Surfactants in aqueous

Ahphatic amine oxides behave as typical surfactants in aqueous solutions. Below the critical micelle concentration (CMC), dimethyl dodecyl amine oxide exists as single molecules. Above this concentration micellar (spherical) aggregates predorninate in solution. Ahphatic amine oxides are similar to other typical nonionic surfactants in that their CMC decreases with increasing temperature. 

R. Zana, C. Weill. Effect of temperature on the aggregation behavior of nonionic surfactants in aqueous solutions. J Physique Lett 46 L953-L960, 1985. 

The IFT value also increases with increasing di monosulfonate ratio for a smaller series of AOS 1618 surfactants (entries 8-11, Table 13). This can be seen more clearly in Fig. 10. The same trend is also observed for AOS 2024 surfactants in aqueous 4% NaCl (entries 14-17, Table 13). However, this trend is not observed for AOS 1416 (entries 12 and 13, Table 13). 

The change in surface wettability (measured by the contact angle) with concentration for the three surfactants is plotted in Fig. 2.54 (Zhang and Manglik 2005). The contact angle reaches a lower plateau around the CMC where bilayers start to form on the surface. Wettability of non-ionic surfactants in aqueous solutions shows that the contact angle data attains a constant value much below CMC. Direct interactions of their polar chain are generally weak in non-ionics, and it is possible for them to build and rebuild adsorption layers below CMC. The reduced contact an-... 

A protocol should be designed to conform as closely as possible to all ERA requirements. The test substance is a typical end-use product and application and agronomic practices accurately reflect the label and normal crop culture in the areas where the study will be conducted. Dislodging leaf material with a surfactant in aqueous... 

When the variation of any colligative property of a surfactant in aqueous solution is examined, two types of behavior are apparent. At low concentrations, properties approximate those to be expected from ideal behavior. However, at a concentration value that is characteristic for a given surfactant system (critical micelle concentration, CMC), an abrupt deviation from such behavior is observed. At concentrations above the CMC, molecular aggregates called micelles are formed. By increasing the concentration of the surfactant, depending on the chemical and physical nature of the molecule, structural changes to a more... 

The trend of discovering the analytical field of environmental analysis of surfactants by LC-MS is described in detail in Chapters 2.6-2.13 and also reflected by the method collection in Chapter 3.1 (Table 3.1.1), which gives an overview on analytical determinations of surfactants in aqueous matrices. Most methods have focused on high volume surfactants and their metabolites, such as the alkylphenol ethoxylates (APEO, Chapter 2.6), linear alkylbenzene sulfonates (LAS, Chapter 2.10) and alcohol ethoxylates (AE, Chapter 2.9). Surfactants with lower consumption rates such as the cationics (Chapter 2.12) and esterquats (Chapter 2.13) or the fluorinated surfactants perfluoro alkane sulfonates (PFAS) and perfluoro alkane carboxylates (PFAC) used in fire fighting foams (Chapter 2.11) are also covered in this book, but have received less attention. 

Modern methods of sample handling for determination of surfactants in aqueous samples are practically all based on SPE and modifications thereof. Substantial reductions in analysis time, solvent consumption, sample volume required, and number of off-line steps have thus been achieved. This has not only increased the analysts capacity and analysis price per sample, but also decreased the risk of both analyte loss and contamination during sample handling. Whether or not this has indeed resulted in an increased quality of analytical results still needs to be validated through, e.g. intercalibration exercises. This aspect is discussed in more detail in Chapter 4. 

Levine, L.H. Garland, J.L. Johnson, J.V. HPLC/ESI-Quadrupole Ion Trap-MS for Characterization and Direct Quantification of Amphoteric and Nonionic Surfactants in Aqueous Samples. Anal. Chem. 2002, 74, 2064-2071. 

M. Ahngren, P. Hansson, E. Mukhtar, and S. van Stam Aggregation of Alkyltrimethylammonium Surfactants in Aqueous Poly(Styrenesulfonate) Solutions. Langmuir 8, 2405 (1992). 

Zhang et al. [135] have studied the physicochemical behavior of mixtures of -dodecyl-/l-D-maltoside with anionic, cationic and nonionic surfactants in aqueous solutions. To acquire information on the property of mixed micelles, the characteristic change of pyrene with changes in polarity was monitored. The polarity parameter at low concentrations was found to be 0.5-0.6. 

Introduction to the variety of types of surfactants, effect of surfactants on aqueous solution properties. Law of mass action applied to the self-assembly of surfactant molecules in water. Spontaneous self-assembly of surfactants in aqueous media. Formation of micelles, vesicles and lamellar structures. Critical packing parameter. Detergency. Laboratory project on determining the charge of a micelle. 

Non-ideal solution theory is used to calculate the value of a parameter, S, that measures the interaction between two surfactants in mixed monolayer or mixed micelle formation. The value of this parameter, together with the values of relevant properties of the individual, pure surfactants, determines whether synergism will exist in a mixture of two surfactants in aqueous solution. 

Table 6.1 Theoretical estimation of the types of structures of protein self-assembly induced by interactions of food proteins (0.5 % w/v) with food-grade surfactants in aqueous solution (pH = 7.2, ionic strength = 0.05 M, 293 K) below the cmc (CITREM cmc = 15 mg/L SSL cmc = 3.5 mg/L PGE cmc = 1.0 mg/L (IFin el al., 2005)). See the text for definitions of k and k2.

Kelley, D., McClements, D.J. (2003). Interactions of bovine serum albumin with ionic surfactants in aqueous solutions. Food Hydrocolloids, 17, 73-85. 

Alexandridis P, Hatton TA. Polyethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) block copolymer surfactants in aqueous solutions and at interfaces thermodynamics, structure, dynamics, and modeling (review). Colloid Surf A Physicochem Eng Aspects 1995 96 1 16. 

This explanation for the entropy-dominated association of surfactant molecules is called the hydrophobic effect or, less precisely, hydrophobic bonding. Note that relatively little is said of any direct affinity between the associating species. It is more accurate to say that they are expelled from the water and —as far as the water is concerned —the effect is primarily entropic. The same hydrophobic effect is responsible for the adsorption behavior of amphi-pathic molecules and plays an important role in stabilizing a variety of other structures formed by surfactants in aqueous solutions. 

Bahadur, P, N. V. Sastry, andY. K. Rao. 1988. Interaction studies of styrene-ethylene oxide block copolymers with ionic surfactants in aqueous solutitSholloids Surf.29 343-358. 

Lawrence, M.J., S.M. Lawrence, and D.J. Barlow. 1997. Aggregation and surface properties of synthetic double-chain-ionic surfactants in aqueous solution. J Pharm Pharmacol 49 594. 

Figure 11.5 Self-assembly of surfactants in aqueous phase.

N. Nishikido and R. Matuura, The effect of added inorganic salts on the micelle formation of nonionic surfactants in aqueous solutions, Bull. Chem. Soc. Japan 50 (1977) 1690-1694. 

Carale, T.R., Q.T. Phan, and D. Blankschtein. 1994. Salt effects on intramicellar interactions and micellization of nonionic surfactants in aqueous solutions. Langmuir, 10, 109-121. 

The determination of anionic surfactants in aqueous samples involves the following analytical steps ... 

Small shifts of the same bands are observed for nanotubes solutions with Tween but these shifts are smaller (by about 5-7 meV). The greatest shift of bands (up to 70 meV) can be seen for absorption spectra of nanotubes with SDS. So, the interaction between SWNT and surfactant in aqueous solution leads to the increase of the semiconducting nanotubes band gap, especially for a surfactant with a charge group. 

SWNT interactions with different surfactants in aqueous solution result in changes in Raman spectra, as compared with spectra of a nanotube in films (Fig. 4). In this Figure two spectral intervals with bands corresponding to RBM and G mode are shown. Each Raman spectrum is normalized to the most intense band corresponding to the G-mode. The interaction with different surfactants leads to the intensity decrease and shift of lines attributed to the RBM. The essential changes in spectra are observed for this mode of SWNT in aqueous solutions with SDS. The intensity of the low-... 

The following surfactants have been tested (A) Potassium benzenesulfonate in heptane (Kertes and Gutman, 1976), (B) Tri- -dodecylammonium bromide in cyclohexane (Reemik, 1965), (3) Tri-n-dodecylammonium bromide in benzene (Reemik, 1965), (D) Tri-n-dodecylammonium tetrachloroferrate in benzene (Kertes et al., 1970), (E) Most surfactants in aqueous solutions (Ward and du Reau, 1993)... 

Silicone surfactants in aqueous solutions show the same general behavior as conventional hydrocarbon surfactants - the surface tension decreases with increasing concentration until a densely packed film is formed at the surface. Above this concentration, the surface tension becomes constant. The concentration at the transition is called the critical micelle concentration (CMC) or critical aggregation concentration (CAC). The surface and interfacial activity of silicone surfactants was reviewed by Hoffmann and Ulbricht [27]. Useful discussions of the dependence of the surface activity of polymeric silicone surfactants on molecular weight and structure are given by Vick [28] and for the trisiloxane surfactants by Gentle and Snow [29]. 

---