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Recent results from a number of UK academic inkjet research studies advance the understanding of complex fluid jetting behavior and may be of interest to the wider digital fabrication community for the enhancement of inkjet printing applications.

Fluid assessment methods, requiring small volumes and avoiding the need for jetting, are particularly useful in the design of functional fluids for inkjet printing applications. With the increasing use of complex (rather than Newtonian) fluids for manufacturing, single frequency fluid characterisation cannot reliably predict good jetting behaviour, owing to the range of shearing and extensional flow rates involved. However, the scope of inkjet fluid assessments (beyond achievement of a nominal viscosity within the print head design specification) is usually focused on the final application rather than the jetting processes. The experimental demonstration of the clear insufficiency of such approaches shows that fluid jetting can readily discriminate between fluids assessed as having similar LVE characterisation (within a factor of 2) for typical commercial rheometer measurements at shearing rates reaching 104 rad s−1. Jetting behaviour of weakly elastic dilute linear polystyrene solutions, for molecular weights of 110–488 kDa, recorded using high speed video was compared with recent results from numerical modelling and capillary thinning studies of the same solutions. The jetting images show behaviour ranging from near-Newtonian to “beads-on-a-string”. The inkjet printing behaviour does not correlate simply with the measured extensional relaxation times or Zimm times, but may be consistent with non-linear extensibility L and the production of fully extended polymer molecules in the thinning jet ligament. Fluid test methods allowing a more complete characterisation of NLVE parameters are needed to assess inkjet printing feasibility prior to directly jetting complex fluids. At the present time, directly jetting such fluids may prove to be the only alternative.

The fundamental scientific principle behind inkjet technology is the breakup of fluid jets or ligaments under surface tension, which involves the growth of infinitesimal perturbations along the free surface of the jet. Thus, in any computational model, it is imperative that the free surface is resolved accurately throughout the duration of the simulation. This chapter focuses on simulating the generation of jets and drops, and the dynamics of breakup behaviour. Three types of modelling are discussed in the chapter, namely, one‐dimensional modelling, axisymmetric modelling, and three‐dimensional simulation. The major requirements for most inkjet simulations include the following: accurate representation of jet breakup on small scales; accurate capture of the free surface dynamics of jets and thin ligaments; adaptive resolution in space and time; capacity to model the print‐head geometry; and capacity to include non‐Newtonian fluid models.