The stability of particles in solution can be quantified by measuring the Zeta potential of the particles. Zeta potential is the measurement of the electric potential at the slipping plane in the double layer surrounding a particle in liquid suspension. While not measured directly, Zeta potential can be calculated using theoretical models and measuring the electrophoretic mobility of the particles. An induced electric field causes charged particles in solution to move toward the electrode opposite their surface charge. The velocity of the charged particles moving toward the electrode is proportional to the amount of charge of the particle. Using Electrophoretic light scattering, the velocity of the particles can be determined by measuring the frequency shift of the light scattered by the particles in motion.

Typical Experimental Results:

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Zeta potential analysis of particles in solution

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Zeta potential distribution graph of nanoparticles in solution

 

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Zeta potential as a function of pH level

Applications:

Effect of Additives Electroosmotic Flow Electrophoretic Light Scattering
Isoelectric Point Oil Suspensions Organic Mixtures
Particle Agglomeration/Coagulation Particle Mobility Particle Suspensions
pH Analysis pH Titration Polishing Slurries
Sedimentation Surface Charge Suspension Stability and Shelf Life

 

For more information please read our application notes:
Zeta Potential of Silica Slurry as a Function of pH

 

Instruments: Delsa Nano C Nano Particle Size and Zeta Potential Analyzer

particle size

Key Specifications:

Concentration Range 0.001%-40%
Max Heating Temp 90 degrees C
Max Cooling Temp 15 degrees C below ambient temp
pH Range 1-13
Zeta Potential Range -100 – +100mV
Scattering Angle 15, 30, 160 degrees
Flow Cell Sample Requirements 0.7mL
High Concentration Cell Sample Requirements 1mL

 

Zeta Potential of Silica Slurry as a Function of pH

 

In colloidal systems, Zeta potential is the electric potential at the slipping plane in the double layer surrounding a particle suspended in a fluid, in reference to a point in the bulk fluid far away from the particle. In other words, zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle. The double layer is composed of the stationary Stern layer and the diffuse layer. The Zeta potential, measured in mV at the slipping plane or the interface between the Stern layer and the diffuse layer is widely used as a measure of the particle stability in colloids. The higher the Zeta potentials absolute values are the more stable the particles in the colloids.

 

Zeta potential is not measurable directly but it can be calculated using theoretical models and an experimentally-determined electrophoretic mobility. When an electric field is applied to charged particles in the colloids, particles move toward an electrode opposite to their surface charge. Since the velocity is proportional to the amount of charge of the particles, zeta potential can be estimated by measuring the velocity of the particles. Electrophoretic light scattering is the method most popularly used to determine the velocity of the particles suspended in a liquid medium under an applied electric field. In order to determine the speed of the particles, the particles are irradiated with a laser light and the scattered light emitted from the particles is detected. Since the frequency of the scattered light is shifted from the incident light in proportion to the speed of the particles movement, the electrophoretic mobility of the particles can be measured from the frequency shift of the scattered light.

 

AppNote-33

 

For polishing slurry, stability is very important. If the Zeta potential is too low, particles will agglomerate and create large clusters. These large clusters can lead to undesired deep scratches in the polishing surface. For applications that require very smooth surfaces, these scratches can be devastating.

 

By using the DelsaNano C Particle and Zeta Potential Analyzer, Auto Titrator and the Flow Cell, the Zeta Potentials of a colloidal silica polishing slurry were measured as a function of solution pH values. Figure 1 shows the experimental results on the Zeta potentials of this colloidal silica polishing slurry from 3 to 12pH. It is found that a pH level between 10 and 11pH will result in the highest absolute Zeta potential values. The results indicate that the Zeta potential may be controlled by adjusting the pH level of the slurry. The possible explanation for this is that increasing or decreasing the pH level changes the amount of ions available in the slurry, which affects the charge in the double layer.

 

Colloid and suspension stability is important for not only polishing slurries, but also for paints, pharmaceuticals, food and beverages that have fine particles dispersed in fluids. Zeta potential can be used in these colloidal and suspension systems’ dispersion control, stability and shelf life studies.

 

ASTM Number Title Website Link
E2865-12 Standard Guide for Measurment of Electrophoretic Mobility and Zeta Potential of Nanosized Biological Materials Link
E1470-92 Standard Test Method for Characterization of Proteins by Electrophoretic Mobility Link

 

ISO Number Title Website Link
13099 Colloidal systems– Methods for zeta potential determination Link
15900 Determination of particle size distribution– Differential electrical mobility analysis for aerosol particles Link