THE RHEOMETRY OF SOLUTIONS OF POLYISOBUTYLENE IN A MIXED-SOLVENT

This paper is concerned with the rheometrical characterization of a fa mily of liquids based on the S1 fluid which is currently the object of an international research programme. The programme has, as primary ob jective, the study of how a solvent influences the rheological propert ies of a polymer solution for as broad a range as possible of the solv ent concentration. S1 is a specific solution of polyisobutylene (PIB) in a solvent which consists of a mixture of polybutene oil and Decalin . In this paper, a family of solutions having different concentrations of PIB is studied. Conventional rheometrical data is presented for th e solutions and these are fitted to useful but relatively simple equat ions. Although the usual limiting relationships that are expected for continuous media are shown to be satisfied, the empirical Cox-Merz rul e is found to be violated. The characterization was complicated by the occurrence of an apparent shear-thickening phenomenon which was studi ed in detail and explained. Also, the now familiar instability that of ten occurs in rotary shear flows was shown to occur, as expected, at t he same Deborah number for each of the solutions studied.