[Vacuum] Photoresponsive hierarchical ZnO-PDMS surfaces with azobenzene-polydopamine coated nanopart
Azobenzene-bearing surfaces are promising for light-controlled wettability switching in microfluidic systems. We investigate the wettability and stability of flat glass, flat polydimethylsiloxane (PDMS) and hierarchical ZnO-PDMS surfaces functionalized with azobenzene bearing polydopamine coated nanoparticles (Azo-PDA-NP). We analyse the stability of the contact-angle switching when using new droplet locations for each measurement and for using the same droplet location with compressed-nitrogen drying between measurements. For flat glass surfaces we observed a wettability change of 15° and 60° for spin-coating and drop-casting deposition of the Azo-PDA-NP, respectively. For the PDMS samples, 60° contact-angle change are obtained, but these surfaces show degradation for repeated switching cycles. In contrast the hierarchical ZnO-PDMS surfaces exhibit a wettability switch of 50° and no degradation for five switching cycles at the same droplet location. We captured water drops during ultra-violet (UV) irradiation on video and obtained a one-sided flowing motion with a speed of 1.9 μm/s. Contact-angle hysteresis measurements show that the minimum criterion for droplet movement is fulfilled for the Azo-PDA-NP functionalized hierarchical ZnO-PDMS surfaces.
Christine Kallweita, , , Matthias Bremera, Daria Smaznab, Torben Karrocka, Rainer Adelungb, Martina Gerkena a Chair of Integrated Systems and Photonics, Institute of Electrical Engineering and Information Technology, Kiel University, Kaiserstrasse 2, 24143 Kiel, Germany b Chair of Functional Nanomaterials, Institute for Materials Science, Kiel University, Kaiserstrasse 2, 24143 Kiel, Germany Received 9 December 2016, Revised 23 February 2017, Accepted 3 March 2017, Available online 19 March 2017 http://dx.doi.org/10.1016/j.vacuum.2017.03.023