(371j) The Effects of Viscosity and Surfactant Concentration On Two Phase Flow in a T-Junction Microfluidic Device

An initial study on the relationship between hydrophilic surfactant concentration, flow ratio, and the dynamic contact angle of a water plug in a water-in-oil (W/O) emulsion was conducted to determine the influence of the oil phase viscosity and the hydrophilic surfactant concentration on both the flow and emulsion types in a T-junction microfluidic device. Cetyltrimethyl ammonium bromide (CTAB) was used as the hydrophilic surfactant in a water-corn oil emulsion, and the surfactant concentration ranged from 1 x 10-2 ? 3 x 10-2 % (w/w) to focus on a region in which the interplay between viscous and interfacial forces in a microchannel could be emphasized. Two phase flow rate ratios ranged from 1:10 to 10:1. The high viscosity of the oil phase (67 mPa-s) yielded aqueous plugs with lengths ranging from greater than 2.5 mm to less than 0.5 mm. Still photos of the plugs were taken with a high speed CCD camera and dynamic contact angles were determined with the aid of DataPhysics contact angle software. The dynamic contact angles of the aqueous plugs ranged from near complete spreading at ~5° to hydrophobic interaction at angles greater than 110°. The results indicate that, for a specific surfactant concentration range, both the continuous phase viscosity and the flow ratio play important roles in determining the dynamic contact angle and distortion of dispersed phase plugs in a microchannel. Furthermore, continued research in this area can clarify the energetics involved in creating and controlling both O/W and W/O emulsions and phase inversions.

Key words: Microfluidic Device; Dynamic contact angle; Two phase flow

Correspondence: Dr. J.H. Xu (xujianhong@tsinghua.edu.cn); Prof. Dr. G.S. Luo (gsluo@tsinghua.edu.cn).