Abstract
Static contact angle hysteresis determines droplet stickiness on surfaces, and is widely attributed to surface roughness and chemical contamination. In the latter case, chemical defects create free-energy barriers that prevent the contact line motion. Electrowetting studies have demonstrated the similar ability of electric fields to alter the surface free-energy landscape. Yet, the increase of apparent static contact angle hysteresis by electric fields remains unseen. Here, we report the observation of electrowetting hysteresis on micro-striped electrodes. Unlike most experiments with stripes, the droplet spreading on the substrate is experimentally found to be isotropic, which allows deriving a simple theoretical model of the contact angle hysteresis depending the applied voltage. This electrowetting hysteresis enables the continuous and dynamic control of contact angle hysteresis, not only for fundamental studies but also to manufacture sticky-on-demand surfaces for sample collection.
Highlights
Static contact angle hysteresis determines droplet stickiness on surfaces, and is widely attributed to surface roughness and chemical contamination
In summary, we report the experimental control of static apparent contact angle hysteresis (CAH) by an inhomogeneous electric field, in formal analogy with chemical defects
Noting that the droplet spreads in an isotropic fashion, we derive a thermodynamic model to interpret these observations for small CAH
Summary
Experimental increase of the apparent CAH with electrical voltage. The experimental set-up[42], shown in Fig. 1a–c, is similar to the dielectrowetting chip used previously by McHale et al.[30]. For the sake of clarity, we only show 0 and 40 V, while varying the initial droplet volumes from 10 to 50 μL and the electrode pitch from 50 to 200 μm (comparison over a broader range of voltages is available in Fig. S7 in Supplementary Note 5). These experiments were carried out immediately after manufacturing the substrates, resulting in a very low CAH (3.1°) in.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
