Research into Multi-scale Examination of MultiPHase physIcs in flowS (MEMPHIS)

Posted by Kyeong Hyeon Park | March - 1 - 2017 | 0 Comment

Many industrial products, i.e. milk, paint and shampoo, are emulsion-based systems and require drops of a preferred size. Microfluidic devices, such as flow-focusing channels, can provide narrow drop size distributions. In many cases surfactants are used to stabilise the emulsions, which  add complexity to the drop formation process.

At UCL we investigate the hydrodynamic characteristics and velocity profiles of aqueous drops in a flow-focusing device with and without surfactants present. This study is part of a collaborative work with the University of Birmingham, within the MEMPHIS framework.

Silicone oil (μ = 0.0046 Pa s, Sigma-Aldrich) was used as a continuous phase whereas 52% water/48 % glycerol mixture (w/w) was used as the dispersed one. One of two ionic surfactants, dodecyltrimethylammonium bromide (C12TAB), hexadecyltrimethylammonium bromide (C16TAB) (Sigma) was dissolved in the aqueous phase. All runs were carried out in a glass microchannel with hydraulic diameter 290 μm at for a variety of flowrates.

The various stages of drop formation shown in Fig. 1a were studied using the two-colour Particle Image Velocimetry technique[1]. The velocity field in the aqueous phase at stage 2 is shown in Fig. 1b:

Evita_Nina

Fig. 1: (a) Typical micro-PIV images of aqueous phase during drop formation (b) Averaged V component of the velocity field of the surfactant-free system (Qaq = 0.01 cm3/min and Qoil = 0.003 cm3/min).

[1] Chinaud M, Roumpea E, Angeli P. Studies of plug formation in microchannel liquid–liquid flows using advanced particle image velocimetry techniques. Experimental Thermal and Fluid Science. 2015;69:99–110.

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