Poly Flory interaction parameter

Before leaving the subject of interfacial behavior in polymers, it is instructive to consider the interfacial tension, and resulting interfacial density profiles. Making effective use of the Flory interaction parameter x, Helfand and Tagami (1972), Gaines (1972), Wu (1974), and others estimated the interfacial surface tension between incompatible polymer pairs (see Table 13.1). Also shown in Table 13.1 are theoretically estimated values of x-(See Section 4.7 and especially Sections 4.7.3 and 9.6 for related discussion.) Helfand and Tagami found that the characteristic thickness of the interface is proportional to x — y for small /. For a polystyrene/poly(methyl methacrylate) system, the value of / leads to an estimated interfacial thickness of 50 A. This value is much less than that estimated by Voyutskii and Vakula... 

Experimental VLE data [14] for poly (acrylonitrile-co-butadiene) and its parent homopolymers are shown in Table 6. Solvent absorption in the copolymer increases as its butadiene content rises. This rise is expected because the hydrocarbon segments of pentane are better liked by hydrocarbon segments of butadiene, whereas polar segments of acrylonitrile repulse nonpolar pentane molecules. Once again, Flory interaction parameter, x. implies that with rising acrylonitrile concentration in copolymer composition. 

Since there had not been any measurements of thermal diffusion and Soret coefficients in polymer blends, the first task was the investigation of the Soret effect in the model polymer blend poly(dimethyl siloxane) (PDMS) and poly(ethyl-methyl siloxane) (PEMS). This polymer system has been chosen because of its conveniently located lower miscibility gap with a critical temperature that can easily be adjusted within the experimentally interesting range between room temperature and 100 °C by a suitable choice of the molar masses [81, 82], Furthermore, extensive characterization work has already been done for PDMS/PEMS blends, including the determination of activation energies and Flory-Huggins interaction parameters [7, 8, 83, 84],... 

Regressed Interaction Parameters for Water-Dextran (Mn = 23,000)-Poly(ethylene glycol) (Mw = 6,750) at 273 K Using a Modified Flory-Huggins Model... 

Table 3. Flory x (x ) parameters and X12 contact interaction parameters in poly(dimethyl siloxane) at 25 °C...

Lichtenthaler et al. (55) determined interaction parameters for 22 solutes in poly(dimethyl siloxane) to test several expressions of the combinatorial entropy of mixing [Eq. (7)]. The magnitude of the interaction parameter is indeed directly dependent on the evaluation of the combinatorial contribution. The combinatorial contribution was computed following both the Flory-Huggins approximation and the multiple-connected-site model recently developed by Lichtenthaler, Abrams and Prausnitz (56). This model, which retains the Flory-Huggins term, also corrects for the bulkiness of the components of the mixture. Interaction parameters were computed through both approximations, showing the sensitivity of the results to the model chosen. 

IGC was used to determine the thermodynamic miscibility behavior of several polymer blends polystyrene-poly(n-butyl methacrylate), poly(vinylidene fluoride)-poly(methyl methacrylate), and polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends. Specific retention volumes were measured for a variety of probes in pure and mixed stationary phases of the molten polymers, and Flory-Huggins interaction parameters were calculated. A generally consistent and realistic measure of the polymer-polymer interaction can be obtained with this technique. 

Fig. 3.10. Comparison of the predictions of the equation-of-state theory (full line) with the results ( ) of experiment for the concentration dependence of the interaction parameter of poly(isobutylene) in benzene at 2S °C (after Eichinger and Flory, 1968).

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