Beware of CaBER: Filament thinning rheometry does not always give ‘the’ relaxation time of polymer solutions

Abstract

We show that the apparent relaxation time inferred from the exponential thinning regime in viscoelastic pinch-off is not necessarily a material property, as was assumed so far, but depends on the system size for various polymer solutions and filament thinning techniques. It depends on the plate size in Capillary Breakup Extensional Rheometry (CaBER) with both slow and fast plate separation protocols, and on the nozzle size in Dripping-onto-Substrate (DoS), corroborating recent observations with the dripping technique. It is not due to artifacts such as solvent evaporation or polymer degradation and it cannot always be rationalized by finite extensibility effects.