Effect of viscosities of dispersed and continuous phases in microchannel oil-in-water emulsification

Abstract

Although many aspects of microchannel emulsification have been covered in literature, one major uncharted area is the effect of viscosity of both phases on droplet size in the stable droplet generation regime. It is expected that for droplet formation to take place, the inflow of the continuous phase should be sufficiently fast compared to the outflow of the liquid that is forming the droplet. The ratio of the viscosities was therefore varied by using a range of continuous and dispersed phases, both experimentally and computationally. At high viscosity ratio (g d /g c ), the droplet size is constant; the inflow of the continuous phase is fast compared to the outflow of the dispersed phase. At lower ratios, the droplet diameter increases, until a viscosity ratio is reached at which droplet formation is no longer possible (the minimal ratio). This was confirmed and elucidated through CFD simulations. The limiting value is shown to be a function of the microchannel design, and this should be adapted to the viscosity of the two fluids that need to be emulsified.

Temperature effect on microchannel oil-in-water emulsification

“…4a) is an important parameter in determining droplet size (Kawakatsu et al 2001). Our previous study using the MC array (MS104) demonstrated that droplet size was not influenced by the viscosity ratio above a critical value of 4 (van Dijke et al 2010). The viscosity of both phases was varied in this case.…”

“…The viscosity ratio, defined as the ratio of the viscosity of the dispersed phase to the viscosity of the continuous phase, also decreased exponentially by 2.7 times as temperature increased. The viscosity ratio values were in the range of 28-77 at T C of 10-70°C, which range is above 4 the critical viscosity ratio determined by van Dijke et al 2010, where droplet size is not influenced by viscosity ratio. The interfacial tension for the two-phase system containing SDS increased by 2.0 times as T C increased from 10 to 70°C.…”

“…The surface creation rate (j) during detachment can be approximated by the following equation (van Dijke et al 2010):…”

Production of uniform droplets using membrane, microchannel and microfluidic emulsification devices

“…Symmetric MCs are of the same size and shape (e.g., circular or rectangular) along the whole cross section of the plate. Rectangular MCs provide better performance in MCE than circular MCs and an aspect ratio of slot length to slot width should be at least 3−3.5 to ensure production of uniform droplets (Kobayashi et al 2004(Kobayashi et al , 2009avan Dijke et al, 2010c).…”

A comparative study on particle–fluid interactions in micro and nanofluids of aluminium oxide

“…But long term stability of the nanofluids could be a practical issue. Long term stability of nanoparticle suspensions is critical to fully appreciate the benefits of nanofluids (Das et al 2008).…”