(186a) Multi-Phase Flow in Co-Axial Microfluidic Devices for Controllable Preparation of Microscale Materials

The controlled preparation of microscale functional materials in microfluidic devices has been the focus of numerous studies in the last few years. In this work, we focus on the fundamental of multi-phase flow in co-axial microfluidic devices and its applications for controllable preparation of microscale materials. Firstly, the two-phase flow patterns and droplet formation mechanisms for the liquid-liquid systems were studied in co-axial microfluidic devices. Different factors including the microchannel structure, the system physical properties, and the flow rates were investigated. The flow patterns could be divided into ?dripping flow', ?jetting flow' and ?laminar flow' by changing the two phase flow ratio. Two mathematical models for the prediction of droplet size were developed in the dripping and jetting flow separately. Futhermore, tri-phase flow in double co-axial microdevices were studied and double emulsions or tri-phase co-laminar flow could be controllable prepared by choosing different working systems and operation conditions. Based on the droplet formation in microfluidic devices, experiments on the solidification of monodispersed droplets (double emulsions) were conducted. Different solification methods including solvent extraction, solvent evaporation, crosslinking and UV-polymerization were used to preparation monodispersed calcium alginate, chitosan and PSt microparticles. The size and structure of the microparticles can be controlled. Based on the tri-phase co-laminar flow, experiments on the preparation of uniform tubes were conducted. Three kinds of polymeric solutions were selected as the middle phase while a polyethyleneglycol aqueous solution was used as the inner and outer phases in the microfluidic process. Highly uniform tubes were successfully fabricated by the solvent extraction method. Both the outer diameter of the tubes and the wall thickness could be adjusted by varying the flux of the fluids and the rolling velocity of the collection roller. The results will be very helpful for the development of novel technology and equipments for the preparation of monodispersed microscale materials, such as functional microspheres, microcapsules, hollow fiber membranes, and so on.

Key words: multi-phase flow; microfluidic; microparticle; microscale tube

Acknowledgement We acknowledge the financial supports of the National Natural Science Foundation of China (No. 20806042, 20876084) and and SRFDP(20090002110070) on this work gratefully.