Cationic surfactants acid value

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice. 

The amount of the ester sulfonates, besides the mono- and disalt of the a-sulfo fatty acid, can be calculated by two titrations, one in the acid and one in the basic range. In the basic range both sulfonates and carbocylate functionalities are negatively charged and titrated with the cationic surfactant hyamine. In acid medium the RCOOH group is protonated and no longer available for the titration. Since hyamine-methylene blue (acid conditions) titrates only sulfonate and hyamine-phenol red (basic conditions) determines both sulfonates and carbo-cylates, substraction of the titration value with phenol red from the double value of the titration with methylene blue yields only the a-sulfo fatty acid ester. This is the only species of the three which has merely the sulfonate function [106]. 

It is found in this study that an adjustment of pH value of solution by acid (HF or HC1) to 10.5 is very important for the effective formation of uniform mesopores. However, the acid should be added into the mixture solution after the addition of surfactant otherwise, the formation of the ordered mesoporous structure would be affected. The explanation is that when acid is added to a mixture solution without surfactant, the pH value of system will reduce and subsequently influence the interaction between cationic surfactant and anionic silicate species in the mixture, leading to the poor polymerization of inorganic silicate species. In addition, when HF is used prior to the addition of surfactant, the formation of stable NajSiFg can deactivate the polymerization of silicate species, further terminating the growth of mesoporous framework. 

An anionic surfactant is soluble only at a pH greater than tf pqf its ionizable group, whereas a cationic surfactant (e.g., primary, secondary, ortertiary amines) is soluble only at a pH less than its pKg. However, quaternary ammonium surfactants remain soluble at all pH values. Zwitterionic surfactants, for example, sulfobetaine surfactants, are neutral from pH 2 to 12, whereas some nonionic surfactants, for example, alkyldimethylamine oxides, are converted to cationic surfactants by protonation at acidic pH. 

Under an acidic condition, however, the absolute value of the velocity of the EOF becomes lower than that of the electrophoretic velocity of the SDS micelle and, therefore, the micelle migrates toward the anode. By contrast, when a cationic surfactant is employed instead of SDS, the direction of the EOF wiU be reversed or toward the anode, due to the adsorption of the surfactant molecule on the inside wall of the capillary and changing the surface charges. 

Figure 7.18 shows the adsorption isotherms of aerosol OT (AOT) on alumina and silica from cyclohexane. It can be seen that the anionic surfactant has a greater affinity for the basic oxide than for the acidic oxide. The situation is reversed in the case of the adsorption of the cationic surfactant dimethyl dodecylamine (DDA). DDA adsorbs more on acidic silica than on alumina (Figure 7.19). Calculations based on a plateau adsorption value of about 3x10 mol/m on alumina...

Not surprisingly other cationic surfactants and the alternative surfactant systems listed in Table 1 were also able to generate the three basic structures. The cubic MCM-48 type was most difficult to synthesize and consequently quite rare. Other types of surfactants and/or alternative media (acidic or neutral) allowed preparation and recognition of additional structural kinds of mesoporous materials (which could also be correlated with certain g values). More than 20 types of silica mesoporous materials are listed in a recent compilation as unique in terms of structure and/or method of assembly [18]. Several new cubic structures... 

Numerous other protein-surfactant systems when subjected to Scatchard analysis give curves that extrapolate to a number of specific binding sites very close to the number of cationic amino acid residues in the protein. Furthermore, chemical modification of the cationic sites, e.g., in the case of lysyl residues by acetylation, shifts the Scatchard plots to give lower values of n [32], Despite these interesting observations, Scatchard analysis should be treated with a degree of caution it is not entirely clear why such a good correspondence between n and the number of cationic sites is obtained, since the binding sites must only approximate to independence and are certainly not chemically identical. 

Shapley et al. [125] computed the pX a of benzoic and o-, m-, and p-hydroxy benzoic acids in order to understand the higher ability of the o-hydroxy benzoate to complex to the cationic surfactant headgroups in micelles and adsorbed films. Although the values did not show good agreement with the experimental data, the calculations provided a clear explanation for the unusual behavior of the o-hydroxy benzoate. 

Since alkyl betaines may exist as either zwitte-rionic or cationic surfactants, depending on the pH, their critical micelle concentration shows a complicated behaviour. The CMCs of alkyl betaines are significantly higher in dilute acid solutions than in dilute alkaline solutions because at low pH the surfactant is at least partly in the cationic form (43-45). As the concentration of HCl increases, the amount of the cationic form in solution increases and the resulting CMC of the zwitte-rionic/cationic surfactant mixture increases because the value of the cationic form is higher than that of the... 

Researches have decorated CNT with CHT by surface deposition and crosslinking processes. In this method, the CHT macromolecules as polymer cationic surfactants were adsorbed onto the CNT surface. In this step, a stable dispersion of CNT was formed in an acidic aqueous solution of CHT. The pH value of the system was increased by ammonia solution, and so the CHT could no longer remain in solution. Consequently, the precipitated CHT was deposited on the surface of CNT to form a CHT coating. Finally, the surface-deposited CHT was crosslinked to CNT by glutaraldehyde, for potential applications of this composite in biosensing, gene and drug delivery. 

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