Type of counterion

The effect is more than just a matter of pH. As shown in Fig. XV-14, phospholipid monolayers can be expanded at low pH values by the presence of phosphotungstate ions [123], which disrupt the stmctival order in the lipid film [124]. Uranyl ions, by contrast, contract the low-pH expanded phase presumably because of a type of counterion condensation [123]. These effects caution against using these ions as stains in electron microscopy. Clearly the nature of the counterion is very important. It is dramatically so with fatty acids that form an insoluble salt with the ion here quite low concentrations (10 M) of divalent ions lead to the formation of the metal salt unless the pH is quite low. Such films are much more condensed than the fatty-acid monolayers themselves [125-127]. 

Unsaturation Value. The reaction temperature, catalyst concentration, and type of counterion of the alkoxide affect the degree of unsaturation. The tendency for rearrangement of PO to aHyl alcohol is greatest with lithium hydroxide and decreases in the following order (100) Li+ >... 

The mechanical properties of ionomers can be appreciably altered by the manner in which the ionomer is prepared and treated prior to testing. Some of the factors that are influential are the degree of conversion (neutralization) from the acid form to the salt form, the nature of the thermal treatment or aging, the type of counterion that is introduced, the solvent that is used for preparation of thin films, and the presence and nature of any plasticizers or additives that may be present. In the scope of this chapter, it is not possible to provide a complete description of the influence of each of these variables on the wide variety of ionomers that are now commercially available or produced in the laboratory. Instead, one or more examples of the changes in properties that may be induced by each of the processing variables is presented and discussed. 

The type of counterion present in an ionomer may, or may not, have a significant effect of properties. For polyethylene-based ionomers, where the presence of crystallinity has an appreciable effect on properties, the type of counterion present does not appear to have a significant effect on either modulus or tensile strength, as Fig. 4 indicates. However, in amorphous ionomers, the effects of changing the counterion from a monovalent one, as in Na or K, to a divalent one, such as Ca, may be appreciable. 

Aside from ion content, a wide range of properties is available in ionomers by control of various processing variables, such as degree of conversion (neutralization), type of counterion, plasticizer content and thermal treatment. Various examples illustrating possible effects of these variables on mechanical relaxation behavior and on such mechanical properties as stiffness, strength, and time- or energy-to-fracture have been given. 

The Krafft point, i.e., the aqueous solubility, also depends greatly on the type of counterion [30,60,61]. For example, potassium salts have higher Krafft points than sodium or ammonium salts. Bivalent cations, like calcium and magnesium, raise the Krafft point. The rise is smaller for ester sulfonates than for alkyl sulfates [61]. 

Because a chemical step is imposed on top of the physical distribution process of partition, there is a great potential for selectivity, as noted by Schill et al, (49>50), Such factors as pH, type and composition of the organic phase, and ionic strength of the aqueous phase can be used to control relative retention. The concentration and type of counterion mainly control the absolute retention. 

Type of counterion Retention increases with the ability of the counterion to form an ion pair. 

It is important to note that the tendency of a monomer towards polymerization and therefore also towards copolymerization is strongly dependent on the nature of the growing chain end. In radical copolymerization the composition of the copolymer obtained from its given monomer feed is independent of the initiating system for a particular monomer pair, but for anionic or cationic initiation this is normally not the case. One sometimes observes quite different compositions of copolymer depending on the nature of the initiator and especially on the type of counterion. A dependence of the behavior of the copolymerization on the used catalyst is often observed with Ziegler-Natta or metallocene catalysts. 

Eq. 8-29 is valid, of course, only up to the solubility product of the salt of the ionized organic species (which is dependent on the type of counterion(s) present). Unfortunately, solubility data of organic salts are scattered and not systematically understood. 

The swelling of plant parenchyma tissue has been ascribed to an electric double layer, which depends significandy on the type of counterions that constitute it monovalent ions cause more swelling than do divalent ions (Shomer et al., 1991), probably because of their larger ionic radius. 

The type of counterion used may affect the retention considerably. The eluotropic strength of the different counterions is usually expressed as an eluotropic series. An example of this is shown in table 3.6. 

Also, the type of counterion may have an effect on selectivity. Especially for anions dramatic differences are sometimes observed (see e.g. ref. [370]). 

M d Type of pairing ion M d Type of modifier M d Type of counterion M c Conc.of counterion M d Type of buffer T c Temperature S d Type of statationary phase In k vs. 1/T linear 3.57... 

While the network density v is more or less given by the concentration of the surfactant, the relaxation time can depend on many parameters such as surfactant concentration, temperature, type of counterions or ionic strength. 

In contrast to RNA, DNA is polymorphic. Under low salt conditions or at high relative humidity, DNA adopts the B-form usually considered to be biologically active. With increasing addition of salt or of polar organic solvents (synonymous with reduced relative humidity or removal of available water of hydration), and with certain types of counterions, DNA and double-stranded synthetic polynucleotides transform from B-DNA to the A-, C-, D-, Z-forms (see Thble 24.1 and Fig. 24.1. Only the A-, B- and Z-DNA structures, which have thus far been determined in detail by single crystal diffraction methods, are of structural interest and they are considered in the following sections. 

Of course, these criteria are only given as an indication of broad tendencies. Factors such as the nature of the catalyst used, the type of counterion and the physical conditions prevailing, are important in determining specific results concerning the course of initiation. 

Establishment of the c.e.c. Involves converting the plates into a state with only one type of counterions (say NH, as in the ammonium acetate method) and then desorbing these quantitatively, measuring how many came off (in the example, by exchange with Na and determining the NH liberated by a Kjeldeihl distillation). Other cationic substances that have been proposed to establish the... 

A great variety of binary Mo-S complex anions is formed and can be isolated in reactions of the tetrathiomolybdate anion [MoS ] " with various suinde and polysulfide anions. The nature of the anionic products that can be isolated from these reactions depends on (a) the amount of excess sulfur used (and the types of ligands present in the reaction mixtures), (b) the type of counterion used in the isolation of the complex anions, and (c) the type of solvent employed in the synthetic procedure. In a recent article, we described a scheme that interrelates the various [Mo2(S),(S2)6-,] anions. In this scheme (Fig. 1), any of the six homologs can hypothetically be obtained from any other by either the addition of sulfur, or the abstraction of sulfur by triphenylphosphine. Experimentally, the correctness of this scheme has been verified by the successful synthesis of most of the [Mo2(S) (S2)6 ] complexes, or of their internal redox isomers. In the [Mo2(S), (82)6 series, the homologs with n = 4, 5, and 6 have been characterized structurally. Those with n = 2 and 3 have been characterized structurally as the internal-redox isomers, [(S4)Mo(S)(//-S)2(S)Mo S2)] (ref. 3) and... 

Additionally, the salt content and the type of counterions in the aqueous phases influence the emulsion stability and consequently SLM degradation. It was found that the amount of liquid membrane removed from SLM increases with a decrease in the salt concentration of the aqueous phases and with an increase in their flow velocities [83]. 

The type of counterion, chloride or methylsulfate, has little influence [36], A more or less extensive ion exchange probably takes place in the rinse liquor with the anionic surfactants coming from the detergent carryover and the anions of water hardness. As a result, it is very likely that no strong difference exists between the two actives once on fabrics [26], This is not in line with other results showing that anionic counterions of the surfactant are present on the fibers, which suggest an ion pair type adsorption [30], For instance, iodide is much more substantive than chloride [98],... 

The type of counterion. Methylsulfate derivatives are somewhat more efficient than chloride ones [1],... 

By far the most important processing variable for mechanical properties is the type of counterion used (Table 3.7). The effects of various counterions incorporated... 

Qian and Qui126 have observed that the morphology of PPy films depends upon the type of counterion used. For example, C104 , BF f, and PF6- yielded films with high concentrations of voids, whereas PPy/pTS films consisted of densely packed nodules. Other workers have noted a dependence of the density of PPy films on the polymerization conditions.115116117 Thus, the change in film morphology may explain the effect of counterion type and polymerization conditions on mechanical properties, as surveyed previously. 

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