Projection micro-stereolithography versus master–slave approach to manufacture a micro-optofluidic device for slug flow detection

In this work, the use of projection micro-stereolithography (PμSL) to 3D print a micro-optofluidic device for slug flow detection is presented. For comparison purposes, a poly-dimethylsiloxane (PDMS)–based device was also manufactured by a novel master–slave 3D printing approach. The micro-optofluidic device has a microfluidic T-junction with a micro-optical section that consists of two optical fiber insertions used for slug flow detection. The design of the device also includes two micro-channels for the optical fiber’s insertion, needed to acquire a light signal, which give a direct information about the microfluidic channel inner flow by exploiting the absorption phenomenon. The working principle in the detection is based on a different light transmission correlated to the fluid interfering with the laser beam in a micro-channel section. The two materials used for the two manufacturing approaches were fully characterized in terms of their surface properties via both Atomic Force Microscopy (AFM) and angle of contact measure. The process within the two micro-channels was monitored optically and a signal correlated to the slug passage was analyzed for the flow tracking. A wide experimental campaign was done for the device manufactured through the PμSL technique in different operative conditions. Thus, the optimal one was identified through the Analysis of Variance (ANOVA). Then, a detailed comparison between the slug process detected inside the HTL resin device and the PDMS device was carried out to evaluate the pros and cons of using different materials and fabrication techniques. The analysis run on the two devices revealed that the HTL resin device can be used for slug flow detection, but future research is still needed to obtain a resin allowing to outperform the PDMS device.