The fluid-solid interaction contributed to isosteric heat is greater than the contribution of fluid-fluid interaction, because at low adsorption loading, water molecules initially adsorbed at the functional groups and this leads to the greater fluid-solid interaction, after that the opposite is true. While the FS253K is still greater than the FS273, but heat of adsorption at both temperatures are close to each other. Therefore water molecules adapt themselves to have the adsorbed heat close to the heat of liquefaction by decreasing the fluid-fluid interaction.