Visible light guided manipulation of liquid wettability on photoresponsive surfaces

Gibum Kwon,Seyed Reza Mahmoudi,Divya Panchanathan,Kripa K Varanasi,Gareth H Mckinley,Mohammed A Gondal

doi:10.1038/ncomms14968

Abstract

Photoresponsive titania surfaces are of great interest due to their unique wettability change upon ultraviolet light illumination. However, their applications are often limited either by the inability to respond to visible light or the need for special treatment to recover the original wettability. Sensitizing TiO2 surfaces with visible light-absorbing materials has been utilized in photovoltaic applications. Here we demonstrate that a dye-sensitized TiO2 surface can selectively change the wettability towards contacting liquids upon visible light illumination due to a photo-induced voltage across the liquid and the underlying surface. The photo-induced wettability change of our surfaces enables external manipulation of liquid droplet motion upon illumination. We show demulsification of surfactant-stabilized brine-in-oil emulsions via coalescence of brine droplets on our dye-sensitized TiO2 surface upon visible light illumination. We anticipate that our surfaces will have a wide range of applications including microfluidic devices with customizable wettability, solar-driven oil–water clean-up and demulsification technologies.

Highlights

Photoresponsive titania surfaces are of great interest due to their unique wettability change upon ultraviolet light illumination
A great deal of work has been devoted to elucidating the origin of the well-documented unique ultraviolet light-induced wettability change on TiO2 surfaces[2,11,12,13]
We demonstrate that a dye-sensitized TiO2 surface—fabricated using straightforward dip-coating method— can be engineered to have its wettability state optically modulated upon illumination by visible light

Summary

Introduction

Photoresponsive titania surfaces are of great interest due to their unique wettability change upon ultraviolet light illumination. To study the photo-induced wettability change of our N3 dyesensitized TiO2 surface, we measured the evolution in the contact angles in situ for three liquid droplets: deionized (DI) water, potassium iodide (KI, 10 wt% in water) and potassium chloride (KCl, 10 wt% in water).

Results

Conclusion