RHEOLOGICAL CHARACTERIZATION OF THE TIME AND STRAIN DEPENDENCE FOR POLYISOBUTYLENE SOLUTIONS

The rheological response of polyisobutylene (PIB) solutions in Decalin and a related standard fluid S1 has been characterized in dynamic oscillatory flow, step strain, step-shear rate and steady shear using a Rheometrics RDSII rheometer. The time dependence represented as a discrete spectrum of relaxation times and the strain dependence characterized as an exponential damping function have been presented as a function of PIB concentration. The relaxation spectrum was calculated from the dynamic storage modulus and loss modulus. The damping function was determined from the non-linear relaxation modulus in a step-strain experiment. The Wagner integral viscoelastic model incorporated with the relaxation and the damping function has been used to predict the stress growth and the steady-shear behaviour, which were compared with the experimental data. A novel extensional rheotester was also used in this study to measure the stretching response of polymer solutions. The data gave a near single relaxation time for each solution, and this single relaxation time obtained from uniaxial extension was correlated to the relaxation spectrum obtained in simple shear.