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O: Fachverband Oberflächenphysik

O 102: Focus Session: Wetting on Adaptive Substrates III (joint session CPP/DY/O)

O 102.4: Vortrag

Freitag, 22. März 2024, 10:30–10:45, H 0110

Electro(de)wetting with Photoswitches: Control of wetting by electric fields and light — •Billura Shakhayeva and Björn Braunschweig — University of Münster, Institute of Physical Chemistry, 48149 Münster, Germany

Electro-dewetting (EDeW) was introduced as a new method in order to change the wetting properties of surfaces. The underlying mechanism is, however, not fully understood and additional experiments are needed. For that, we have replaced the DTAB surfactants used in the original work [1] by arylazopyrazole triethylammonium bromide (AAP-TB) which is a cationic surfactant that can change the surface tension at the air-water interface to a large extend through E/Z photoisomerization [2]. This offers to fine tune the contact angle during EDeW by E/Z photoisomerization of AAP-TB and we find a further increase in contact angle by ∼ 6^∘ when the samples were irradiated by UV light that triggers photoisomerization from the E to the less surface-active Z isomer. Li et al.[1] suggested that surfactants are deposited on the silicon oxide surface through the EDeW process. In order to study the possible deposition of surfactants and the role of a possible prewetting layer outside of the drop and at some distance from the 3-phase contact line we have done sum-frequency generation (SFG) spectroscopy and find that surfactants are deposited even several mm adjacent to the drop and that their structure as well as the structure of the accompanying water layer changes drastically close to the 3-phase contact line. [1] Li et al. Nature, 572, 507-510 (2019) [2] Schnurbus et al. J. Phys. Chem. B 124, 6913 (2020).

Keywords: Electro-dewetting; Photoswitchables