Dissociation field effect

The conductivity also increases in solutions of weak electrolytes. This second Wien effect (or field dissociation effect) is a result of the effect of the electric field on the dissociation equilibria in weak electrolytes. For example, from a kinetic point of view, the equilibrium between a weak acid HA, its anion A" and the oxonium ion H30+ has a dynamic character ... 

At high field strengths a conductance Increase Is observed both In solution of strong and weak electrolytes. The phenomena were discovered by M. Wien (6- ) and are known as the first and the second Wien effect, respectively. The first Wien effect Is completely explained as an Increase In Ionic mobility which Is a consequency of the Inability of the fast moving Ions to build up an Ionic atmosphere (8). This mobility Increase may also be observed In solution of weak electrolytes but since the second Wien effect Is a much more pronounced effect we must Invoke another explanation, l.e. an Increase In free charge-carriers. The second Wien effect Is therefore a shift in Ionic equilibrium towards free ions upon the application of an electric field and is therefore also known as the Field Dissociation Effect (FDE). Only the smallness of the field dissociation effect safeguards the use of conductance techniques for the study of Ionization equilibria. 

Before proceeding to a complete calculation relating the conductance Increase to the amplitude of the field dissociation effect and Its temporal behavior we will give a short description of the actual circuit used for the field modulation technique (Figure 1) with reference to the previous discussion. 

Field factor of the field dissociation effect Small change... 

Therefore the actual field dissociation effect (or second Wien effect) as a whole is also determined by the dipole moment of the ion pair which can dissociate into the free ions. 

Honda, T., Evereart, J., and Persoons, A., 1979, Dependence of the field dissociation effect on electric field strength, in "Non-linear behaviour of Molecules, Atoms and Ions in Electric, Magnetic or Electromagnetic Fields, L. Neel, ed., Elsevier, Amsterdam. 

Persoons, A., 1974, Field dissociation effect and chemical relaxation in electrolyte solutions of low polarity, J. Phys. Chem., 78 1210. 

Figure 19. Field dissociation effect as a function of the field strength for solution of tetrabutylammonium picrate (TBAP) in diphenyl ether measured at different frequencies. 3.9xl0 M TBAP, 40 kHz, 1.5 X 10" M TBAP, 40 kHz, 3.9 x 10" M TBAP, 100 kHz. (After Ref. 55.)...

Figure 20. Field dissociation effect for high electric field strength for potassium ferricyanide solution. (After Ref. 52.)...

The reason that a compound ion can be field dissociated can be easily understood from a potential energy diagram as shown in Fig. 2.23. When r is in the same direction as F, the potential energy curve with respect to the center of mass, V(rn) is reduced by the field. Thus the potential barrier width is now finite, and the vibrating particles can dissociate from one another by quantum mechanical tunneling effect. Rigorously speaking, it... 

Fig. 2.26 When 4He is replaced with 3He, the secondary Rh2+ peak disappears even though 3HeRh2+ ions are still formed. At first glance, this strong isotope effect is most surprising since one would expect 3HeRh2+ to field dissociate more easily than 4HeRh2+ because of its smaller reduced mass. This peculiar isotope effect is the result of a center of mass transformation in the applied field, as can be understood from the Schroedinger equation of eq. (2.63), already explained in...

In the styrene (MJ-indene (Mz) system, rx increased with the field. This result shows that the dissociation of ion pairs at the growing chain ends, the terminal group of which is styrene, was enhanced by the field. As was mentioned above, the field has no effect on the homopolymerization of styrene by boron trifluoride etherate in nitrobenzene (see Fig. 5). This result of the homopolymerization seems to be inconsistent with that obtained for the copolymerization, but can be accounted for as follows. The field-accelerating effect decreases as kp/kp decreases, when an enhancement of the degree of dissociation with the electric field is given. The fact that no field effect was observed on the homopolymerization of styrene with boron trifluoride etherate in nitrobenzene may be attributed to a fairly small value of kp/kp, in addition to the factor af 1. On the other hand, the field enhanced the polymerization of indene by boron trifluoride etherate in nitrobenzene (16). The difference in the field effects of the two monomer systems suggests that the following relation must hold, ... 

We condude this section by stating that the field-accelerating effect on copolymerizations and the change of the monomer reactivity ratio with the field can be accounted for in terms of the interpretation proposed for cationic homopolymerizations, namely the field-facilitated dissociation of the growing chain ends. We should note that the observed field influence on the copolymerization excludes the possibility of the electroinitiated polymerization mechanism. 

To see the magnetic field s effect on the chemical bond of H2, the dissociation energy (Table 13.3), quadrupole moments (Table 13.4), and the electron density under various strengths of parallel and perpendicular magnetic fields (Fig. 13.2) were calculated. Our results here are basically in agreement with previous studies on H2+ in a magnetic field [18,22,25,32]. Here, we briefly summarize our results ... 

As shown in Figure 10.24, the conductance exceeds this maximum value considerably when the field exceeds about 5 kV/cm. An early explanation involved some kind of Wien effect. The first Wien effect is due to the liberation of ions from the counterion cloud around charged particles such as proteins, whereas the second one describes the creation of new charge carriers by field dissociation of week electroljrtes. Both of these effects together can explain a conductivity increase by several percent but not by 40% as seen in Figure 9.24. Moreover, this dramatic conductivity increase is only found in solution containing aggregated amphiphiles like lipids. 

Applications of Raman to polymer/additive deformulation are still rather few, especially if compared to IR methods (cfr. Chp. 1.2.1). Hummel [108] has attributed the general lack of applications of RS in the field of plastics additives to poor Raman scattering of certain substance categories, unsatisfactory reproducibility of the spectra and scarcity of specific Raman libraries [385,386]. Polymer/additive analysis by means of Raman spectroscopy is mainly restricted to fillers, pigments and dyes the major usefulness comes from NIR FT-Raman, which greatly overcomes the fluorescence problem. The ion-pair dissociation effect of the 2-keto-4-(2,5,8,11-tetraoxadodecyl)-l,3-dioxolane modified carbonate (MC3) plasticiser in poly(ethylene oxide) (PEO) was studied by means of Raman, FTIR and EX-AFS [387]. Another study established the feasibility of using Raman spectroscopy to quantify levels of melamine and melamine cyanurate in nylons [388]. 

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