Stretching and entrainment in jet-assisted wet spinning (JAWS)

A submerged fluid jet can entrain and accelerate surrounding fluid to a speed comparable to the jet velocity. Recently, we have used a submerged liquid jet in jet-assisted wet spinning (JAWS) to stretch a nearby pre-fiber (liquid) jet to make hydrogel fibers thinner than the diameter of the spinneret. In this work, we systematically investigated the diameter of the pre-fiber jet as a function of its flow rate and placement distance to the main submerged liquid jet. We find that the pre-fiber jet diameter scales as the square root of its flow rate when the flow rate ratio between the pre-fiber jet and main jet is small, hinting (because of mass conservation) at constant pre-fiber jet velocity after being entrained by the main jet. Deviation from the square root scaling at high pre-fiber jet flow rates is found to be related to the high flow rate ratio between the pre-fiber jet and main jet that delays entrainment by the main jet. A model based on the Landau-Squire solution to describe the main jet is used to model the different entrainment behaviors.