This conclusion is a consequence of the high jet speeds and small nozzle diameters in combination with the relatively high viscosity solvent and modest molecular weights of the polystyrene, which results in high Weissenberg numbers and moderate values of the extensibility, L studied here. As discussed in earlier papers [3,6], other jetting fluid combinations, such as those of de Gans et al. [4], lie in a different jetting regime where full extension does not occur and relaxation time controls the viscoelastic behaviour. Consequently inkjet fluid assessment methods need to provide a full characterisation including both linear and nonlinear viscoelastic properties. This complexity suggests assessments of inkjet fluids might have to include jetting from sets of DoD print head devices with different sensitivities to all the various VE parameters [37], rather than reliance on testing without jetting. This was not the expected outcome from the present work but does echo the very pragmatic viewpoint expressed as a “map of misery” by Clasen et al. [38] and may provide a way forward for future R&D strategies towards ink testing.
