Viscosity-Temperature Relations and Thermodynamic Parameters

In order to achieve a quantitative separation of the factors responsible for the temperature coefficient of the intrinsic viscosity, K should first be established as a function of temperature by carrying out measurements in -solvents having s covering the temperature range of interest. The expansion factor may then be obtained from the intrinsic viscosity measured at the temperature T in the given solvent. If Cm occurring in Eq. (10) were independent of the temperature, — should then plot linearly with 1/T, However, 

If we now calculate Cm from Eq. (7), the results of the foregoing analysis yield numerical values for the entropy of dilution parameters ypi in the various solvents. From the 0 s obtained simultaneously, the heat of dilution parameter Ki — 0 pi/T may be computed. To recapitulate, the value of in conjunction with gives at once Cm i(1--0/T). Acceptance of the value of Cm given by Eq. (7) as numerically correct makes possible the evaluation of the total thermodynamic interaction i(l —0/7 ), which is equal to ( i—/ci). If the temperature coefficient is known, this quantity may be resolved into its entropy and energy components. 

Thermodynamic parameters deduced as described above are shown in Table XLI for polyisobutylene and for polystyrene. It will be recalled that these primary parameters are obtained only with consider- 

It will be observed that entropies of dilution (as indicated by i) are highly variable from one system to another. This is contrary to the theory developed from consideration of lattice arrangements, according to which pi should be approximately 1/2 and nearly independent of the system. For polystyrene in methyl ethyl ketone, the entropy of dilution is nearly zero i.e., this solvent is a poor one not because of an adverse energy of interaction but because of the low entropy. First neighbor interactions apparently contribute to the entropy as well as to the energy, a point which was emphasized in Chapter XII. It will be noted also that cyclic solvents almost without exception are more favorable from the standpoint of the entropy than acyclic ones. 

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