A critical assessment of the Jastrzebski interface condition for the capillary flow of pastes, foams and polymers

This paper presents a review of unusual apparent slip effects in capillary flow rheometry. Many cases of paste, foam and polymer capillary flow have been reported where the classic analysis of Mooney has yielded unviable flow curves and apparent slip velocities; often the analysis of Jastrzebski has been used as an alternative and sometimes as the analysis of first choice. It is shown that the recently developed Tikhonov regularization method of Mooney analysis can be used to yield viable results for some of the cases where the classic Mooney analysis could not. All of the problematic foam and polymer results found in the literature were resolved, as well as some of the problematic paste results. It is shown that the use of the Jastrzebski interface condition, relating apparent slip to capillary radius, yields incorrect flow curves and apparent slip velocities. It is proposed that further research is required to understand the capillary flow of paste which does not conform to the classic Mooney analysis. In the absence of any physical grounding for the Jastrzebski interface condition, it is recommended that it should no longer be used.