Phase diagram of pinch-off behaviors during drop-ondemand inkjetting of alginate solutions

Viscoelastic polymer solutions have been extensivelyutilized in drop-wise manufacturing (such as inkjetprinting) for a variety of biomedical applications. Thepinch-off of viscoelastic jets is a key step towardsgeneration of droplets in inkjet printing. This complexprocess is governed by interplay of four stresses includinginertial stress, capillary stress, viscous stress, and elasticstress. Depending on polymer solution properties andprocess conditions, four types of pinch-off phenomenonwere observed during inkjetting of viscoelastic alginatesolutions. In this study, material properties of alginatesolutions with different concentrations have beencharacterized, and three dimensionless numbers(Ohnesorge number Oh, Deborah number De and Webernumber We) have been proposed to analyze differentpinch-off behaviors. Phase diagram in terms of these threedimensionless numbers has been constructed to classify theregimes for different pinch-off types during inkjetting ofviscoelastic alginate solutions. It is found that: 1) At lowDe and Oh, the viscoelastic effect is small. The capillarystress is mainly balanced by the inertial stress, resulting infront pinching. 2) At medium De and low Oh, the capillarystress is still mainly balanced by the inertial stress, but theelastic effect starts to show its effect by delaying theligament thinning near the front-pinching location. Withthe increase of We, the pinch-off type may change fromfront pinching to hybrid pinching to exit pinching. 3) Atlow Oh and high De, the viscous and inertial effects aresmall. The capillary stress is mainly balanced by the elasticstress, resulting in exit pinching. 4) At high Oh and De, theviscoelastic effect is dominant. The capillary stress ismainly balanced by the viscous and elastic stresses. Withthe increase of We, middle pinching turns to be exitpinching due to the increase of the initial ligament diameternear the forming droplet.