Effects of fluid film properties on fouling in biphasic flow systems

Abstract

Flow chemistry has the potential to enhance the large-scale accessibility of precision-engineered nanomaterials. While reactor fouling presented a major challenge in precision control, the liquid–liquid segmented flow method has been demonstrated to reduce or even eliminate it. However, guidelines for properly selecting materials and designing parameters in such systems are currently lacking. For these reasons, the present study investigated two biphasic flow systems for continuous gold nanoparticle (AuNP) synthesis. Visual observations showed no evidence of fouling in the silicone oil–water flow system, but some localized fouling was observed in the heptane-water flow system. The results indicated the silicone oil–water system gave a 50% lower polydispersity index and a 25% higher reaction yield due to fouling mitigation. We investigated two important factors of the continuous phase for fouling reduction: liquid film continuity and film thickness. Film continuity was evaluated by temperature-controlled contact angle measurements and the film dewetting velocity; And film thickness was estimated using two different mathematical models. It was concluded that the formation of a continuous oil film of thickness higher than the maximum surface asperities, as was the case only for the silicone oil–water flow system, is critical to eliminate fouling in continuous AuNP synthesis.