Molecular capacitor

Unlike the rest of the chapter, here we adopt Gaussian electrostatic units which are typically used in the literature devoted to molecular capacitors and double layer theory. 

In the analysis of molecular capacitors, the diffuse layer and elastic capacitors, we have always assumed that the electrode charge density a could be controlled. Under such conditions it is generally possible for C to become negative while the system remains stable. For example, contraction of the gap z in an elastic capacitor proceeds smoothly with cr growing until the plates come in contact, while C becomes negative for z < 2/3. At the same time, as shown in Section II for an EC connected to a battery, the EC collapses after z 0.6 is reached. How can these seemingly contradictory results be reconciled And how can cr-control be related to reality Is C < 0 observable These questions are addressed in this section. 

Chen G, Bandow S, Margine ER, Nisoli C, Kolmogorov AN, Crespi VH, Gupta R, Sumanasekera GU, Iijima S, Eklund PC (2003) Chemically doped double-walled carbon nanotubes cylindrical molecular capacitors. Phys Rev Lett 27 257403... 

G. Chen, S. Bandow, E. R. Margine, C. Nisoli, A. N. Kolmogorov, V. H. Crespi, R. Gupta, G. U. Sumanasekera, S. Iijima, and P. C. Eklund, Chemically doped double-walled carbon nanotubes cylindrical molecular capacitors, Phys. Rev. Lett. 90(25), 257403-1-4 (2003). 

The interfacial region of a metal up to the IHP has been considered as an electronic molecular capacitor, and this model has explained many experimental results with success20. Another important model is the jellium model21 (Fig. 3.13fo). From an experimental point of view, the development of in situ infrared and Raman spectroscopic techniques (Chapter 12) to observe the structure, and the calculation of the bond strength at the electrode surface can better elucidate the organization of the double layer. Other surface analytical techniques such as EXAFS are also valuable. 

The adsorbed Stem layer is compensated by a compact and essentially fixed layer of hydrated counterions and water molecules which takes the form of a molecular capacitor between the inner and outer Helmholtz planes shown in Figure 9.14. The solid surface adsorbs the Stem layer ions and gives a potential of the inner Helmholtz plane, which is partially compensated by the hydrated counterions and water molecviles of the outer Helmholtz plane. The diffuse double layer of (jOuy-Chapman starts at the OHP and extends further into the liquid. 

The double layer can be thought of as a molecular capacitor, where one plate is represented by the charges in the metal and the other plate by the ions at a minimum distance in the solution. The distance between the plates is of molecular dimensions... 

FIGURE 5.2. Classic models of the interface for charged surfaces include, (a) the early Helmholtz model of a molecular capacitor, (b) the Gouy-Chapman model of the diffuse double layer, and (c) the Stem model. 

Figure 14 Sketch of a molecular capacitor of thickness d at a spherical interface, which can be formed either by adsorbed zwitterionic surfactant or by charged surfactant head groups and their counterions the Gibbs dividing surface of radius a is chosen to be the boundary between the aqueous...

This component is normally described in terms of a molecular capacitor modei. According to this description, the electrode is covered with a monolayer of solvent molecules. The electrolyte ions are essentially excluded from this layer, except when strong chemical interactions result... 

Since e > eo, we seek to explain the smaller field in the presence of the dielectric in terms of molecular properties and the way in which they are affected by the electric field. An easy way to visualize the effect is to picture an opposing surface charge-indicated as in Fig. 10.4b—accumulating on the dielectric. This partially offsets the charge on the capacitor plates to a net charge density a - so that Eq becomes E and is given by... 

Sulfur hexafluoride [2551-62-4] 6 molecular weight 146.07, is a colorless, odorless, tasteless gas. It is not flammable and not particularly reactive. Its high chemical stabiUty and excellent electrical characteristics have led to widespread use in various kinds of electrical and electronic equipment such as circuit breakers, capacitors, transformers, microwave components, etc (see Electronic materials). Other properties of the gas have led to limited usage in a variety of unique appHcations ranging from medical appHcations to space research. 

Electrically, the electrical double layer may be viewed as a capacitor with the charges separated by a distance of the order of molecular dimensions. The measured capacitance ranges from about two to several hundred microfarads per square centimeter depending on the stmcture of the double layer, the potential, and the composition of the electrode materials. Figure 4 illustrates the behavior of the capacitance and potential for a mercury electrode where the double layer capacitance is about 16 p.F/cm when cations occupy the OHP and about 38 p.F/cm when anions occupy the IHP. The behavior of other electrode materials is judged to be similar. 

The use of inadiation or electron bombardment offers an alternative approach to molecular dissociation to the use of elevated temperamres, and offers a number of practical advantages. Intensive sources of radiation in the visible and near-visible are produced by flash photolysis, in which a bank of electrical capacitors is discharged tlrrough an inert gas such as ktypton to produce up to 10 joule for a period of about 10 " s, or by the use of high power laser beams (Eastham, 1986 (loc.cit.)). A more sustainable source of radiation is obtained from electrical discharge devices usually incorporating... 

An alternative method of studying the molecular motions of a polymeric chain is to measure the complex permitivity of the sample, mounted as dielectric of a capacitor and subjected to a sinusoidal voltage, which produces polarization of the sample macromolecules. The storage and loss factor of the complex permitivity are related to the dipolar orientations and the corresponding motional processes. The application of the dielectric thermal analysis (DETA) is obviously limited to macromolecules possessing heteroatomic dipoles but, on the other hand, it allows a range of frequency measurement much wider than DMTA and its theoretical foundations are better established. 

Capacitors made of high-surface carbon with PVdF-co-HFP as a binder and filled with neat ionic liquids, without any molecular solvent, show high specific capacity, up to 180 F/g [13],... 

Among the two-terminal devices that can be imagined for UE [capacitors, inductors, rectifiers, negative differential resistance (NDR) devices], the simplest is a molecular wire, that is, a molecule capable of conducting electricity a nanoconductor or, equivalently, a nanoresistor. Even the most conductive of molecular wires has a minimum resistance. 

Polychlorinated biphenyls (PCBs) were manufactured by catalytic chlorination of biphenyl to produce complex mixtures, each containing 60-90 different PCB molecular species or congeners (see Chaps. 1 and 4). In the United States, PCB mixtures were manufactured by Monsanto under the trade name Aroclor and were widely used as dielectric fluids in capacitors and transformers from 1929 to 1978. PCBs are widespread contaminants of aquatic sediments and continue to be a focus of environmental concern because they tend to accumulate in biota and are potentially toxic. The following sections show the most effective bioremediation techniques applied to various PCB contaminated environments ... 

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