Surfactant concentration effects zeta potential

In this work, the effect of surfactant concentration on the stability of aqueous suspensions was studied by measuring surfactant adsorption and zeta-potential of dispersed particles (1). 

In the context of a study of foam flotation of powdered activated carbon (PAC), Zouboulis et al. [143] noted large and different pH effects when an anionic surfactant was used instead of a cationic one. For the cationic surfactant, best recovery (at low surfactant concentration) was achieved at the highest pH, in agreement with electrostatic arguments (see Section IV.B.l) for the anionic surfactant, an intermediate pH was the best. The authors also measured the zeta potential of the carbon in the presence and absence of the surfactants and concluded that the specific chemical nature and the dissociation of each surfactant. 

Effect of Electrolyte In electrokinetic processes, electrolyte is frequently employed to induce the electrical current to pass through the pore fluid. Electrolyte concentration is associated with electrical potential and power consumption, and affects the zeta potential of soil, thus also influences electroosmotic flow. In general, the presence of an electrolyte reduces the CMC of a surfactant because of a solution-depolarizing effect, so greater micellLzation and less surfactant adsorption can be expected (Saichek and Reddy, 2003a). 

The effect of salt concentration on intermicellar interactions and aggregate structures of anionic and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry, surface tension, zeta potential, cyclic voltammetry measurements and by determining the surfactant NMR self-diffusion coefficients. ... 

Figure 6 shows the effect of surfactant concentration on interfacial tension and electrophoretic mobility of oil droplets (14). It is evident that the minimum in interfacial tension corresponds to a maximum in electrophoretic mobility and hence in zeta potential at the oil/brine interface. Similar to the electrocapillary effect observed in mercury/water systems, we believe that the high surface charge density at the oil/brine interface also contributes to lowering of the interfacial tension. This correlation was also observed for the effect of caustic concentration on the interfacial tension of several crude oils (Figure 7). Here also, the minimum interfacial tension and the maximum electrophoretic mobility occurred in the same range of caustic concentration (17). Similar correlation for the effect of salt concentration on the interfacial tension and electrophoretic mobility of a crude oil was also observed (18). Thus, we believe that surface charge density at the oil/brine interface is an important component of the ultralow interfacial tension.

Villanova et al. reported CNCs-reinforced (ethylacrylate (EA), methyl methacrylate (MMA), and butyl methacrylate (BMA)) mixture matrix-based pharmaceutical acrylic beads via suspension polymerization and direct compression. The results showed narrow size distribution, good flow properties and mechanical stability under compression [223]. Jackson et al. studied the controlled release effect of CNCs modified with cationic surfactant cetyl trimethylammonium bromide (CTAB) on molecules of drug. The results showed increment in zeta potential from -55 to 0 mV in a concentration dependent manner and can bind significant quantities of nanosized molecules of hydrophobic anticancer drug, exhibiting controlled release profile over a 2-day period [224]. 

Although it is not completely clear how surfaces are charged in nonpolar media, two processes seem to dominate [470] surfactant adsorption and proton exchange. If surfactant is present in the solution, it will strongly influence the surface charge of particles due to adsorption to the surface [469]. The effect of surfactant is often not simple. Very different dependencies of the zeta potential on the concentration have been observed [471]. Two examples are plotted in Figure 4.11 (bottom). One shows the zeta potential of titania particles in cyclohexane and the other the surface potential of PMMA particles in hexadecane, both at different concentrations of NaAOT. 

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