# Difference between revisions of "Cohan Mechanism"

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.

Figure 1 shows a typical adsorption-desorption isotherm is shown for a porous solid. A hysteresis is evident, indicating that some adsorbate is retained during desorption and released at p/p0 value less than that required to cause adsorption.

$p/p0 = exp (-2\sigma * v_m / rRT)$

Isotherm for a porous solid of uniform pore radius.

$p_{adsorption} = p_0 exp (-\sigma * v_m / rRT)$
$p_{desorption} = p_0 exp (-2\sigma * v_m / rRT)$