Pore size distribution

Optimize materials with detailed pore size distribution analyses

What is pore size and pore size distribution?

Pore size refers to the diameter of the void spaces within a material. These pores can range from nanometers to micrometers and are a critical to the performance of materials like membranes, catalysts, adsorbents, ceramics, and battery components.

Pore size distribution describes the range and volume filled through different pore sizes within a material. It provides a comprehensive profile showing how many pores fall into specific size ranges.

Both pore size and distribution are key parameters that influence how a material behaves in real-world applications. Accurate measurement and control enable better material design, consistent performance, and improved process outcomes.

Applications

  • Catalysts and adsorbents: smaller pores increase surface area, boosting reaction sites and thus rates and capture efficiency, but can also slow analyses by limiting diffusion; therefore, there are optimal sizes for catalysts
  • Ceramics: structural integrity is influenced by the size and distribution of pores
  • Membranes and filters: selectivity and flow rate are impacted by the pore structure
  • Batteries and fuel cells: pore networks govern the movement of ions and gases, affecting charge/discharge rates and energy efficiency
  • Pharmaceuticals: pore size and surface area impact drug delivery, API loading capacity, and product stability

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How to calculate pore size distribution

Several techniques are used to measure pore size distribution. In many cases, combining techniques gives the most complete picture of pore size distribution and material behavior.

Gas adsorption measures the amount of gas adsorbed at different relative pressures; models such as Barrett-Joyner-Halenda (BJH) and Density Functional Theory (DFT) are used to derive pore size distribution.

  • Typical Pore Range: 0.3 - 50 nm (micropores to mesopores)
  • Best for: high surface area powders, Metal-Organic Frameworks (MOFs), Covalent organic frameworks (COFs), zeolites, activated carbons

In mercury intrusion porosimetry, mercury is forced into the pore under pressure; the Washburn equation is used to infer pore size based on the volume intruded at each pressure.

  • Typical Pore Range: 3 - 1000 µm (mesopores to macropores)
  • Best for: broad distributions including large pores, rigid solids (ceramics, catalysts, tablets)

Capillary flow porometry measures the pressure needed to displace a wetting liquid from through-pores; it differentiates between the smallest and largest flow paths.

  • Typical Pore Range: 0.02 - 500 µm (through-pores)
  • Best for: membranes, separators, filters

Imaging techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) provide direct visualization of 2D or 3D pore structures.

  • Typical Pore Range: resolution-dependent
  • Best for: supplementing quantitative methods

Liquid-liquid porometry measures the pressure needed for one liquid to displace another liquid from pores.

  • Typical Pore Range: 20 nm - 1 µm
  • Best for: hydrophilic or hydrophobic membranes

Instruments for pore size analysis

Micromeritics AutoPore V

Density and porosimetry analysis for mesoporous and macroporous materials
Micromeritics AutoPore V

Micromeritics AccuPore

The easiest, most accurate and versatile measurement of through-porosity
Micromeritics AccuPore