Capabilities and Limitations of Fire-Shaping to Produce Glass Nozzles

Alejandro Rubio,Maria G. Cabezas,Sergio Rodríguez

doi:10.3390/ma13235477

Abstract

Microfluidic devices for drop and emulsion production are often built using fire-shaped (or fire-polished) glass nozzles. These are usually fabricated manually with inexpensive equipment. The shape limitations and poor reproducibility are pointed as the main drawbacks. Here, we evaluate the capabilities of a new fire-shaping approach which fabricates the nozzle by heating a vertical rotating capillary at the Bottom of a Lateral Flame (BLF). We analyze the effect of the heating conditions, and the capillary size and tolerances. The shape reproducibility is excellent for nozzles of the same size produced with the same conditions. However, the size reproducibility is limited and does not seem to be significantly affected by the heating conditions. Specifically, the minimum neck diameter standard deviation is 3%. Different shapes can be obtained by changing the heating position or the capillary dimensions, though, for a given diameter reduction, there is a minimum nozzle length due to the overturning of the surface. The use of thinner (wall or inner diameter) capillaries allows producing much shorter nozzles but hinders the size reproducibility. Finally, we showed an example of how the performance of a microfluidic device is affected by the nozzle shape: a Gas Dynamic Virtual Nozzle (GDVN) built with a higher convergent rate nozzle works over a wider parametric range without whipping.

Highlights

Microfluidics is receiving growing attention in numerous fields, especially in biotechnology where it is becoming a key tool
Though the fire-shaping idea is simple, the phenomena involved in the process are not
Fire-shaped nozzles are commonly used in microfluidic device assemblies

Summary

Introduction

Microfluidics is receiving growing attention in numerous fields, especially in biotechnology where it is becoming a key tool. Research in microfluidics involves both the understanding of the physics of flows at such small scales and the development of the devices for different applications. Three-dimensional devices can be built by the assembly of glass capillaries [2,3,4]. The advantages of glass are that it is chemically robust, and has good mechanical and optical properties. It allows building very versatile devices, their fabrication has a few drawbacks. Different 3D printing techniques have been proposed for fabricating microfluidic devices, most with millimetric scale features. The resolution improvement of some techniques is broadening their applicability for building real microfluidic devices [5]

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Conclusion