Surfactant molecular interactions between,

Photoacoustic FITR (PA-FTIR) is based on measuring the heat associated wifli absrsption of IR lacfiation. The heat generated is released to an inert gas above the sample. The sample can be analysed in the form of a film, and the depth from whidi a signal is obtained can be varied [62]. Evanson et al. [59,60] u PA-FTlR and ATR-PTIR to study die molecular interactions between surfactants and poIy(ethyl acrylate(EA)-methacrylic acid(MAA)) latex and the surface oirichment with nonionic and anioiic surfactants on films formed from die latex. 

There is no molecular interaction between nonionic surfactants with an ethylene-oxide chain, i.e. Genapol and ethoxylated nonylphenols. Indeed, research by Nishikido (6) on polyoxyethylene laurylethers (5 < E.O. number < 49) has shown the ideal behavior (p12 = 0) of their mixtures. Likewise, Xia (7) has found very low p12 values for mixtures of ethoxylated fatty alcohols. 

Fig. 9 Dependence of the molecular interaction between adsorbed dodecyl sulfate ions on the concentration of alkali dodecyl sulfate surfactants...

Our data, to date, show that molecular interaction between two surfactants, both in mixed monolayers at the aqueous solution/air interface and in mixed micelles in aqueous solution, increases in the order POE nonionic-POE-nonionic < POE nonionic-betaine < betaine-cationic < POE nonionic-ionic (cationic, anionic) betaine-anionic cationic-anionic. The greatest probability of synergism exists, therefore, in cationic-anionic mixtures, followed by betaine-anionic mixtures. Synergism can exist in POE nonionic-ionic mixtures only if the surfactants involved have the proper structures. 

The effect of alkyl alcohol on the surface adsorption and micellization of FC surfactant is noticeably different from HC surfactant. The molecular interactions between ROH and C7pNa in the surface layer are shown to be weaker (Smaler l jl-value) as compared with ROH-C, SNa system. 

In the systems with considerable molecular interactions between the two surfactant components, such as CgNBr-CyFNa (cationic-anionic) and CsSOC-CrFNa (nonionic-anionic) systems, the "mutual phobic interaction" can be concealed entirely and there are large negative jSg. and /3m values for these systems. 

Generally, there are two approaches to the investigation of mixed adsorbed films at an oil/water interface. One way is to study mixed adsorption of surfactants from the Scime bulk phase and the other is to study adsorption from both of the bulk phases. The former has been done by many workers from the physicochemical viewpoint to clarify the difference in molecular interaction between the adsorbed state and the bulk state. The latter has been made mostly from the practical point of view, e.g., solvent extraction and complex-forming reactions that take place at the interface, though little is known concerning the thermodynamic viewpoint D). The thermodynamic study is actually useful to elucidate the behavior of film molecules in the adsorbed state. 

Recent molecular dynamics simulations of water between two surfactant (sodium dodecyl sulfate) layers, reported by Faraudo and Bresme,14 revealed oscillatory behaviors for both the polarization and the electric fields near a surface and that the two fields are not proportional to each other. While the nonmonotonic behavior again invalidated the Gruen—Marcelja model for the polarization, the nonproportionality suggested that a more complex dielectric response of water might, be at the origin of the hydration force. The latter conclusion was also supported by recent molecular dynamics simulations of Far audo and Bresme, who reported interactions between surfactant surfaces with a nonmonotonic dependence on distance.15... 

In the real synthesis systems, the surfactant effective packing parameter, g, are mainly affected by the following factors (1) charge, composition, molecular shape, and structure of surfactant, (2) the interactions between surfactant and inorganic species (e.g., charge-density matching), (3) reaction parameters and conditions concentration, pH, ion strength, temperature, etc. 

The order of increased surfactant adsorption on the solid produced by the different alkyl pyrrolidinones parallels the order of their enhancement of superspreading. In addition, it was shown (Wu, 2002) (1) that the change in the spreading coefficient (equation 6.1) parallels enhancement of superspreading and (2) that the order of increased attractive molecular interaction between the different alkylpyr-rolidinones and the trisiloxane surfactant at the hydrophobic solid-aqueous solution interface, as measured by the interaction parameter Psl° (Chapter 11) n-butyl < n-cyclohexyl < -octyl < n-hexyl < 2-ethylhexyl, is exactly the same order as that of their enhancement of the superspreading. 

Figure 16. Schematic of the molecular interactions between HMHEC and surfactant molecules below the critical micelle concentration. Reproduced with permission from ref. 10. Copyright 1987 TAPPI Press.)...

The adsorption kinetics of a surfactant to a freshly formed surface as well as the viscoelastic behaviour of surface layers have strong impact on foam formation, emulsification, detergency, painting, and other practical applications. The key factor that controls the adsorption kinetics is the diffusion transport of surfactant molecules from the bulk to the surface [184] whereas relaxation or repulsive interactions contribute particularly in the case of adsorption of proteins, ionic surfactants and surfactant mixtures [185-188], At liquid/liquid interface the adsorption kinetics is affected by surfactant transfer across the interface if the surfactant, such as dodecyl dimethyl phosphine oxide [189], is comparably soluble in both liquids. In addition, two-dimensional aggregation in an adsorption layer can happen when the molecular interaction between the adsorbed molecules is sufficiently large. This particular behaviour is intrinsic for synergistic mixtures, such as SDS and dodecanol (cf the theoretical treatment of this system in Chapters 2 and 3). The huge variety of models developed to describe the adsorption kinetics of surfactants and their mixtures, of relaxation processes induced by various types of perturbations, and a number of representative experimental examples is the subject of Chapter 4. 

Interactions between surfactants and natural and synthetic polymers have been studied for many years with varying degrees of understanding and experimental control. Although the basic mechanisms of surfactant-polymer interaction are reasonably well known, there still exists substantial disagreement as to the details of some of the interactions at the molecular level. Observations... 

Molecular interactions between two surfactants at an interface or in micelles are frequently described through the so-called parameters, which can be obtained from surface (or interfacial) tension or from critical micellar concentration data [13]. Attractive interactions are characterized by negative values of this parameter and, specifically, it has been found that it becomes less negative as the mole fraction of the co-surfactant increases. It has also been previously observed [14] that this tendency, for different mixed surfactant systems, can be explained by the role played by the interactions of the cationic surfactants head groups in the stability of the mixed micelles. Desai and Dixit [15] have found similar variations depending on the mixtures composition of cationic and polyoxyethylenic non-ionic surfactants. 

We take the bulk solution to be dilute and assume a contact with a reservior, where the surfactant has fixed volume fraction and chemical potential, (pt, and jUb> respectively. Steric and other short-range interactions between surfactant molecules are assumed to take place only within a molecular distance from the interface. This is motivated by the observation that the profile of a soluble surfactant monolayer is in practice almost step-like , the volume fraction at the interface itself being many orders of magnitude larger than that in the solution. 

To the best of our knowledge, report of IL-in-oil (oil-benzene, cyclohexane, n-heptane, etc.) microemulsions using AOT or AOT-derived surfactants was absent in the literature, while water-in-oil RM and microemulsions using AOT or AOT-derived surfactants are well documented in the literature [28,79]. It is proposed that due to the existence of favorable molecular interactions between the inorganic cations of AOT (Na+ NH +, Ca +, etc.) and water molecules, the formation of water-in-oil... 

Some surfactants are used as emulsifiers in processed foods such as bottled salad dressing. An emulsifier causes normally incompatible liquids such as the oil and water in salad dressing to disperse in each other, by forming molecular connections between the liquids. The hydrophobic tails of emulsifier molecules Interact with oil molecules, while the hydrophilic heads on the emulsifier molecules interact with water molecules. 

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