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Pore Size Adsorption And Absorption Techniques

Updated: Dec 15, 2023

Pore size testing is a critical procedure used in various industries, including materials science, pharmaceuticals, and environmental engineering. It helps determine the size and distribution of pores in a material, which is vital for understanding its properties and performance.

During pore size testing, two key processes come into play: adsorption and absorption. In this blog, we'll delve into the differences between adsorption and absorption, their significance in pore size testing, and the methods commonly employed to study these processes.

What is Adsorption?

adsorb gases

Adsorption refers to the process by which molecules or particles are attracted and accumulate on the surface of a solid material. This occurs due to weak interactions between the material's surface and the molecules of the adsorbate.

These interactions can be physical (van der Waals forces) or chemical (chemisorption) in nature.

In the context of pore size testing, adsorption is commonly used to investigate the pore size distribution of materials with porous structures, such as zeolites, activated carbon, and molecular sieves. The technique most frequently employed for adsorption studies is the Brunauer-Emmett-Teller (BET) method.

The BET Method:

BET method showcasing gas molecules

The BET method is based on the principle of multilayer adsorption. It assumes that gas molecules form layers on the surface of the material until a monolayer is reached. The BET equation relates the quantity of adsorbed gas to the pressure of the gas and the properties of the gas and the material's surface.

By analyzing the adsorption isotherm obtained from the BET experiment, scientists can calculate the specific surface area and pore size distribution of the material.

What is Absorption?

penetration and diffusion of a substance (gas or liquid) into the bulk of a solid or liquid material

Absorption, on the other hand, involves the penetration and diffusion of a substance (gas or liquid) into the bulk of a solid or liquid material.

Unlike adsorption, which occurs on the material's surface, absorption takes place throughout the material's volume.

Absorption is not typically used in pore size testing because it does not provide information about the material's surface area or pore size distribution. Instead, it is more relevant for understanding how substances interact with materials at a molecular level and how they can be incorporated or dissolved into the material's structure.

Importance of Pore Size Testing

cross-section of a porous material

Pore size testing is of great importance across various industries due to its direct impact on material properties and performance.

For instance:

  1. Catalysts: In the chemical industry, pore size testing is crucial for developing efficient catalysts. Catalysts with well-defined pore structures can enhance reaction rates by providing more active surface area for reactants to adsorb and undergo chemical transformations.

  2. Adsorbents: In gas separation processes, such as natural gas purification and air filtration, materials with specific pore sizes are employed to selectively adsorb certain gases, allowing the desired components to pass through.

  3. Drug Delivery: In pharmaceuticals, pore size testing plays a vital role in developing drug delivery systems. Pore size influences drug loading capacity, release rate, and stability.

Techniques for Pore Size Testing

pore size testing in drug delivery systems

Several techniques are available for pore size testing, including:

  1. Gas Adsorption: As discussed earlier, the BET method is commonly used to determine the surface area and pore size distribution of porous materials.

  2. Mercury Intrusion Porosimetry: This method involves measuring the intrusion of mercury into the pores of a solid material under varying pressure. It provides information on both micropores and mesopores.

  3. Nitrogen Adsorption: Similar to gas adsorption, nitrogen adsorption is used for porous materials with small pores. The data obtained are utilized to calculate pore size distribution and surface area.

  4. Capillary Flow Porometry: This method measures the flow of liquid through the pores of a material. It is useful for characterizing the pore size distribution of membranes and filters.


Pore size testing is a fundamental technique employed in various industries to understand the properties and performance of porous materials. Adsorption, particularly using the BET method, plays a central role in determining the surface area and pore size distribution of these materials.

While absorption is not typically used in pore size testing, it remains vital for understanding the interaction of substances within the bulk of materials.

Understanding the differences between adsorption and absorption, and their relevance in pore size testing, allows scientists and engineers to optimize material design and tailor materials for specific applications, leading to advancements in technology and improved product performance.


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