Hydrophobic structure surfactants

As mentioned before, the presence of surfactants in anaerobic compartments cannot be separated from their physico-chemical characteristics and in fact surfactants which degrade extensively in the laboratory under anaerobic conditions, e.g. soap, are also found in considerable concentrations in anaerobic compartments. Due to their hydrophobic character surfactants are strongly sorbed to sludges and therefore a large amount of the load of these compounds into a sewage treatment plant (reportedly 20-50%) is associated with suspended solids [43,44]. The relevance of the presence of surfactants in the environment should be assessed, therefore, on the basis of their potential impact on the structure and function of the various compartments. In most cases, ionic surfactants are present as insoluble salts and therefore their potential impact is negligible as reflected in the lack of known negative impacts. 

The soil properties observed with these chemicals suggest that the chemical structural requirements for an hydrophobic cationic surfactant appear to be ... 

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. 

The specific probes that we have used in our investigations have included TS itself and a variety of hydrophobic and surfactant trans-stilbenes having the structures shown below (SNA, MSNA and MSM). 

Most non-polymeric antistatic finishes are also surfactants that can orient themselves in specific ways at fibre surfaces. The hydrophobic structure parts of the molecule act as lubricants to reduce charge buildup. This is particularly true with cationic antistatic surfactants that align with the hydrophobic group away from the fibre surface, similar to cationic softeners (see Chapter 3, Fig. 3.1). The main antistatic effect from anionic and non-ionic surfactants is increased conductivity from mobile ions and the hydration layer that surrounds the hydrophilic portion of the molecule since the surface orientation for these materials places the hydrated layer at the air interface. 

To obtain a wide w/o microemulsion phase it is essential to adjust carefully the cosurfactant structure (usually its chain length) and its relative amount. Although trial and error is still the most commonly used method for obtaining microemulsions, a tentative rule is to combine a very hydrophobic cosurfactant (n-decanol) with a very hydrophilic ionic surfactant (alcohol sulfate) and a less hydrophobic cosurfactant (hexanol) with a less hydrophilic ionic surfactant (OTAB). For very hydrophobic ionic surfactants, such as dialkyl dimethylammonium chloride, a water-soluble cosurfactant, such as butanol or isopropanol, is adequate (this rule derives at least partially from the fact that an important feature of the cosurfactant consists of readjusting the surfactant packing at the solvent/oil interface). 

Up to this point, only symmetrical ions have been considered, although structural eflFects can also be identified in the case of unsym-metrical ions. For instance, all the atoms in the NO3" ion are planar and consequently this ion can be a structure-breaker in the planar direction but an electrostrictive structure-maker at 90° to the plane. Thus, this ion could be said to be polyfunctional. As it turns out, the NO"3 ion is a net structure-breaker as shown in Figure 6. The cationic CH3-(CH2)h-N -(CH3)3 and anionic CH3-(CH2) -S04 surfactants can also be polyfunctional, but as n becomes large, they should be net hydrophobic structure-makers (8). Another class of polyfunctional ionic species are the dipolar ions such as the amino acids,... 

It will be noted that HLB numbers are most often used in connection with nonionic surfactants. While ionic surfactants have been included in the HLB system, the more complex nature of the solution properties of the ionic materials makes them less suitable for the normal approaches to HLB classification. In cases where an electrical charge is desirable for reasons of stabihty, it is often found that surfactants that have limited water solubiUty and whose hydrophobic structure is such as to inhibit efficient packing into micellar structures should be most effective emulsifiers. Surfactants such as the sodium trialkylnaphthalene sulfonates and dialkylsulfo-succinates, which do not readily form large micelles in aqueous solution, have found some use in that context, usually providing advantages in droplet size and stabihty over simpler materials such as sodium dodecyl sulfate. 

Associative thickeners are low-molecular-mass water-soluble polymers with at least two hydrophobes such as hydrophobically modified ethylene oxide-urethane block copolymers (HEUR) or hydrophobically modified hydroxyethylcellulose (HMHEC). The hydrophobes can associate with themselves or with hydrophobes on surfactant, cosolvent, latex, and pigment. This sets up a loose network that is sensitive to mechanical disturbance but re-forms quickly. The result is that pigment settling and film sag are reduced because the network structure increases the low shear viscosity, but the formulations show easy... 

Surfactant Structure. Surfactants in this section are defined as amphipolar or amphipathic molecules composed of a hydrophilic head and a hydrophobic tail group. A detailed description of surfactants and surfactant structure can be found in Chapter 1. Surfactants are generally classified according to their hydrophilic head group. Common classifications are ... 

Kinetic measurement data provide information about diffusional transport via macropores, mesopores, and micropores, and thus characterize pore structure. Increasing the period of presoaking resulted in increased swelling and permeability, which led to the increased speed of leach-out (i.e. macrodiffusion, characterized by ki and kj), in similarity with break-in. The effects of hydrophobization with surfactants are also relevant rate constants are higher than those for no soaking and no hydrophobization. 

It must be noticed that resolution of compounds with different and high hydrophobicity using SDS as surfactant in MEEKC sometimes may be unsuccessful [44], Double-chain structure surfactants such as phosphatydUchoUne achieved a better selectivity compared to the traditional MEEKC-SDS system [7,22]. 

Surfactants Surfactants are compounds that have both hydrophihc and hydrophobic structures. They can form micelles with fat, oil, and proteins in water and help to clean the membranes fouled by these materials. Some surfactants may also interfere with hydro-phobic interactions between bacteria and membranes. In addition, surfactants can dismpt functions of bacteria cell walls. They therefore affect fouling dominated by the formation of biofilms (Pall, 2006). 

Fig. 4.38 Water-heptane interfacial tension as a function of surfactant concentration. Effect of hydrophobe structure. (From Ref. 101. Reproduced by permission of Academic Press.)...

The cmc of a fluorinated surfactant also depends on the nature of the hydrophile but to a lesser effect than on the hydrophobe structure (Table 6.9). The carboxy-lates have higher cmc values than sulfonates (Table 6.11). This is in accord with the order of decreasing cmc values—carboxylates > sulfonates > sulfates—observed by Klevens [145] for hydrocarbon-type surfactants. 

Surfactants are long-chain compounds containing a hydrophobic tail and an ionic head. In polar solvents the surfactants arrange themselves in a spherical structure known as a micelle in which the hydrophobic tails form the... 

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

FIG. 1 Self-assembled structures in amphiphilic systems micellar structures (a) and (b) exist in aqueous solution as well as in ternary oil/water/amphiphile mixtures. In the latter case, they are swollen by the oil on the hydrophobic (tail) side. Monolayers (c) separate water from oil domains in ternary systems. Lipids in water tend to form bilayers (d) rather than micelles, since their hydrophobic block (two chains) is so compact and bulky, compared to the head group, that they cannot easily pack into a sphere [4]. At small concentrations, bilayers often close up to form vesicles (e). Some surfactants also form cyhndrical (wormlike) micelles (not shown). 

Amphiphilic molecules (surfactants) are composed of two different parts hydrophobic tail and hydrophilic head [1 ]. Due to their chemical structure they self-assemble into internal surfaces in water solutions or in mixtures of oil and water, where the tails are separated from the water solvent. These surfaces can form closed spherical or cylindrical micelles or bicontinuous phases [3,5]. In the latter case a single surface extends over the volume of the system and divides it into separated and mutually interwoven subvolumes. 

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