Ethoxylated surfactant, discussion

Anionic alkyl ether sulfate surfactants are produced by sulfating nonionic alcohol polyalkyloxylates such as the ethoxylated surfactants discussed earlier. The sul-fated products generally contain variable amounts of unconverted alcohols and inorganic salts as reaction by-products. Determination of the ratio of anionic to nonionic components in surfactant mixtures is desired for quality control and performance evaluation. Separation of the ionic sulfate and nonionic alcohol components is achieved by reversed-phase chromatography. The separation of four alkyl ether sulfate surfactants is shown in Table 3. 

Ethoxylated surfactants were chosen for study based on predicted foaming properties, thermal and chemical stability, and adsorption characteristics. Only foaming properties are discussed herein. 

As discussed in Chapter 10, microemulsions, which may be considered as swollen micelles, are more effective in solubilization of many agrochemicals. Oil-in-water microemulsions contain a larger hydrocarbon core than surfactant micelles and hence they have a larger capacity for solubilizing lipophilic molecules such as agrochemicals. However, with polar compounds, O/W microemulsions may not be as effective as micelles of ethoxylated surfactants in solubilizing the chemical. Thus, one has to be careful in applying microemulsions without knowl-... 

If the nonionic surfactant is extracted from water into an organic solvent as its potassium tetrathiocyanatozincate(II) complex, its original concentration can be related to the concentration of zinc in the extract, as determined by atomic absorption spectrometry (117) or visible spectrophotometry (118). The gravimetric barium chloride/molybdophosphoric acid method for determination of nonionics has also been adapted to an atomic absorption finish, with the residual molybdenum being determined in the supernate after centrifugation (45). Similarly, the bismuth in the barium/ethoxylated surfactant/tetraiodobismuthate precipitate can be determined by AAS (52). This procedure is discussed with gravimetric analysis. 

A review of the preparation, properties, the uses of surface-active anionic phosphate esters prepared by the reactions of alcohols or ethoxylates with tetra-phosphoric acid or P4O10 is given in Ref. 3. The preparation and industrial applications of phosphate esters as anionic surfactants were also discussed in Ref. 31. 

Gas chromatography (GC) has developed into the most powerful and versatile analytical separation method for organic compounds nowadays. A large number of applications for the analysis of surfactants have emerged since the early 1960s when the first GC papers on separation of non-ionics were published. The only major drawback for application of GC to surfactants is their lack of volatility. This can be easily overcome by chemical modification (derivatisation), examples of which will be discussed extensively in the following paragraphs. This chapter focuses on surfactant types, and in addition discusses some structural aspects of alkylphenol ethoxylates (APEOs) that are important for, as well as illustrative of, aspects of separation and identification that are linked to the complexity of the mixtures of surfactants that are involved. 

In this chapter, all four types of sediment and sludge sample handling techniques for non-ionic surfactants will be discussed and compared. Most of the studies published on non-ionics focus on APEOs and their degradation products, viz. the alkylphenols, but some extraction methods for alcohol ethoxylates (AEOs) and coconut diethanol amides will also be discussed. 

This paper will review the biodegradation of nonionic surfactants. The major focus will be on alcohol ethoxylates and alkylphenol ethoxylates—the two largest volume nonionics. In this paper the effect of hydrophobe structure will be discussed, since hydrophobe structure is considered more critical than that of the hydrophile in biodegradability of the largest volume nonionics. The influence of the hydrophobe on the biodegradation pathway will be examined with an emphasis on the use of radiolabeled nonionics. 

As discussed previously, the biodegradation pathways using non-selected bacterial inocula for nonionic ethoxylates may be divided into two distinct areas, each dependent on the structure of the surfactant. 

Ethoxylated nonionic surfactants approximately obey a hnear mixing rule expressed as Eq. 1 when the characteristic property is the averaged number of ethylene oxide groups per molecules (EON) [35]. The goodness of the fit depends on the partitioning phenomena, which will be discussed later, in Sect. 4. 

It was observed that the formulations consisting of ethoxylated sulfonates and petroleum sulfonates are relatively insensitive to divalent cations. The results show that a minimum in coalescence rate, interfacial tension, surfactant loss, apparent viscosity and a maximum in oil recovery are observed at the optimal salinity of the system. The flattening rate of an oil drop in a surfactant formulation increases strikingly in the presence of alcohol. It appears that the addition of alcohol promotes the mass transfer of surfactant from the aqueous phase to the interface. The addition of alcohol also promotes the coalescence of oil drops, presumably due to a decrease in the interfacial viscosity. Some novel concepts such as surfactant-polymer incompatibility, injection of an oil bank and demulsification to promote oil recovery have been discussed for surfactant flooding processes. 

Figure 1. Structural formulas of the ethoxylated alcohol and phospholipid surfactants used in the affinity precipitation of avidin. Octaethyleneglycol mono-n-dodecylether (C12E8) was used as a solubilizing surfactant and dimyristoylphosphatidylethanolamine (DMPE) was used as the insoluble surfactant to which biotin was covalently attached. (The structural formula of the derivatized phospholipid and a discussion of the reaction and purification scheme have been previously described by Powers et (7)).

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

Both anionic and nonionic surfactants are used in the formulation of liquid detergents. Surfactants are primarily responsible for wetting the surfaces of fabrics as well as the soil (reducing surface and interfacial tension), helping to lift the stains off the fabric surface, and stabilizing dirt particles and/or emulsifying grease droplets [1-4], The main anionic surfactants are sodium alkylbenzene sulfonates, alkyl sulfates, and alkylethoxylated sulfates. The nonionic surfactants used to formulate heavy-duty liquids are primarily ethoxylated fatty alcohols. Other surfactants are also used in HDLDs and are discussed in a subsequent section. 

The rate constants for a variety of micro emulsions based on a non-ionic surfactant and formulated with or without an alcohol as co-surfactant were determined from the slopes of the straight line obtained by plotting the reverse concentration of substrate against reaction time. The results are compiled in Table 5.1. It can be seen from the table that rather similar values were obtained for all the microemulsions based on an alcohol ethoxylate as surfactant. The reaction was more sluggish in the microemulsion based on the sugar surfactant octyl glucoside (CgGi). A probable reason for this difference was discussed... 

---