Regimes of polymer behaviour in drop-on-demand ink-jetting

摘要: A recent model for the drop-on-demand (DoD) jetting of mono-disperse linear polymer solutions has identified three regimes behaviour: with chains fully relaxed; significant viscoelastic effects; and extended. These have now been confirmed by experimental observations in several different systems. The predicts maximum jettable concentration as a function molecular weight. highly extensional flows high-speed viscous solvents can stretch outside nozzle, permitting higher contents than purely elastic behaviour. results are DoD printing at high jet speeds will be relevant to formation from any printhead. Introduction Drop-on-demand ink-jet dilute solutions, fixed drive waveform achieve main drop tip speed ~ 6 m/s 1 mm standoff had studied highresolution spark flash imaging [1]. Dilute polystyrene (PS) near weights (Mw) 24,000 488,000 g/mol were prepared good but solvent, diethyl phthalate (DEP). dependence on length (L) PS was determined. Zimm-Rouse theory polymers solution provides quantitative relation between L Mw described elsewhere [2]. low dilutions expected show behaviour either controlled viscosity tending towards Newtonian solvent lowest concentrations, or “elastic” behaviour, falling rapidly (at least an inverse square law) Mw. However both our experiments [3, 4] numerical simulations [5] appeared variation this limiting close 1/Mw, which unexplained theory. Earlier results, de Gans et al [6], slower (~ 2 m/s) jets another “good” print head type We sought understand these apparent discrepancies. Numerical & models code developed Morrison Harlen validated separately CIJ conditions, using large-scale generator system [7] well various scale industrial inkjet [8]. This axi-symmetric fluid flow incorporates Zimm shear rate predicted relationship required unexpected consistent data DEP obtained earlier work. Recently [9], possible regime considered: if become stretched, i.e. beyond region, how does affect jetting? Once stretched they behave like rigid rods solution, very >100 times extension rate. (The ratio [9] is given 2⁄3L2, > 100,000 value ~15.) suggests power-law that still not conform directly all measurements, since it neglects key aspects ink-jets. previous approach understanding inkjets [10] based simple extending ligament combined gave descriptions conditions under initially ejected nozzle never separates, retracts back inside (“bungee jumpers”). However, applied only relatively rates (jet speeds) compared those reported here. Figure shows ink-jet. 1: Basic following [10]. Using multi-mode model, found fast combination thinning during reduced overall observed ink-jets (viscous) (DEP), also providing some explanations scaling law simulation [5]. Model Three [9]: two well-known third previously clearly literature data. Transitions depend initial Weissenberg number (Wi) product (ė) relaxation time (τ), where we approximate (U0) (d) neck (see 1):