Non-equilibrium Helmholtz free energy

That is, at any pressure the non-equilibrium Helmholtz free energy per unit mass of polymer is independent of pressure and is allowed to vary only with T, V and Fi, just as Ae equilibrium Helmholtz free energy function since the equilibrium conditions are obtained when p is the equilibrium pressure p, based on equation 13 one has that at any pressure p... 

It is useful to summarise the assumptions considered for the thermodynamic analysis discussed above, and the main results obtained. Based on the stress strain relationship for the glassy system in the form of equation 3, the chemical potential of a solute component in the polymeric mixture may be calculated as the derivative of the specific non-equilibrium Helmholtz free energy with respect to the moles of solute per polymer mass Yi at constant temperature, pressure and specific volume, as expressed in eqaution 12. On the other side, under the same assumption, the nonequilibrium Helmholtz free energy has a unique value at given temperature, specific volume and composition, whatever is the pressure of the system, as stated in equation 13. 

In this case, equation 14 provides a rational framework to extend existing expressions of the Helmholtz free energy from the equilibrium curve to the entire space of the non-equilibrium states of the system. Any mathematical model for the equilibrium thermodynamic properties of polymeric mixtures could be used to derive an expression for the non-equilibrium Helmholtz free energy according to the procedure described above. On the basis of statistical thermodynamic arguments. 

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