Following the IUPAC recommendation, the pore space in porous materials is divided into three groups according to the pore size diameters: macropores of widths greater than 50 nm, mesopores of widths between 2 and 50 nm and micropores of widths less than 2 nm. Zeolites, activated carbon, tight rocks, cement paste or construction materials are among these materials. In recent years, a major attention has been paid on these microporous materials because the surface-to-volume ratio (i.e., the specific pore surface) increases with decreasing characteristic pore size. These materials can trap an important quantity of fluid molecules as an adsorbed phase. This is important for applications in gas storage, gas separation, petroleum and oil recovery, catalysis or drug delivery.

For these microporous materials, a deviation from standard poromechanics is expected. In very small pores, the molecules of fluid are confined. Fluid-fluid and fluid-solid interactions of molecules are modified and this effect may have significant consequences at the macroscale, such as instantaneous swelling deformations. In different contexts, these deformations may be critical. Generally, natural and synthesized porous media are composed of a double porosity: the microporosity where the fluid is trapped as an adsorbed phase and a meso or a macro porosity required to ensure the transport of fluids to and from the smaller pores. If adsorption in nanopores induces instantaneous deformations at a higher scale, the matrix swelling may close the transport porosity, reducing the global permeability of the porous system or annihilating the functionality of synthesized materials.