Abstract
Jet formation and break-up in inkjet printing has been studied and understood mainly for pure liquids. Questions remain as to the role of surfactants on the inkjet printing process at the microsecond timescale. Here, numerical and experimental results demonstrating the effects of surfactants on jet break-up and drop formation at the scales relevant to drop-on-demand inkjet printing are presented. The rapid expansion of the free surface during the fast jetting process results in a depletion of surfactants along the air–liquid interface, resulting in surface tension gradients. During ejection, surfactants are concentrated toward the head of the droplet, while the trailing ligament is found to be almost devoid of surfactants. As a consequence, the initial evolution and pinch-off of the jet from the nozzle are found to be very similar to that of pure water, even though the equilibrium surface tension of the surfactant solution is lower by a factor of two. However, particularly for strong surfactants, Marangoni forces arising from surface tension gradients between the head drop and the ligament are found to delay and can even prevent the break-up of the main drop from the ligament thereby inhibiting the formation of satellite drops.
Highlights
A surface active agent or surfactant is a molecule, which is characterized by its tendency to absorb at surfaces and interfaces
Numerical and experimental results demonstrating the effects of surfactants on jet break-up and drop formation at the scales relevant to drop-on-demand inkjet printing are presented
I.e., concentrations above the critical micelle concentration (CMC), surfactants aggregate into micelles in which the hydrophobic group is directed toward the interior of the cluster[2] thereby shielding the hydrophobic group from the water and so reducing the free energy of the system
Summary
A surface active agent or surfactant is a molecule, which is characterized by its tendency to absorb at surfaces and interfaces. I.e., concentrations above the critical micelle concentration (CMC), surfactants aggregate into micelles in which the hydrophobic group is directed toward the interior of the cluster[2] thereby shielding the hydrophobic group from the water and so reducing the free energy of the system. Surfactants are commonly used in product formulations. Their versatility makes them very useful in diverse products such as motor oils, pharmaceutical products, laundry detergents and other house cleaning products, drilling muds, and the flotation agents used in beneficiation of ores. The applications of surfactants have been extended to high-technology areas such as electronic printing, biotechnology, micro-electronics, and viral research.[11]
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