In some paper people have subtracted cohesive energy densities of pure polymer and pure solvent from cohesive energy density of solvent polymer mixture
ΔHmix = (H/V)poly-sol - (H/V)poly- (H/V)sol
While in some other papers authors had subtracted cohesive energy density of solvent polymer mixture from cohesive energy densities of pure polymer and pure solvent
ΔHmix = (H/V)poly + (H/V)sol - (H/V)poly-sol
You have a reaction
poly +sol ↔poly-sol It is reversible
According to thermodynamics, enthalpy change during the stright reaction
ΔHmix = (H/V)poly-sol – [(H/V)poly + (H/V)sol]
For the reverse reaction will be the opposite
Best regards.
Thank you for your reply. But for calculating Flory Huggins interaction parameter from MD simulation people have used same initial configuration but have used those two opposite equations. I really unable to understand the logic behind this.
The two equations differ only in the sign of the result. In thermodynamics the sign is defined positive, if the quantity is added to the system. If you define the thermodynamic system as the left side of Yuri Mirgorods equation you have another sign than taking the right side as "system", but the absolute value is the same. With other words the sign depends on the definition of the thermodynamic "system". This should have been defined in the papers you have looked at.
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