Microfluidics control the ballistic energy of thermocavitation liquid jets for needle-free injections

Illuminating a water solution with a focused continuous wave laser produces a strong local heating of the liquid that leads to the nucleation of bubbles, also known as thermocavitation. During the growth of the bubble, the surrounding liquid is expelled from the constraining microfluidic channel through a nozzle, creating a jet. The characteristics of the resulting liquid jet were imaged using ultra-fast imaging techniques. Here, we provide a phenomenological description of the jet shapes and velocities and compare them with a boundary integral numerical model. We define the parameter regime, varying jet speed, taper geometry, and liquid volume for optimal printing, injection, and spray applications. These results are important for the design of energy-efficient needle-free jet injectors based on microfluidic thermocavitation.