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Issue 15, 2019
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Directed motion of water droplets on multi-gradient photopolymer surfaces

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Abstract

The present work highlights the controlled directional movement of water droplets across a photopolymer surface. The movement is propelled by multi-gradients including a wettability gradient and a Laplace pressure gradient. Both gradients are conveniently adjusted by light employing a photoresponsive thiol–yne photopolymer. o-Nitrobenzyl alcohol derivatives with terminal alkyne groups are synthetized and cured across di- and tri-functional thiols upon visible light exposure. The wettability gradient is generated in a subsequent step involving an asymmetrical irradiation of the polymer surface with light in the UV-A spectral region. Polar groups are formed in the exposed areas due to the photocleavage of the chromophore and photo-oxidation reactions (upon prolonged UV exposure in air). The wettability rises with increasing exposure dose and gradient surfaces are prepared with static water contact angles ranging from 97 to 19°. By simultaneously inscribing the wettability gradient in wedge-shaped patterns, a Laplace pressure gradient is realized on the photopolymer surface, which can be easily tailored by the size and the angle of the wedge. The combination of both gradients enables a rapid and directed movement of water droplets (2 μL droplet) over a reasonable distance (up to 10 mm). Due to the high adhesion of the photopolymer surface, the droplet can be driven in a controlled way, even if the surface is inclined (20°) or turned upside down.

Graphical abstract: Directed motion of water droplets on multi-gradient photopolymer surfaces

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Article information


Submitted
25 Jan 2019
Accepted
08 Mar 2019
First published
12 Mar 2019

Polym. Chem., 2019,10, 1882-1893
Article type
Paper

Directed motion of water droplets on multi-gradient photopolymer surfaces

E. Rossegger, D. Hennen, T. Griesser, I. Roppolo and S. Schlögl, Polym. Chem., 2019, 10, 1882
DOI: 10.1039/C9PY00123A

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