Zeta potential scale

Zeta potential helps to determine stabiUty of dispersion. The following are the turning points on zeta potential scale ... 

The velocity of particle migration, v, across the field is a function of the surface charge or zeta potential and is observed visually by means of an ultramicroscope equipped with a calibrated eyepiece and a scale. The movement is measured by timing the individual particles over a certain distance, and the results of approximately 10-15 timing measurements are then averaged. From the measured particle velocity, the electrophoretic mobility (defined as v/E, where E is the potential gradient) can be calculated. 

Consider a simple interfacial region at a mercury/solution interface. The electrolyte is 0.01 M NaF and the charge on the electrode is 10 iC negative to the pzc. The zeta potential is -10 mV on the same scale. What is the capacitance of the Helmholtz layer and that of the diffuse layer Galculate the capacitance of the interfaces. Take the thickness of the double layer as the distance between the center of the mercury atoms and that of hydrated K+in contact with the electrode through its water layer. (Bockris)... 

In addition to the Peclet number, one can also define other dimensionless groups that compare either relevant time scales or energies of interaction. Using some of the concepts previewed in Section 4.7c and Table 4.4, one can define an electrostatic group (in terms of the zeta potential f and relative permittivity cr of the liquid) as... 

Concentration profiles were derived by gray-scale analysis from the images mentioned above [92], Whereas without use of zeta potential variation no difference in concentration profiles between the upstream and downstream positions is visible, a much more flattened, i.e. mixed, profile results under electrokinetically driven conditions in the downstream position. 

FIGURE 31.9 Correlation of surfactant micellar zeta potential and micelle charge density with zein dissolution showing that protein denaturation potential scales linearly with the micellar charge/potential. 

The second equality is obtained by using Eq. (7-lla) for Wmin- Equation (7-33) predicts that Ob should scale with particle volume fraction as zeta potential as cTg ft cTg o — where crg,o is the Bingham yield stress at zero zeta potential, and is a constant. These scalings have been observed in several experiments (Firth 1976). 

The thermal energy of a particle scales as kT, while with a — the van der Waals attractive energy scales as the Hamaker constant A (Eq. 8.1.20). Finally from Eq. (8.1.15), the energy of repulsion is seen to scale as ae for small zeta potentials, say f less than the Nernst potential at standard temperature (26 mV), and for small Debye length to radius ratio. 

The parameter n refers to the ratio of the zeta potential in the sample and the BGE regions. Typical values of this parameter range between 0.2 and 0.3 [50,51], so that the advective dispersion effects of mismatched slip velocities is negligible for low y but dominates at high y. An analogous scaling... 

Microfluidic and nanofluidic chips have a wide range of applications in the chemical, biomedical, environmental, and biology areas, where a variety of chemical solutions are used. With the development of microfabrication technology, many new materials such as PDMS and poly (methyl methacrylate) (PMMA) are also employed for chip fabrication. Since each pair of sohd-liquid interface has its unique zeta potential and electroosmotic mobility, which have significant influences on flow control in such small-scale devices, it is very important to experimentally determine these two parameters using the current monitoring technique in order to develop microfluidic and nanofluidic devices for various applications. 

Thin EDLs form at both the particle and the wall surfaces. The formation of EDLs at the surfaces sets the fluid in motion and consequently drives the particle. As the particle is located at the center of the microchaimel, it experiences neither vertical translation nor rotation. Figure 7 shows the instantaneous location of the particles with different zeta potentials. The translational velocity U of the particle is given by the gradient of the graph. For all cases, the gradient is cimstant. This implies that the particles accelerate in a very short time to a constant velocity and move with that constant velocity thereafter. This is not unexpected as the inertia force is negligible in such a small-scaled channel. 

In order attain measurable SHG signals, pulsed femtosecond lasers with large intensities are usually employed (Yan et al. 1998 Schneider et al. 2007). It was possible to show that the SHG scales with surface potential and the independently measured zeta-potentials can be reproduced by adopting appropriate models for the electric double layer (Yan et al. 1998). More generally, SHG is directly related to the surface excess of adsorbate as shown for malachite green on polystyrene (Eckenrode et al. 2005). This technique offers the opportunily for online and in situ characterisation of colloidal suspensions with particle sizes considerably larger than 5 nm (Schneider and Peukert 2007 Schiirer and Peukeit 2010). 

Tournassat et al. (2009) compared the BSM and TLM models with molecular dynamics simulations of a montmorillonite/water interface at the pore scale in 0.1 M NaCl. Simulation-derived values were compared with macroscopic model results obtained from the classical models. Although the Na concentration profile is well reproduced in the diffuse layer, anion exclusion is overestimated by the BSM and TLM theories under the experimental conditions employed the agreement between molecular dynamics simulated and modeled diffuse-layer composition is less accurate with TLM than with BSM. However, the potentials at the three planes of interest are accurately reproduced. It was also showed that molecular dynamics simulations can be used to constrain BSM parameters or, in combination with zeta potential measurements, TLM parameters, by providing suitable values for the capacitance parameters. 

Tsai et al. (2007) investigated flotation for CMP wastewater treatment at both the lab and pilot scale. The CMP wastewater had a pH of 9.4, total solids of 8200 mg/L, total Si of 4(X)0 mg/L, turbidity of550 NTU, zeta potential of —50 mV, and a mean particle size of 106 nm. Following screening of alternative coagulants and surfactants, they used a 2k factorial design to evaluate removal efficiency for total solids, dissolved silica, and mrbidity as a function of four operating variables PACl concentration, sodium oleate concentration, hydraulic residence time, and recycle ratio. Optimal... 

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