Microfluidic system manufacturing by direct laser writing for the generation and characterization of microdroplets

Abstract

Abstract This work contributes to the development of microfluidics devices in a simpler way and by keeping the cost of microfabrication as low as possible. Implementing methods to develop microfluidic devices and to have control over the channel size rapidly and easily have become a challenge. In the present work, direct laser writing (DLW) is proposed as a manufacturing technique to develop a T-junction microfluidic droplet generator operating in the squeezing regime. Owing to the channel size, DLW depends on both the focused laser spot properties and the interface material refractive indices. The Debye–Wolf theory behind this technique predicts the focal shift of the laser spot to avoid optical misalignment during the fabrication process. The Debye–Wolf theory and the COMSOL ray-tracing module are presented as complementary design tools. The flow rates and the channel sizes were investigated under the two-phase COMSOL module. Experimental droplet generation results were assisted with the solution of the Navier–Stokes equation with appropriate boundary conditions. Microdroplet size characterization, as well as simulations, show a linear tendency with the flow rate ratios (FRRs). For FRR ranging from 0.25 to 2, droplet lengths from ∼ 320   μ m to ∼ 1050   μ m were observed. This information is confirmed by implementing a digital image processing protocol. The dynamics of droplets formation, strongly influenced by the input flow rate fluctuations caused by the syringes and micropump operation, are presented. This protocol aims the full control of these devices to perform potential applications, such as particle insulators, drug delivery, fluidic microlasers, among others.