Ionic surfactants, effect

Manipulation of electric charge on vesicles by means of ionic surfactants effects of charge on vesicle mobility, integrity, and lipid dynamics. Chem. Eur. J., 3,... 

Walters, K.A. Walker, M. Olejnik, O. Non-ionic surfactant effects on hairless mouse skin permeability characteristics. J. Pharm. Pharmacol. 1988, 40, 525-529. 

Sharma, S.K. Joshi, J.V. Aswal, V.K. Goyal, P.S. Rakshit, A.K. Small-angle neutron scattering of non-ionic surfactant effect of sugars. Pramana-Journal of Physics 2004, 63, 297-302. 

Yaghmur, A., Aserin, A. and Garti, N. (2002) Phase behaviour of microemulsions based on food-grade non-ionic surfactants Effect of polyols and short-chain alcohols. Colloid Surf. A, 209,71-81. 

Joubran, R.F., Cornell, D.G. and Parris, N. (1993) Microemulsions of triglyceride and non-ionic surfactant-effect of temperature and aqueous phase composition. Colloid Surf. A, 80, 153— 157. 

The ernes of ionic surfactants are usually depressed by tire addition of inert salts. Electrostatic repulsion between headgroups is screened by tire added electrolyte. This screening effectively makes tire surfactants more hydrophobic and tliis increased hydrophobicity induces micellization at lower concentrations. A linear free energy relationship expressing such a salt effect is given by ... 

For nonionic amphiphiles, the effects of temperature on the phase behavior are large and the effects of inorganic electrolytes are very small. However, for ionic surfactants temperature effects are usually small, but effects of inorganic electrolytes are large. Most common electrolytes (eg, NaCl)... 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

The study of the mechanism of cloud point micellar extractions by phases of non-ionic surfactant (NS) is an aspect often disregarded in most literature reports and, thus, is of general interest. The effective application of the micellar extraction in the analysis is connected with the principled and the least studied problem about the influence of hydrophobicity, stmcture and substrate charge on the distribution between the water and non-ionic surfactant-rich phase. 

The apparent difference seems to be due to the difference in the binding constants of the complexes to micelles which is much larger in the lipophilic 38c than in the hydrophilic 38b complex27 . A somewhat different, but not an unusual micellar effect is observed in the case of the non-ionic surfactant Triton X-100 as shown in... 

Typical adsorption isotherms are shown in Figs. 16 and 17. Despite the large experimental scatter, a steep increase in adsorption can be seen at low concentrations, followed by a plateau at concentrations exceeding the CMC. Similar behavior has been observed before with model surfactants [49-54] and has also been predicted by modem theories of adsorption [54]. According to Fig. 16, adsorption increases modestly with salinity provided that the calcium ion concentration remains low. The calcium influence, shown in Fig. 17, cannot be explained by ionic strength effects alone but may be due to calcium-kaolinite interactions. 

This paper will be limited to a discussion of our packed column studies in which we have addressed attention to questions regarding, (a) the role of ionic strength and surfactant effects on both HDC and porous packed column behavior, (b) the effects of pore size and pore size distribution on resolution, and (c) the effects of the light scattering characteristics of polystyrene on signal resolution and particle size distribution determination. 

If the gas diffusion between bubbles is reduced, the collapse of the bubbles is delayed by retarding the bubble size changes and the resulting mechanical stresses. Therefore single films can persist longer than the corresponding foams. However, this effect is of minor importance in practical situations. Electric effects, such as double layers, form opposite surfaces of importance only for extremely thin films (less than 10 nm). In particular, they occur with ionic surfactants. 

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

These adverse effects are almost eliminated by using an ionic surfactant to create a very strong sink condition in the acceptor compartment of the permeation cell, and this is the principal focus of our latest research. The charge on the micelles formed from the surfactant also appears to play a role in this respect. 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

The electrostatic and steric effects can be combined to stabilize nanoparticles in solution. This type of stabilization is generally provided by means of ionic surfactants such as alkylammonium cations (Scheme 9.3). These compounds bear both a polar head group which is able to generate an electrical double layer, and a lipophilic side chain which is able to provide steric repulsion [14, 15]. 

Due to their distinctive physico-chemical properties, non-ionic surfactants are applied in the fields of industry, processing technology and science, wherever their interfacial effects of detergency, (de)foaming, (de)emulsification, dispersion or solubilisation can enhance product or process performance. The characteristics of non-ionic surfactants that make them beneficial for detergents include their relatively low ionic sensitivity and their sorptive behaviour [17]. 

This problem was resolved by Nakae et al. [7] using non-polar octadecylsilica as the stationary phase and a solution of 0.1 M of sodium perchlorate in methanol/water (80 20) as the mobile phase. The ternary system (water-alcohol-salt), previously used by Fudano and Konishi [8] as an eluent for the separation of ionic surfactants at higher concentrations, induced the so-called salting out effect . The addition of the organic solvent to the water modified the polarity of the eluent and produced a good separation within a short period of time [9]. It also has the function of dissociating the surfactant micelles in individual molecules that are dissolved in the eluent [8], The presence of the salt (NaC104) in the mobile phase has a considerable influence on... 

Matrix effects can influence significantly the extraction efficiency and signal intensity. For heavily contaminated samples such as sewage sludge, this problem is particularly relevant, and therefore the use of internal standards is essential in these applications. Internal standards applied in the extraction procedures for non-ionic surfactants include perinaphtenone [8], 4-fluoro-4,-hydroxyl-benzophenone [5] and 4-bro-mophenyl acetic acid [9]. More appropriate are internal standards from the same compound class butylphenol [10], heptylphenol [11],... 

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