Letter | Published:

Dynamically reconfigurable complex emulsions via tunable interfacial tensions

Nature volume 518, pages 520524 (26 February 2015) | Download Citation

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Abstract

Emulsification is a powerful, well-known technique for mixing and dispersing immiscible components within a continuous liquid phase. Consequently, emulsions are central components of medicine, food and performance materials. Complex emulsions, including Janus droplets (that is, droplets with faces of differing chemistries) and multiple emulsions, are of increasing importance1 in pharmaceuticals and medical diagnostics2, in the fabrication of microparticles and capsules3,4,5 for food6, in chemical separations7, in cosmetics8, and in dynamic optics9. Because complex emulsion properties and functions are related to the droplet geometry and composition, the development of rapid, simple fabrication approaches allowing precise control over the droplets’ physical and chemical characteristics is critical. Significant advances in the fabrication of complex emulsions have been made using a number of procedures, ranging from large-scale, less precise techniques that give compositional heterogeneity using high-shear mixers and membranes10, to small-volume but more precise microfluidic methods11,12. However, such approaches have yet to create droplet morphologies that can be controllably altered after emulsification. Reconfigurable complex liquids potentially have great utility as dynamically tunable materials. Here we describe an approach to the one-step fabrication of three- and four-phase complex emulsions with highly controllable and reconfigurable morphologies. The fabrication makes use of the temperature-sensitive miscibility of hydrocarbon, silicone and fluorocarbon liquids, and is applied to both the microfluidic and the scalable batch production of complex droplets. We demonstrate that droplet geometries can be alternated between encapsulated and Janus configurations by varying the interfacial tensions using hydrocarbon and fluorinated surfactants including stimuli-responsive and cleavable surfactants. This yields a generalizable strategy for the fabrication of multiphase emulsions with controllably reconfigurable morphologies and the potential to create a wide range of responsive materials.

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Acknowledgements

Financial support from Eni S.p.A. under the Eni-MIT Alliance Solar Frontiers Program and by the US Army Research Laboratory and the US Army Research Office through the Institute for Soldier Nanotechnologies under contract number W911NF-13-D-0001 is acknowledged. E.M.S. and J.A.K. were supported by F32 Ruth L. Kirschtein NRSA Fellowships under award numbers EB014682 (E.M.S.) and GM106550 (J.A.K.). We thank L. Arriaga for introducing us to the fabrication of capillary microfluidic devices.

Author information

Affiliations

  1. Department of Chemistry and Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Lauren D. Zarzar
    • , Ellen M. Sletten
    • , Julia A. Kalow
    •  & Timothy M. Swager
  2. Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Vishnu Sresht
    •  & Daniel Blankschtein

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Contributions

L.D.Z. and T.M.S. developed the concept for the research. L.D.Z. conducted experiments involving emulsion fabrication and imaging, and measured interfacial tensions. V.S. and D.B. modelled the system and calculated and analysed equilibrium interfacial tensions. E.M.S. synthesized the fluorinated crosslinker and fluorinated coumarin dye. J.A.K. synthesized the light-responsive surfactant and the cleavable surfactant. All authors contributed to the writing of the manuscript.

Competing interests

The authors have filed two patent applications based on the research presented in this paper.

Corresponding authors

Correspondence to Daniel Blankschtein or Timothy M. Swager.

Extended data

Supplementary information

Videos

  1. 1.

    A drop of 10% Zonyl fluorosurfactant is added to a solution of 0.1% SDS-stabilized perfluorohexane/hexane/water double emulsions.

    As Zonyl diffuses and creates a concentration gradient, we observe that the droplet morphology dynamically changes by first passing through a spherical Janus droplet conformation before inverting to a hexane/perfluorohexane/water double emulsion. The hexane phase is dyed red. The video is in real time.

  2. 2.

    A drop of 5% SDS is added to a solution of 0.1% Zonyl-stabilized hexane/perfluorohexane/water double emulsions.

    As SDS diffuses and creates a concentration gradient, we observe that the droplet morphology dynamically changes by first passing through a spherical Janus droplet conformation before inverting to a perfluorohexane/hexane/water double emulsion. The hexane phase is dyed red. The video is in real time.

  3. 3.

    Droplets undergo a reversible transition from a hexane/perfluorohexane/water double emulsion to a Janus conformation in response to UV and blue light.

    The transition is achieved by utilizing a combination of Zonyl fluorosurfactant and a light-responsive azobenzene surfactant. Most droplets are oriented with the denser perfluorohexane phase downward and are viewed from above, but a few droplets are pinned to the substrate and the transition is viewed from the side. The hexane phase is dyed red. The solution’s yellow tint results from the azobenzene surfactant used. The video is in real time.

  4. 4.

    A droplet undergoes a reversible transition between perfluorohexane/hexane/water double emulsion and hexane/perfluorohexane/water double emulsion configurations.

    The transition is achieved by utilizing a combination of Zonyl fluorosurfactant and a light-responsive azobenzene surfactant. The hexane phase is dyed red. The solution’s yellow tint results from the azobenzene surfactant used. The video is in real time.

About this article

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DOI

https://doi.org/10.1038/nature14168

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