where w 11 and w 22 denote the interaction energy between neighboring species of likewise molecules and w 12 between different molecules. The total number of such contacts can be written as zN 2 φ 1 = zN 1 φ 2 where z is the assumed coordination number of surrounding molecules around a molecule from regular solution theory 19 . The resulting enthalpy change for each of these contacts can be written as ∆H m = zN 1 φ 2 ∆w with the Flory-Huggins interaction parameter 50