Determination of the Zeta potential of the silica suspension


Nanoscale silicon dioxide is extremely versatile. When polishing the semiconductor surface, nanoscale silicon dioxide can be used as an abrasive in addition to being used as a coating material due to its excellent surface performance.

The compound improves reinforcement, shear strength, thixotropy, etc., and therefore can be widely applied in steel, plastic, rubber and solar energy fields.

Image credit: Bettersize Instruments Ltd.

Thanks to recent developments in the field of chemistry, in 1968 Stober discovered that nano-silica the spheres, which have a particle size approximately close to monodisperses, can be obtained at ambient temperature. This is achieved by stirring a mixture of ammonia in different proportions with tetramethylsilane dispersed in a solution of ethanol.

In many applications, it is necessary for the nano-silica to be dispersed in a liquid. The measurement of the zeta potential is therefore essential, in order to deepen the understanding of the stability of the system and to improve the quality and consistency of the product.

The BeNano 180 Zeta nanoparticle size and zeta potential analyzer from Bettersize was used in this process to measure the zeta potential of nano-silica as it is obtained from different batches dispersed in the aqueous medium.

Theory and Instrumentation

the Bettersize BeNano 180 Zeta is equipped with a solid-state laser, which has a wavelength of 671 nm and a light source power of 50 mW. Charged particles are driven to electrophoresis by applying an electric field to the sample.

The frequency of the shift of the scattered light from the origin is due to the electrophoretic motion of the particles at the point at which the laser irradiates the sample. An APD (avalanche photodiode detector) is used to collect the scattered light signals at 12°.

Through the use of Phase Analysis Light Scattering (PALS) technology, the zeta potential of samples, even at low electrophoretic mobility, can be detected by the BeNano 180 Zeta.

Experience

The zeta potential of four samples of nano-silica slurry was measured in two states – both at its original concentration (with 10% solids content) and at a state of 30-fold dilution in water .

To ensure the repeatability of the result and to obtain its standard deviation, each sample was measured at least three times.

Results and discussion

The zeta potentials of four nanoscale silica suspensions are obtained using PALS Technology. The phase plot of each measurement is shown in Figures 1-4, the slope of which correlates with the frequency shift caused by electrophoresis. Each phase plot shows a clear slope and demonstrates a good signal-to-noise ratio, as shown in the figures.

The phase diagram and trend of the zeta potential of sample 1# with the original concentration (left) and diluted 30 times (right)

Figure 1. The phase diagram and trend of the zeta potential of sample 1# with the original concentration (left) and diluted 30 times (right). Image credit: Bettersize Instruments Ltd.

The phase diagram and trend of the zeta potential of the 2# sample with the original concentration (left) and diluted 30 times (right).

Figure 2. The phase diagram and trend of the zeta potential of the 2# sample with the original concentration (left) and diluted 30 times (right). Image credit: Bettersize Instruments Ltd.

The phase diagram and trend of the zeta potential of the 3# sample with the original concentration (left) and diluted by 30 times (right)

Picture 3. The phase diagram and trend of the zeta potential of sample 3# with the original concentration (left) and diluted 30 times (right). Image credit: Bettersize Instruments Ltd.

The phase diagram and trend of the zeta potential of the 4# sample with the original concentration (left) and diluted 30 times (right).

Figure 4. The phase diagram and trend of the zeta potential of the 4# sample with the original concentration (left) and diluted 30 times (right). Image credit: Bettersize Instruments Ltd.

As shown, zeta potentials are negative, which displays a negative charge on the surface of the particles. The excellent reproducibility of the results is demonstrated by the consistent trends in the zeta potential as well as the relatively low standard deviations.

Samples are less likely to form aggregates, since the zeta potentials of all samples are high (>30 mV). It can therefore be concluded that the 1# sample and the 2# sample have the highest zeta potentials, followed by the 3# sample and the lowest 4# sample.

It clearly appears that the 1# and 2# samples are the most stable among the four silica suspensions. Moreover, after being diluted 30 times, the 2# and 3# samples have much higher absolute values ​​of zeta potentials, which indicates better stabilities than those of the stock solutions.

Table 1. The results of the zeta potential of the silica samples. Source: Bettersize Instruments Ltd.

To taste Zeta potential
(stock solution) (mV)
Zeta potential
(30-fold dilution) (mV)
1# -55.08±1.18 -52.48±0.56
2# -43.90±1.2 -50.85±0.64
3# -35.98±1.07 -45.22±0.50
4# -33.40±0.77 -37.52±0.56

conclusion

The BeNano 180 Zeta was used to take Zeta potential measurements of four nano-silica suspensions, both at high concentration and diluted 30 times with pure water.

Good repeatability is shown in the results, allowing stability comparison between different formulations or batches to enable product quality control and monitoring.

This information has been extracted, reviewed and adapted from materials provided by Bettersize Instruments Ltd.

For more information on this source, please visit Bettersize Instruments Ltd.

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