Sorption on deformable solids. Density functional theory approach.

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Understanding fluid-solid interactions is crucial for catalysis, separation, and storage.
• Existing models often assume uniform solid density, limiting accuracy near interfaces.
• Describing systems with both fluid and solid phases requires advanced theoretical frameworks.

Purpose of the Study:

• To develop a modified density functional theory (DFT) for fluid adsorption and absorption by solids.
• To model systems where the solid's density is non-uniform, particularly near interfaces.
• To predict how fluid density variations affect solid density and vice versa.

Main Methods:

• Proposed a modified density functional theory (DFT) approach.
• Treated the fluid component using a grand canonical ensemble.
• Modeled the solid component as a canonical ensemble with a fixed number of molecules.
• Obtained solid density distribution by minimizing a thermodynamic potential, avoiding a priori assumptions.

Main Results:

• The theory predicts intrinsic changes in solid density near the interface, independent of the fluid.
• It shows solid density variations in response to changes in the external fluid density.
• Non-uniform solid density was found to damp oscillations in fluid density, unlike uniform solids.
• The model quantifies both adsorbed and absorbed fluid amounts.

Conclusions:

• The modified DFT accurately describes fluid adsorption and absorption in systems with non-uniform solid densities.
• This approach provides a more realistic representation of fluid-solid interfaces.
• The findings have implications for designing materials for gas storage, separation, and catalytic processes.