Particles zeta potential

The amount of polymer adsorbed on each sample was measured by pressure filtration through a 0.1 m filter, followed by analysis of the filtrate for residual polymer by gel permeation chromatography with refractive index determination. Particle zeta potentials were measured by taking a small sample of the solids from the centrifuge and re-suspending them in the supernatant prior to analysis in a Malvern Instruments Zetasizer . The concentration of all other types of ions in the supernatant was analysed by ICP atomic emission spectroscopy. 

These stabilizers are added to the formulation in order to stabilize the emulsion formed during particle preparation. These stabilizers, however, can also influence the properties of the particles formed. The type and concentration of the stabilizer selected may affect the particle size. Being present at the boundary layer between the water phase and the organic phase during particle formation, the stabilizer can also be incorporated on the particle surface, modifying particle properties such as particle zeta potential and mucoadhesion (203). Other polymers have also been evaluated as stabilizers in earlier studies such as cellulosic derivatives methylcellu-lose (MC), hydroxyethylcellulose ( ), hydroxypropylcellulose (HPC), and hydroxypropylmethylcellulose (HPMC), as well as gelatin type A and B, carbomer and poloxamer (203). 

Collins and Jameson11 found that for small air bubbles (20 to 100 jzm), varying the particle zeta potential from +30 mV to +60 mV resulted in an order of magnitude change in the observed rate constants for each drop size. Table 9 shows the values of the calculated and observed first-order rate constants for the data of Collins and Jameson obtained when their particles (polystyrene) had the minimum stability (zeta potential + 30 mV). The observed rate constants are much smaller than those calculated from collision theory. Their data indicate that between 1 in 40 to I in 100 collisions results in the particles sticking to bubbles. This is consistent with the particle-collision removal mechanism. 

ZETA POTENTIAL. The potential across the interface of all solids and liquids. Specifically, the potential across the diffuse layer of ions surrounding a charged colloidal particle, which is largely responsible for colloidal stability. Discharge of the zeta potential, accompanied by precipitation of the colloid, occurs by addition of polyvalent ions of sign opposite to that of the colloidal particles. Zeta potentials can be calculated from electrophoretic mobilities, i.e., the rates at which colloidal particles travel between charged electrodes placed in the solution. 

Stern layer—Layer of counterions around the primary charges of a colloid, van der Waal s force—A force of attraction that exists at the surface of a particle as a result of the unbalanced atomic forces at the surface of the particle. Zeta potential—The electric potential at the shear plane. 

Figure 9.4 Calculated particle deposition (5 min in a solution of 10 particles/cm ) for a wafer zeta potential of -10 mV and a particle zeta potential of -19 mV. (From Ref. (3).)...

Another important consideration is solids concentration, since this affects the type of separator to be used. In applications with low solids concentration (e.g., less than 50 ppm), sand filters or cartridge filters may be suitable. If the solids concentration is high, then cake filters are used. Electrical charges on particles affect the agglomeration of particles. Zeta potential measurements may be made but the results are unreliable and have not been used industrially. 

Figure 8. Illustration of the effects of alum treatment on particle Zeta potentials and turbidity levels in water treatment. (Courtesy L. A. Ravina, Zeta-Meter, Inc., Staunton, VA.)...

Soil Clay Pb, Cu, Ca Spiked Evaluation of clay particle zeta potential affecting parameters clay type, pH, ionic strength of pore fluid Vane and Zang (1997)... 

Vane LM, Zang GM. (1997). Effect of aqueous phase properties on clay particle zeta potential and electro-osmotic permeability Implications for electro-kinetic soil remediation processes. Journal of Hazardous Materials 55 1-22. 

As indicated by Eq. 4, the particle velocity measured from the micro-PIV technique is a combination of the electrophoresis velocity of the tracer particles which is related to the particle zeta potential, p, and the electroosmotic flow field which is associated with the zeta potential of the channel surface, If micro-PIV experiments are carried out in an electrolyte in open-end and closed-end microchannels, according to Eq. 4, we can write the expressions for the micro-PlV-measured velocity of the tracer particles in open-end and closed-end rectangular microchannels as below ... 

This expression is fairly accurate for values of down to 0.1. These expressions can be used, provided the validity conditions are met, to find the particle zeta potential and net charge from mobility measurements. Other approximate expressions have been proposed, but we will not go further here (see Makino and Ohshima 2010 and references therein). 

First, if the particles are positively charged or if they are negative but they are less dense than the suspension medium, then the sign of the pressures in the above discussion will be reversed. The initial positive pressure will occur at the anode, rather than the cathode. Thus if the sign of the particle zeta potential is reversed, perhaps by changing the pH, the polarity of the ESA effect will change. This fact makes it easy to accurately determine the isoelectric point from the ESA measurement. 

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