Experimental imprecision in determining the extensional viscosity of high molecular weight polyisobutylene suspensions

In this paper, the dependence of the extensional viscosity on volume fraction filler of high molecular weight high viscosity polyisobutylene (PIB) suspensions subjected to creeping flow is reported. The measurements at high volume fraction filler (diameter equal or bigger than 0.45) are complicated by the presence of an apparent yield stress, below which steady state flow could not be achieved. The experimental precision characteristic of these creep measurements is compared to that of other measurement techniques. Despite the nearly idealized nature of the creep experiments reported here, the experimental precision was no better than that of other measurement techniques, suggesting that this imprecision is primarily due to the complex material response. A description of our experiments and interpretation of the data is provided in the following sections.