The tensile behaviour of elastic liquids under dynamic stressing

We report measurements of the tensile strength, F-c, of dilute polymer solutions, involving tension pulses of ca. 200-300 mu s duration, and stressing rates of ca. 1-10 bar/mu s: Contrary to previous indications in the literature, the tensile strength of polyacrylamide (PAA) solutions under pulsed dynamic stressing is found to increase with increasing polymer concentration. This accords with the results of a study of the effect of PAA concentration on the development of liquid jets, which are formed by bubble collapse in dilute PAA solutions: a marked reduction in jet length and velocity is found due to the presence of PAA. Estimates of the tensile stresses supported by the stretching jets are commensurate with the results obtained in measurements of F-c. (C) 2000 Elsevier Science B.V. All rights reserved.