Screening of the effect of surface energy of microchannels on microfluidic emulsification

Wei Li, Zhihong Nie, Hong Zhang, Chantal Paquet, Minseok Seo, Piotr Garstecki, Eugenia Kumacheva

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74 Scopus citations


We report the results of a systematic study of the effect of the surface energy of the walls of microchannels on emulsification in parallel flow-focusing microfluidic devices. We investigated the formation of water-in-oil (W/O) and oil-in-water (O/W) emulsions and found that the stability of microfluidic emulsification depends critically on the preferential wetting of the walls of the microfluidic device by the continuous phase. The condition for stable operation of the device is, however, different than that of complete wetting of the walls by the continuous phase at equilibrium. We found that W/O emulsions form when the advancing contact angle of water on the channel wall exceeds θ ≈ 92°. This result is unexpected because at equilibrium even for θ < 92° the microchannels would be completely wet by the organic phase. The criterion for the formation of W/O emulsions (θ > 92°) is thus more stringent than the equilibrium conditions. Conversely, we observed the stable formation of O/W emulsions for θ < 92°, that is, when the nonequilibrium transition to complete wetting by oil takes place. These results underlie the importance of pinning and the kinetic wetting effects in microfluidic emulsification. The results suggest that the use of parallel devices can facilitate fast screening of physicochemical conditions for emulsification.

Original languageEnglish
Pages (from-to)8010-8014
Number of pages5
Issue number15
StatePublished - Jul 17 2007


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