Elongation and subsequent relaxation measurements on dilute polyisobutylene solutions

The elongation and subsequent relaxation of dilute polyisobutylene solutions in mixtures of polybutene and kerosine and in mixtures of polybutene and toluene have been investigated using an extensional rheometer based on the principle of droplet stretching. Single exponential stretching functions have been applied and the resulting non-idealities of the experiment will be addressed. The results show that the transient Trouton ratio for different values of the applied axial extension rate between 1 and 6 s(-1) scales with the strain for values larger than 3. The magnitude of non-ideal stretching effects on the Trouton ratio for strain values up to 3 is found to be fairly small. For strains larger than 5.5 the onset of steady-state values of the extensional viscosity is found, but true steady-state values are not obtained below the maximum strain of 7.2. The measurements provide an indication for increasing plateau values with increasing concentration and with increasing molecular weight of the polymer. The results also show that the relaxation after stretching up to a specific axial strain value with different extension rates scales with the product of the extension rate at the start of the relaxation process and the time.