Surfactants opposite charge

Physical adsorption of surfactants, oppositely charged entities, or polyelectrolytes is another way of modifying of the nanocellulose... 

The Donnan effect acts to exclude like-charged substrate ions from a charged surface region, and this exclusion, as well as the concentration of oppositely charged ions, can be expressed in terms of a Donnan potential pD. Thus for a film of positively charged surfactant ions S one can write... 

For any adsubble method, if the material to be removed (termed the colligend) is not itself surface-active, a suitable surfactant (termed the collector) may be added to unite with it and attach or adsorb it to the bubble surface so that it may be removed (Sebba, Ion Flotation, Elsevier, New York, 1962). The union between colligend and collector may be by chelation or other complex formation. Alternatively, a charged colhgend may be removed through its attraction toward a collector of opposite charge. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

Ejfect of pH It is obvious that in order to recover the protein from reverse micelles, the pH of the stripping solution needs to change toward the pi, which will result in a reduction of the protein interaction with the oppositely charged head groups. The extent of protein recovery from reverse micelles increases with increasing pH for anionic surfactants however, for cationic surfactants the opposite is true. 

The formation of complexes is not restricted to mixtures of polyectrolytes and surfactants of opposite charge. Neutral polymers and ionic surfactants can also form bulk and/or surface complexes. Philip et al. [74] have studied the colloidal forces in presence of neutral polymer/ionic surfactant mixtures in the case where both species can adsorb at the interface of oil droplets dispersed in an aqueous phase. The molecules used in their studies are a neutral PVA-Vac copolymer (vinyl alcohol [88%] and vinyl acetate [12%]), with average molecular weight M = 155000 g/mol, and ionic surfactants such as SDS. The force measurements were performed using MCT. The force profiles were always roughly linear in semilogarithmic scale and were fitted by a simple exponential function ... 

D. J.F. Taylor, R.K. Thomas, and J. Penfold The Adsorption of Oppositely Charged Polyelectrolyte/Surfactant Mixtures Neutron Reflection from Dodecyl Trimethy-lammonium Bromide and Sodium Poly(Styrene Sulfonate) at the AirAVater Interface. Langmuir 18, 4748 (2002). 

C. Monteux, C.E. WiUiams, J. Meunier, O. Anthony, and V. Bergeron Adsorption of Oppositely Charged Polyelectrolyte/Surfactant Complexes at the Air/Water Interface Formation of Interfacial Gels. Langmuir 20, 57 (2004). 

M Hong, BS Weekley, SJ Grieb, JP Foley. Electrokinetic chromatography using thermodynamically stable vesicles and mixed micelles formed from oppositely charged surfactants. Anal. Chem. 70 1394-1403 (1998). 

Khomane et al. prepared dodecanethiol-capped CdS QDs of 4 nm size by using a Winsor II microemulsion system [242], which are soluble in solvents such as n-heptane, toluene, n-hexane, thus demonstrating the dual role of the anionic surfactant, viz., forming the microemulsion and facilitating the extraction of oppositely charged ions from the aqueous to the organic phase. 

CftNBr-CTFNa (cationic-anionic) system. The common cat ionic-anionic mixture of HC surfactants is highly surface active (17), showing the strong interactions between the two oppositely charged surface active ions. Similar re.-sults have been observed in the case of CeNBr-CrFNa system. The "y-log C plot in Fig.5 illustrates such an interaction, lile can see that the 1i1 CeNBr-C-rFNa mixture is much more surface active than CsNBr or CjFNa, The cmc value of surfactants mixture is much more smaller than that of CaNBr or CyFNa, and the-yeme the mixed solution is very low (< 15 rnNrn- ) mixtures with various raolal... 

Surface aggregates formed by ionic surfactant adsorption on oppositely charge surfaces have been shown to be bi layered structures (1.) and are called admicelles<2) in this paper, though they are sometimes referred to as hemimicelles. The concentration at which admicelles first form on the most energetic surface patch is called the Critical Admicellar Concentration (CAC) in analogy to the Critical Micelle Concentration (CMC), where micelles are first formed. Again, in much of the literature, the CAC is referred to as the Hemimicellar Concentration (HMC). 

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