Surfactants electrostatic interaction

Anionic sulfonated polyacrylamide (PAMS) is also found to increase amine flotation of quartz. Although PAMS does not adsorb on the negatively charged quartz and cause no direct activation of amine adsorption, the polymer-surfactant electrostatic interaction can lead to the formation of complexes. This polymer-surfactant complex can reduce the armoring of bubbles and lead to flotation. The anionic polymer can also bridge the adsorbed amine to the amine on the bubble surface and enhance flotation under saturated adsorption conditions. The hydration effect of the polymer may also be responsible for the enhanced flotation in this case. 

Usually, diminishes as the organic solvent concentration increases. For ionic surfactants, solute-surfactant electrostatic interactions are responsible for the shift in sign in at increasing surfactant concentration. These interactions also explain the sign in the trend of the fe-pH dependence, which is sigmoidal and resembles conventional acid-base titration curves. The observed behaviors indicate that the interaction of solutes with the surface of the surfactant-modified stationary phase is stronger than that with micelles. 

Like water-oil-surfactant, IL-oil-surfactant can also form microemulsions. A special feature of IL-based microemulsions is the flexibility of the IL, which can be the polar or nonpolar as well as the surfactant component. When ILs are incorporated into microemulsions with ionic surfactants, electrostatic interactions between the components can play a crucial role to form a more stable palisade layer surrounding the droplets. By using polar ILs, water-free microemulsions can be formed. The tunable properties of two different ILs may allow spontaneous formation of a new class of IL-oil-lL microemulsions with special features opening new fields of application. 

One of the most important characteristics of micelles is their ability to take up all kinds of substances. Binding of these compounds to micelles is generally driven by hydrophobic and electrostatic interactions. The dynamics of solubilisation into micelles are similar to those observed for entrance and exit of individual surfactant molecules. Their uptake into micelles is close to diffusion controlled, whereas the residence time depends on the sttucture of the molecule and the solubilisate, and is usually in the order of 10 to 10" seconds . Hence, these processes are fast on the NMR time scale. 

Emulsifiers (see also Surfactants) 27, 46 End-blockers 12, 18, 19, 76 End-capping 157 End-linking processes 163 End-stoppers (see also End-blockers) 10 End-to-end cyclization 159,160 Energy, cavitation 188,189 —, electrostatic interactions 188, 189... 

Recent development of the use of reversed micelles (aqueous surfactant aggregates in organic solvents) to solubilize significant quantities of nonpolar materials within their polar cores can be exploited in the development of new concepts for the continuous selective concentration and recovery of heavy metal ions from dilute aqueous streams. The ability of reversed micelle solutions to extract proteins and amino acids selectively from aqueous media has been recently demonstrated the results indicate that strong electrostatic interactions are the primary basis for selectivity. The high charge-to-surface ratio of the valuable heavy metal ions suggests that they too should be extractable from dilute aqueous solutions. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

The electrochemical response of analytes at the CNT-modified electrodes is influenced by the surfactants which are used as dispersants. CNT-modified electrodes using cationic surfactant CTAB as a dispersant showed an improved catalytic effect for negatively charged small molecular analytes, such as potassium ferricyanide and ascorbic acid, whereas anionic surfactants such as SDS showed a better catalytic activity for a positively charged analyte such as dopamine. This effect, which is ascribed mainly to the electrostatic interactions, is also observed for the electrochemical response of a negatively charged macromolecule such as DNA on the CNT (surfactant)-modified electrodes (see Fig. 15.12). An oxidation peak current near +1.0 V was observed only at the CNT/CTAB-modified electrode in the DNA solution (curve (ii) in Fig. 15.12a). The differential pulse voltammetry of DNA at the CNT/CTAB-modified electrode also showed a sharp peak current, which is due to the oxidation of the adenine residue in DNA (curve (ii) in Fig. 15.12b). The different effects of surfactants for CNTs to promote the electron transfer of DNA are in agreement with the electrostatic interactions... 

FIGURE 15.13 Schematics of electrostatic interactions between surfactants adsorbed on CNTs and negatively charged DNA molecules. 

These include electrostatic interaction between the particles and interaction of particles with the fluid governed by their wettability, morphology and density (17-19) the extent of adsorption of the polymer and its influence on the interaction of particles, the orientation or configuration of the adsorbed polymers (and surfactant when it is present) and resultant interaction of adsorbed layers the hydrodynamic state of the system and its influence on the interaction of floes themselves. 

Shimomura and Kunitake have reported that stable monolayers and LB films were obtained by electrostatic interaction of water soluble anionic polymers with cationic amphiphiles [58]. This polyion-complexation was also a useful method for stabilization of monolayers of unstable [59] or water soluble anionic surfactants [60]. Mixtures of water soluble cationic and anionic surfactants (1 1) also formed stable Langmuir monolayers at the air/ water interface [60]. 

Ionic surfactants also participate in specific chemical and electrostatic interactions with sorbents that do not occur with non-ionic compounds. In fact, recent research has shown that hydrophobic... 

The slope of unity in region I indicates that the anionic surfactant adsorbs as individual ion through electrostatic interaction with the positively charged surface. 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

Since the stability of CLAs displays a strong dependence on ionic strength, due to electrostatic interactions associated with the surfactant head groups, pH should also have an influence on CLA half-lives. The effect of continuous phase pH on the stability of CLAs dispersed in deionized water at 25°C was investigated by Lye and Stuckey [65]. Above a pH of 6-7, ti/2 values were essentially constant, but began to decline as the continuous phase became more acidic. At low pH values, the excess hydrogen ion concentration led to protonation of the sulfonate head groups of the SDS molecules located at the outer soapy-shell interface. This would have two... 

Modification typically takes advantage of electrostatic interactions between charges on the surface of the macromolecules and the polar headgroups of surfactants. We reasoned that the host-guest interactions at the nanoparticle-solution interface investigated in this work could be used for similar purposes. (From Liu et ah, 2001)... 

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