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 osc illatory flow, step strain, step-shear rate and steady shear using a R heometrics RDSII rheometer. The time dependence represented as a discr ete spectrum of relaxation times and the strain dependence characteriz ed as an exponential damping function have been presented as a functio n of PIB concentration. The relaxation spectrum was calculated from th e dynamic storage modulus and loss modulus. The damping function was d etermined from the non-linear relaxation modulus in a step-strain expe riment. The Wagner integral viscoelastic model incorporated with the r elaxation and the damping function has been used to predict the stress growth and the steady-shear behaviour, which were compared with the e xperimental data. A novel extensional rheotester was also used in this study to measure the stretching response of polymer solutions. The da ta gave a near single relaxation time for each solution, and this sing le relaxation time obtained from uniaxial extension was correlated to the relaxation spectrum obtained in simple shear.