Surfactants anionic evolution

Inherent salt loadings in commercial grade anionic surfactants will influence observed phase evolution processes. 

The partition coefficients for different LAS homologues (Table 5.4.2) are higher in the marine environment due to the higher ionic strength that promotes sorption of anionic surfactants [14] and an increase in the partition coefficient with the alkylic chain length has been observed (Table 5.4.2). The evolution of the concentration of the various homologues of LAS in solids in suspension (cf. Fig. 5.4.2) is similar to that found in water and, in the process of adsorption, an increase can be observed in line with the chain length, as commented on previously. 

The chemistry of olefinsulphonates (AOS) has undergone a strong evolution in the hO" and 70. Perhaps, their production procedures and techniques are most complex among other anionic surfactants consisting of four stages sulphonation, ageing, neutralisation, and hydrolysis [68, 69]. Even Ci2-Cig a-olefms are of major importance as raw material for the olefinsulphonate synthesis. The process scheme is shown in Fig. 1.3. 

The role of surfactants in stabUizing emulsions, as well as the relationship between demulsifier structure and performance, has been identified for over 50 years [J9]. The classification of surfactants as well as demulsifiers is quite arbitrary, but a commonly used one is based on chemical structure [20, 21], Chemical types include nonionic, anionic, and cationic. A brief summary of the evolution in demulsifier chemistry over the years and the effective concentration range is presented in Table 1. The development of chemicals which are more surface active has allowed for reductions in the average dosages. 

YatciUa et al. investigated the conversion of a mixtime of cationic and anionic surfactants to form vesicles. In this case, the reaction was veiy slow and a kinetic phase was associated with the evolution and growth of vesicles over a period of weeks (see Figure 6.12) to a final vesicular system, which, as already mentioned, was thought by the authors to be thermodynamically stable. A subsequent study explored the system CTAB mixed with sodium perfiuorooctanoate. Cylinders, disks, and spherical uni-lamellar vesicles were found to coexist at equilibrium by cryo-TEM. This observation confirms the importance of structural confirmation by cryo-TEM when this technique can be applied. Erom their analysis of the data, the mean curvature modulus, the Gaussian curvature modulus, and the spontaneous curvature could all be evaluated. 

Unzueta and Forcada [93] developed a mechanistic model for the emulsion copolymerization of methyl methacrylate and n-butyl acrylate stabilized by mixed anionic and nonionic surfactants, which was verified by the experimental data. This model is based on the mass and population balances of precursor particles and the moments of particle size distribution. It is sensitive to such parameters as the composition of mixed surfactants and the total surfactant concentration. A competitive particle nucleation mechanism is incorporated into the model to successfully simulate the evolution of particle nuclei during polymerization. 

Recently, W. K. Fischer gave a review of The evolution of surfactant concentrations in German natural waters 1960-1980 [83], following earlier investigations [84] carried out over many years. In addition to the concentration of anionic surfactants obtained by the methylene blue analysis (MBAS), it has also been possible (from 1972) to monitor the values for nonionic surfactants present in natural waters, with the bismuth analysis (BiAS). Fischer found that in the Rhine and in its tributaries, an overall steep decrease of concentrations took place, down to very small residual values (about 0.02-0.1 mg of MBAS/1) as a yearly average, which were only rarely exceeded. He found a significant correlation to the extension of biological treatment plants, which had been carried out in this period. 

---