Direct comparison of equibiaxial elongational viscosity measurements from lubricated squeezing flow and the MultiAxiales Dehnrheometer

We present the first direct comparisons of rheological data from the lubricated squeezing flow (LSF) technique and the MultiAxiales Dehnrheometer (MAD) instrument developed by Meissner and coworkers (J Rheol 47:989-1010, 2003). Comparisons of transient equibiaxial elongational viscosity are carried out at strain rates well into the nonlinear regime on low-density polyethylene and polystyrene melts. We find data obtained using LSF deviate from the MAD data when the Hencky strain reaches a value of approximately 1, which we interpret as a failure of the LSF technique. The strain at which the LSF technique fails is relatively insensitive to experimental parameters including strain rate. For Hencky strains larger than 1, LSF data display behavior that could easily be mistaken for the phenomenon of strain hardening.