Counterion/cation effect

The counterion/cation effect choice of electrolyte The monomer Chemical polymerization The quest for extra functionality Molecular Structure and Microstructure of Polypyrrole Molecular Weight, Branching and Crosslinking Crystallinity and Molecular Order Surface Morphology and Film Density References... 

The ion transport number is defined as the fraction of current carried through the membrane by counterions. If the concentration of fixed charges in the membrane is high compared to the concentration of the ambient solution, then the mobile ions in the IX membrane are mosdy counterions, co-ions are effectively excluded, and the ion transport number then approaches 1. Commercial membranes have ion transport numbers in dilute solutions of ca 0.85—0.95. The relationship between ion transport number and current efficiency is shown in Figure 3 where is the fraction of current carried by the counterions (anions) through the AX membrane and is the fraction of current carried by the counterions (cations) through the CX membrane. The remainder of the current (1 — in the case of the AX membranes and (1 — in the case of the CX membranes is carried by co-ions and... 

It has previously been shown that large changes can occur in the rate of a cationic polymerization by using a different solvent and/or different counterion (Sec. 5-2f). The monomer reactivity ratios are also affected by changes in the solvent or counterion. The effects are often complex and difficult to predict since changes in solvent or counterion often result in alterations in the relative amounts of the different types of propagating centers (free ion, ion pair, covalent), each of which may be differently affected by solvent. As many systems do not show an effect as do show an effect of solvent or counterion on r values [Kennedy and Marechal, 1983]. The dramatic effect that solvents can have on monomer reactivity ratios is illustrated by the data in Table 6-10 for isobutylene-p-chlorostyrene. The aluminum bromide-initiated copolymerization shows r — 1.01, r2 = 1.02 in n-hexane but... 

Counterion specificity has been observed to be markedly more pronounced for cationic surfactants than for anionic ones. This can certainly be mainly referred to a weaker hydration of typical counter-anions. From the variation of CMC with counterion and from ion activity measurements it can be inferred that the binding to -N(CH3)3 and -NH3 headgroups follows the sequence P>NOj >Br > CP. (As an example a recent study223-1 of decylammonium salts shows the CMC to decrease from 0.064 M for the chloride to 0.038 M for the iodide). The counterion specific effects on micellar shape for -N(CH3)3 surfactants were discussed above. For cationic (as well as some anionic) amphiphiles, a marked counterion specificity is also indicated in the phase diagrams8 but systematic studies of the counterion dependence have not yet been reported. 

Mah et al. demonstrated the effect of counterions on the cationic polymerization of styrene [35-37]. The radiation-induced polymerization is much more sensitive to impurities than the catalytic polymerization, as the former involves the cationic species in a free ion state. Thus, one can expect, in the presence of stable anions, the promotion of the cationic polymerization because of the ion-pair formation between the dimer cation and the counterion. The effect was... 

One must conclude as for the monovalent counterion sequences referred to in the Introduction that interaction between bivalent cations and anions is a complex phenomenon not determined solely by simple electrostatic considerations and ion size. Of the current hypotheses that explain ion sequences, that of Eisenman (45), based on anion field strength and recently expanded to include divalent cation effects (46, 47), seems the most comprehensive. However, we believe a fundamental understanding of these systems awaits better knowledge of the role of such factors as water structure, hydration, and geometric effects, including orientation associated with the presence of an alkyl group and of pH. Studies on a more extensive range of cations are required for all the cited systems, with the possible exception of those based on fatty acids. 

Cationic Surfactants Quaternary ammonium cationic surfactants with alkyl groups of Ci6 to C22 with organic counterions have been smdied extensively [Chou, 1989b] and have been shown to be effective at concentrations as low as 50 ppm [Kawaguchi et al., 2003]. This effectiveness is enhanced by increasing the surfactant concentration and by increasing the counterion/cation ratio, f. 

The role of the counterions is important to the POM self-assembly proeess if hydrophobic interactions and van der Waals forces do not drive the blackberry formation. Past studies have shown that the counterions are effective in the self-assembly process with some contribution from hydrogen bonding. The counterions associated with the large POM macroions are most likely shared between neighboring macroions. In this manner, the like-charged POM macroions, which are expected to repel one another, actually exist close to other POMs. Thus the observation is that there exists an attraction among the like-charged POM macroions. To determine how counterions contribute to blackberry formation, studies were performed to determine the effect of cationic valent state and hydrated size on the blackberry formation, which is described later. 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

Monovalent cations are compatible with CMC and have Httle effect on solution properties when added in moderate amounts. An exception is sUver ion, which precipitates CMC. Divalent cations show borderline behavior and trivalent cations form insoluble salts or gels. The effects vary with the specific cation and counterion, pH, DS, and manner in which the CMC and salt are brought into contact. High DS (0.9—1.2) CMCs are more tolerant of monovalent salts than lower DS types, and CMC in solution tolerates higher quantities of added salt than dry CMC added to a brine solution. 

Lu B, Zheng Y, Scriven LE, Davis HT, Talmon Y, Zakin JL (1998) Effect of variation counterion-to-surfactant ratio on rheology and micro-structures of drag reducing cationic surfactant systems. Rheol Acta 37 528-548... 

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

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