Electrical double layer and zeta potential

Explain Electrical double layer and zeta potential | Factors Influencing Electrical Double Layer Formation

What are Electrical double layer and zeta potential? Discuss the factors which affects the Formation of Electrical Double Layer.

Electrical double layer

Electrical double layer is the region near a charged surface where potential difference exists due to the presence of ions. It consists of two layers, the inner Helmholtz layer and the outer Helmholtz layer. The layer of ions attracted to the charged surface, which creates an electric field is inner Helmholtz layer, and the outer Helmholtz layer is a layer of ions attracted to the inner Helmholtz layer, forming a counter-charge layer.


Electrical double layer zeta potential

Formation of the electrical double layer can be explained by the Gouy-Chapman-Stern theory (GCS Theory), which states that when a charged surface is immersed into an electrolyte solution, ions from this solution will be attracted towards this surface and will produce an ionic compact layer on it. This layer of ions is pushed back by the repulsive forces between ions, creating a diffuse layer. The combination of both compact and diffuse parts forms Stern Double Layer also called Electrical Double Layer.
The thickness of this layer depends on various factors such as ionic strength of the solution, surface charge density and size of its ions. The diffused double-layer thickness (d) was calculated by Gouy using Debye-Huckel theory in 1909.


Zeta Potential

Zeta potential is the potential difference between the surface of the charged particle and the surrounding fluid. It is an important parameter to measure the surface charge of colloidal particles and is also used to predict the stability and behavior of colloidal systems. The zeta potential is affected by factors such as pH, temperature, and the presence of other ions in the solution.

Keeping the total concentration of the electrolyte constant, increases the amount of electrolytes or increasing the valency of the counter ions, decreases the Stern and Zeta potentials owing to the decrease in thickness of the double layer. Zeta potential acts as an energy barrier for the stability of colloids and suspensions.

Zeta potential determines the degree of repulsion between adjacent, similarly charged dispersed particles and therefore, has practical applications in the stability of systems containing dispersed particles.

Zeta potential cannot be measured directly. Zeta potential can be measured by using techniques like electrophoresis, where an electric field is applied to the charged particles, and their movement is recorded. The magnitude and direction of the particle's movement can give valuable information about the zeta potential and surface charge.


Factors Influencing Electrical Double Layer Formation

The formation of an electrical double layer is a complex and dynamic process that is influenced by several factors. These factors play a crucial role in determining the properties and behavior of the double layer. Some important factors that influence the formation of the electrical double layer are discussed below-/

Nature of the Electrolyte Solution

Some electrolytes are like social butterflies, bringing lots of ions to the party and thickening the electrical double layer. Others are loners, barely stirring things up. The type and concentration of electrolytes can greatly influence the double layer's behavior.

Charge Density of the Surface

The charge density of the solid surface is the primary factor that determines the formation of an electrical double layer. A higher charge density of the surface, stronger the interaction with the ions in the solution, leading to a thicker and more stable double layer because a higher charge density creates a larger electric field which in turn, attracts more ions to the surface.

Electrolyte Concentration

The concentration of electrolyte in the solution also has a significant influence on the formation of the electrical double layer. Higher concentration of electrolyte increases the number of ions in the solution makes a thicker double layer because the excess ions in the solution are attracted to the surface, forming a dense and compact layer.

Charge of the Ions

The charge of the ions in the solution is another important factor that affects the formation of the electrical double layer. It is known as the ionic strength of the solution and is determined by the concentration of charged particles in the solution. Higher the charge on ions, stronger the interaction with the surface and creates a thicker and more stable double layer.

Nature of the Solid Surface

The specific nature of the solid surface, such as its material composition and surface roughness, also plays a role in the formation of the electrical double layer. Different surface materials have different affinities for different ions, resulting in different charge densities and electric fields. The surface roughness also affects the stability of the double layer, with a rougher surface often leading to a less stable double layer.


Temperature

Temperature is another critical factor that affects the formation of electrical double layer. Increases the temperature, increases the mobility of ions, leading to a thicker and more diffuse (less compact) double layer.
Temperature also affects the viscosity of the solution, which changes the thickness of the double layer.

Presence of Adsorbed Species

The presence of adsorbed species on the solid surface can affect the formation of the electrical double layer. Adsorbed molecules can form a barrier, reducing the interaction between ions and the surface. This can result in a thinner double layer, reducing the electrical capacity of the interface.

Electrical double layer and zeta potential MCQs

Correct statement about Helmholtz electrical double layer is

I. It is a combination of two layer of similar charges around colloidal sol.
II. It is a combination of two layers of opposite charges around the colloidal sol.
III. In it 1st layer of ions is diffused while 2nd layer of ions is fixed.
IV. The potential difference the fixed layer and the diffused layer is called zeta potential.

A. I and II
B. I and III
C. II and IV  
D. III and IV

Zeta potential (or electrokinetic potential) is the

A. potential required to bring about coagulation of a colloidal sol
B. potential required to give the particles a speed of 1 cm/s in the sol
C. potential difference between fixed charged layer and the diffused layer having opposite charge  
D. potential energy of the colloidal particles

Measuring Zeta potential is useful in determining which property of colloidal solution?

A. Stability of the colloidal particles  
B. Size of the colloidal particles
C. Viscosity
D. Solubility