Jetting behavior of polymer solutions in drop-on-demand inkjet printing

The jetting of dilute polymer solutions in drop-on-demand printing is investigated. A quantitative model is presented which predicts three different regimes of behavior depending upon the jet Weissenberg number Wi and extensibility of the polymer molecules. In regime I (Wi < 1/2), the polymer chains are relaxed and the fluid behaves in a Newtonian manner. In regime II (1/2 < Wi < L), where L is the extensibility of the polymer chain, the fluid is viscoelastic, but the chains do not reach their extensibility limit. In regime III (Wi > L), the chains remain fully extended in the thinning ligament. The maximum polymer concentration at which a jet of a certain speed can be formed scales with molecular weight to the power of (1-3 nu), (1-6 nu), and -2 nu in the three regimes, respectively, where nu is the solvent quality coefficient. Experimental data obtained with solutions of monodisperse polystyrene in diethyl phthalate with molecular weights between 24 and 488 kDa, previous numerical simulations of this system, and previously published data for this and another linear polymer in a variety of good solvents, all show good agreement with the scaling predictions of the model. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.4724331]