Activity coefficient Flory-Huggins polymer solution

Flory-Huggins polymer solution activity coefficients. When the molecules of one component are much larger than the molecules of the other components in the mixture (i.e., polymers in solvents), the assumption of = 0 may not be appropriate. For such systems it is found that may be assumed to be zero since is assumed to be zero (i.e., 0). From - TS, then = -TS assuming = 0. On... 

Although the Wilson activity coefficient model has proven to be useful for solutions of small molecules, it has seen very limited use for polymer solutions most likely because of its increased complexity relative to the Flory-Huggins equation. 

This method is to be used to estimate the activity coefficient of a low molecular weight solvent in a solution with a polymer. This procedure, unlike the other procedures in this chapter, is a correlation method because it requires the Flory-Huggins interaction parameter for the polymer-solvent pair which must be obtained from an independent tabulation or regressed from experimental data. In addition, the specific volumes and the molecular weights of the pure solvent and the pure polymer are needed. The number average molecular weight of the polymer is recommended. The method cannot be used to estimate the activity of the polymer in the solution. 

Once the analytical expression for AGmix is known, the calculation of chemical potentials and other thermodynamic functions (activities, activity coefficients, viriai coefficients, etc.) is straightforward. For polymer solutions, we must apply Eq. (3.3) to Flory-Huggins equation (3.45), keeping in mind that volume fractions [Pg.122]

Classical polymer solution thermodynamics often did not consider solvent activities or solvent activity coefficients but usually a dimensionless quantity, the so-called Flory-Huggins interaction parameter % is not only a function of temperature (and pressure), as was evident from its foundation, but it is also a function of composition and polymer molecular mass. As pointed out in many papers, it is more precise to call it %-function (what is in principle a residual solvent chemical potential function). Because of its widespread use and its possible sources of mistakes and misinterpretations, the necessary relations must be included here. Starting from Equation [4.4.1b], the difference between the chemical potentials of the solvent in the mixture and in the standard state belongs to the first... 

Figure 5.22 Calculated activity coefficients of the monomer and resulting system pressures as a function of the weight fraction of the polymer for a polymer solution using the Flory-Huggins equation,...

The FH model for the activity coefficient, proposed in the early 1940s by Flory and Huggins, is a famous Gibbs free energy expression for polymer solutions. For binary solvent-polymer solutions and assuming that the parameter of the model, the so-called FH interaction parameter x,2, is constant, the activity coefficient is given by the equation ... 

The Flory-Huggins solute-polymer interaction parameter may be also calculated from activity coefficients [16,39]. In the case of pure solvents the equation is ... 

At this point, mention should be made of the reversed-flow gas chromatography technique, a version of IGC that has been applied successfully to the measurement of activity coefficients in polymer solutions [78], and also for determining Flory-Huggins interaction parameters and solubility parameters in polymer-solvent systems [79]. 

Solution activity data obtained by osmometry on dilute solutions showed that the second virial coefficient is dependent on molar mass, contradicting the Flory-Huggins theory. These problems arise from the mean-field assumption used to place the segments in the lattice. In dilute solutions, the polymer molecules are well separated and the concentration of segments is highly non-uniform. Several scaling laws were therefore developed for dilute (c < c is the polymer concentration in the solution, c is the threshold concentration for molecular overlap) and semi-dilute (c > c ) solutions. In a good solvent the threshold concentration is related to molar mass as follows ... 

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