Understanding the Zeta Potential of Nanoparticles

Colloidal Stability of Nanoparticles: Why Zeta Potential is Important?

Due to their extended surface to volume fraction, nanoparticles are pronouncedly affected by the electrostatic stabilisation mechanisms as compared to larger objects. Zeta potential is a critical factor in determining the colloidal stability of particles. It is an accessible measure of the magnitude of the repulsive forces between nanoparticles caused by thrie charge in an electrolyte medium. A high absolute value of Zeta potential indicates strong repulsion between particles, which helps preventing aggregation and maintains colloidal stability or adhesion on other available surfaces.

 

What is Zeta Potential of Nanoparticles?

Zeta potential is the electric potential difference (voltage) between the bulk of the colloidal suspension medium and the slipping plane of a particle. The slipping plane describes an imaginary boundary that separates the layer of electrolyte adhered to the surface of a particle from the freely moving bulk of the liquid. For nanoparticles Zeta potential plays a crucial role in achieving colloidal stability. The relationship between particle size and Zeta potential is significant because as the radius of nanoparticles decreases, the surface area to volume ratio increases due to its quadratic and cubic radius dependencies. This makes Zeta potential more influential as probability is a function of accessible surface.

 

How to Measure Zeta Potential?

Zeta potential can be measured using various techniques, the most common methods include:

Electrophoretic Light Scattering (ELS):

• How It Works: Measures the movement of charged particles in an alternating electric field by analyzing the Doppler shift of scattered laser light.

• Applications: Ideal for small particles and provides rapid, precise measurements.

Streaming Potential Methods:

• How It Works: Involves flowing an electrolyte solution through a porous or capillary cell, measuring the potential generated as the liquid moves relative to charged surfaces.

• Applications: Suitable for evaluating interactions at solid surfaces and membranes.

Microelectrophoresis:

• How It Works: Observes individual particles under a microscope while applying an electric field, tracking their velocity to determine Zeta potential. This can also be applied to nanoparticles in NTA (Nano Tracking Analysis)

• Applications: Useful for direct observation and low sample volumes, also to directly observe particle interactions to other colloidal structures, such as proteins.

To ensure accurate and comparable results, standardized controls are crucial. Applied Microspheres offers Zeta Potential Controls, which serve as benchmark references for both electrophoretic mobility and streaming potential methods. These controls facilitate the calibration and validation of measurement instruments, enhancing the precision of your Zeta potential data. Applied Microspheres Zeta Potential Controls are traceable to certified reference materials. Due to the absence of surfactants, they provide direct insight on the charge properties cause by charged groups on the particle surface only.

 

pH Dependence of Zeta Potential

The Zeta potential of particles is highly sensitive to the pH and the ionic strength of the surrounding medium, which leads to compression or de-compression of the electric double-layer surrounding any charged colloid in an electrolyte solution. Changes in pH can alter the ionization of surface groups on particles, thereby modifying their surface charge. Both effects go hands in hands.

Low pH (Acidic Conditions):

Can increase positive Zeta potential as more protons (H⁺) attach to the particle surfaces.

High pH (Basic Conditions):

Can enhance negative Zeta potential by deprotonating surface groups, leading to more negative charges.

Understanding the relationship between pH and Zeta potential is essential for optimizing conditions to achieve desired stability in various applications. To enable constant and reliable determinations of the Zeta potential, Applied Microspheres Zeta Potential Controls are buffered at their optimal pH value.

 

Typical Zeta Potential Ranges for Nanoparticles

Zeta potential values are key indicators of the stability of colloidal suspensions.

High absolute values (typically above +30 mV or below -30 mV) suggest that particles possess strong repulsive forces, which help keep them well-dispersed and prevent aggregation.

Moderate values (between +30 mV and -30 mV) indicate weaker repulsion, increasing the likelihood of particle clumping and potential instability in the suspension.

Low absolute values (close to 0 mV) imply minimal repulsive forces, making the system prone to significant aggregation and destabilization.

Moderate and low Zeta potentials lead to an essential need to apply further stabilization mechanisms, such as steric hindrance, to prevent particle aggregation.

 

Possible Applications of Zeta Potential and Zeta Potential Controls

Zeta potential is used in various applications, including water treatment, where it helps in predicting and controlling particle behavior in aqueous environments. By adjusting Zeta potential, it is possible to enhance the effectiveness of processes like coagulation and flocculation.

In any technical application of nanoparticles, where adhesive forces need to be prevented or are desired (such as ink industries), perfect control of the Zeta potential is essential.

In biomedical applications the Zeta potential is the primary observable to get insight on interactions between functional particles and a potential linker. Desired chemical interactions between functional groups request for control of the Zeta potential. Both specific and unspecific binding of molecules on particles, for instance for desired removal of undesired molecules in the medium, can only take place when the Zeta potential conditions are chosen suitably.