addition to an airtight liquid cell and the tip insulation mentioned above, other desirable features include the incorporation of a reference electrode (e.g. Ag/AgCl in saturated KCl) and a bipotentiostat arrangement, which allows the independent control of the two working electrodes (i.e. tip and substrate) [ ] (figure BL19.11). 

As with STM, the AFM can be operated in air, in vacuum or under liquids, providing a suitable cell is provided. Liquid cells (figure Bl.19.20) are particularly usefiil for the examination ofbiological samples. 

The direct transmission experiment is the most elegant and yields the most quantifiable results. The beam makes a single pass through the sample before reaching the detector. The bands of interest in the absorbance spectrum should have peak absorbances in the range of 0.1—2.0 for routine work, although much weaker or stronger bands can be studied. Various holders, pellet presses, and liquid cells have been... 

In contrast to many other surface analytical techniques, like e. g. scanning electron microscopy, AFM does not require vacuum. Therefore, it can be operated under ambient conditions which enables direct observation of processes at solid-gas and solid-liquid interfaces. The latter can be accomplished by means of a liquid cell which is schematically shown in Fig. 5.6. The cell is formed by the sample at the bottom, a glass cover - holding the cantilever - at the top, and a silicone o-ring seal between. Studies with such a liquid cell can also be performed under potential control which opens up valuable opportunities for electrochemistry [5.11, 5.12]. Moreover, imaging under liquids opens up the possibility to protect sensitive surfaces by in-situ preparation and imaging under an inert fluid [5.13]. 

Fig. 5.6. Cross-sectional view of a liquid cell for in-situ AFM measurements of surface processes.

FIGURE 14.17 A diaphragm cell tor the electrolytic production of sodium hydroxide from brine (aqueous sodium chloride solution), represented by the blue color. The diaphragm (gold color) prevents the chlorine produced at the titanium anodes from mixing with the hydrogen and the sodium hydroxide formed at the steel cathodes. The liquid (cell liquor) is drawn off and the water is partly evaporated. The unconverted sodium chloride crystallizes, leaving the sodium hydroxide dissolved in the cell liquor. 

Practically all liquid cells with reversible interfacial equilibria examined can be considered as liquid galvanic cells of the Nernst, Haber, or intermediate type [3]. Usually, a dashed vertical bar ( ) is used to represent the junction between liquids. A double dashed vertical bar ( ) represents a liquid junction in which the diffusion potential has been assumed to be eliminated. 

Liquid cells containing an ion exchanger in the organic phase, e.g., a salt with a highly hydrophobic anion or cation R, could be considered [3] as concentration cells ... 

Cells of the type in Scheme 10 represent the simplest case of an ion-selective liquid cell its EMF is often called a membrane, or monoionic, potential [3]. The first term is too narrow due to the fact that the membrane potential corresponds to the behavior of a number of cells, including those of Schemes 8 to 11, and to the cells with solid membranes and with Donnan equilibrium. 

Solutions Fixed-path length liquid cell with KBr windows Wick cell Best for low-viscosity liquids For small volumes of liquid (1 ptL)... 

At about the same time, Matsushita et al. reported a study of quasi-two-dimensional deposition in a thin layer of electrolyte solution [3], A binary zinc sulfate solution was confined within a planar disk, 17 cm in diameter, bounded on the bottom by a glass plate and on the top by a layer of immiscible organic liquid. Cell potentials of several volts were applied, and the deposits grew along the liquid-liquid interface. In this cell, the depth of solution was 10 cm, but the deposit formed only along the interface between the electrolyte solution and the organic layer. Since a... 

The growth mechanisms of two typical materials, ZnS and PbS, have been studied by AFM by both in situ and ex situ techniques.91013-17 An AFM liquid cell was used for the in situ studies for comparison with films grown with the SILAR equipment. 

Transmission Fourier transform infrared (FTIR) spectroscopy, 24 72, 110 Transmission liquid cells, types of,... 

Figure 10.17—Cells used for mid IR spectroscopy, a) Gas cell with direct optical path (reproduced with permission of Wilmad) b) expanded view of a liquid cell with a fixed path-length (from Eurolabo document).

Manganese dioxide is a cheap, readily available material which is used worldwide as a solid cathode for primary liquid cells. During recent years,... 

For routine use liquid cells are of two types (a) the demountable cells in which the path length may be varied by utilising spacers of lead or Teflon of appropriate thickness these cells have the advantage that they may be easily dismantled after use for cleaning and if necessary for repolishing of the cell win-... 

The most accurate way of compensating for solvent absorption is to use the more expensive variable path length cells (Fig. 3.7) in which one of the plates which constitute the liquid cell can be moved with the aid of a micrometer device to allow adjustment to any required path length. This allows the accurate matching in the spectrophotometer of two such cells filled with the appropriate solvent. One cell may then be emptied, cleaned and refilled with solution so that the spectrum of the solute may be recorded. 

All experiments utilized a variable wavelength uv detector. Analysis of the hexane fraction was carried out using both the UV detector and an on-line Nicolet 6000 FTIR. The FTIR flow cell interface has been described in detail elsewhere.(9) This same FTIR was also used to gather static spectra on the various fractions, utilizing a liquid cell with KBr windows. 

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