Polanyis theory for micropore adsorption

Microporous materials exhibit type 1 isotherms since the size of the pores restricts adsorption into a few layers. The Held strength within the pores is so great that it is difficult to determine whether the adsorbate packs as a liquid or in a more condensed form. Polanyi [51] assumed that above the critical temperature the adsorbate can adsorb only as a vapor whose density increases as it approaches the surface around the critical temperature the vapor near the surface starts to liquefy, and substantially below the critical temperature the adsorbate completely liquefies. Under this final condition, the adsorbed volume of liquid (v) can be determined from the adsorption isotherm. Polanyi potential theory states that the adsorption potential for adsorbate in the liquid state is given by the isothermal work required (e) to compress the vapor from its equilibrium pressure (P) to its saturated vapor pressure 

Niemark [52] stated that the Polanyi theory of adsorption was gaining widespread acceptance due to the clarity of the underlying assumptions and the ensuing thermodynamic relationships. 

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