In-Channel Responsive Surface Wettability for Reversible and Multiform Emulsion Droplet Preparation and Applications

Lanhui Li, Zhibin Yan, Mingliang Jin, Xiangshen You, Shuting Xie, Zhenping Liu, Albert van den Berg, Jan C.T. Eijkel, Lingling Shui*

*Corresponding author for this work

    Research output: Contribution to journalArticleAcademicpeer-review

    36 Citations (Scopus)
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    We report on a simple approach for in-channel functionalization of a polydimethylsiloxane (PDMS) surface to obtain a switchable and reversible wettability change between hydrophilic and hydrophobic states. The thermally responsive polymer, poly(N-Isopropylacrylamide) (PNIPAAm), was grafted on the surface of PDMS channels by UV-induced surface grafting. PNIPAAm-grafted PDMS (PNIPAAm-g-PDMS) surface wettability can be thermally tuned to obtain water contact angles varying in the range of 24.3 to 106.1° by varying temperature at 25-38 °C. By selectively modifying the functionalized area in the microfluidic channels, multiform emulsion droplets of oil-in-water (O/W), water-in-oil (W/O), oil-in-water-in-oil (O/W/O), and water-in-oil-in-water (W/O/W) could be created on-demand. Combining solid surface wettability and liquid-liquid interfacial properties, tunable generation of O/W and W/O droplet and stratified flows were enabled in the same microfluidic device with either different or the same two-phase fluidic systems, by properly heating/cooling thermal-responsive microfluidic channels and choosing suitable surfactants. Controllable creation of O/W/O and W/O/W droplets was also achieved in the same microfluidic device, by locally heating or cooling the droplet generation areas with integrated electric heaters to achieve opposite surface wettability. Hollow microcapsules were prepared using double emulsion droplets as templates in the microfluidic device with sequential hydrophobic and hydrophilic channel segments, demonstrating the strength of the proposed approach in practical applications.

    Original languageEnglish
    Pages (from-to)16934-16943
    Number of pages10
    JournalACS Applied Materials and Interfaces
    Issue number18
    Publication statusPublished - 8 May 2019


    • Droplet
    • Microcapsule
    • Microfluidics
    • Multi-emulsion
    • Reversible emulsion
    • Surface wettability
    • Thermoresponsive


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