Cohan Mechanism

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The Cohan mechanism, also known as the Cohan theory of capillary condensation, describes the condensation of liquid in a cylindrical pore. The Cohan mechanism states that on adsorption, pores do not fill vertically, but instead fill radially. This it thought to explain the hysteretic behavior seen in the adsorption-desorption process for porous materials.


For a given pore radius r, adsorption with radial capillary condensation occurs at

<math>p_{adsorption} = p_0 exp (-\sigma * v_m / rRT) </math>

whilst for desportion,

<math>p_{desorption} = p_0 exp (-2\sigma * v_m / rRT) </math>

Radial filling of pores during adsorption (left) and desorption (right) as explained by the Cohan Mehanism