報告人：Prof. Robin H. A. Ras
題 目：The challenge of accurate characterization of surface wetting
Wetting is typically characterized from a sessile droplet by evaluating the angle at the contact line where liquid, air and solid meet. Contact angle goniometry is considered as the gold standard of wetting characterization, however, is prone to inaccuracies, especially towards high contact angles.[2-5]
In this talk, I will describe the problem and present state-of-the-art methodologies for evaluating wetting of hydrophobic surfaces with enhanced accuracy. Oscillations of magnetic water droplets allow measurement of friction forces between droplet and surface with nanonewton sensitivity. Adhesion forces between droplet and surface can be measured by scanning droplet adhesion microscopy with sensitivity down to nanonewton (Figure 1).
Figure 1. Scanning droplet adhesion microscopy allows to obtain wetting maps, a new concept for hydrophobic surface characterization, visualizing wettability variations with micronscale spatial resolution.
 Huhtam?ki T., Tian X., Korhonen J.T., Ras R.H.A. Nature Protocols 13, 1521 (2018).
 Butt H.-J., Roisman I.V., Brinkmann M., Papadopoulos P., Vollmer D., Semprebon C., Curr. Opin. Colloid Interface Sci. 19, 343 (2014).
 Tian X., Verho T., Ras R.H.A., Science 352, 142 (2016).
 Liu K., Vuckovac M., Latikka M., Huhtam?ki T., Ras R.H.A., Science 363, 1147 (2019).
 Vuckovac M., Latikka M., Liu K., Huhtam?ki T., Ras R.H.A., Soft Matter 15, 7089 (2019).
 Timonen J.V.I., Latikka M., Ikkala O., Ras R.H.A., Nature Communications 4, 2398 (2013).
 Liimatainen V., Vuckovac M., Jokinen V., Sariola V., Hokkanen M., Zhou Q., Ras R.H.A., Nature Communications 8, 1978 (2017).
Robin Ras is head of the Soft Matter and Wetting research group at Department of Applied Physics, Aalto University (Finland). His research area is situated at the interface between physics, chemistry and materials science, dealing with fundamental scientific problems and technological applications. He has authored over 120 scientific publications, including several in journals from the Science and Nature family. In 2016, Robin Ras received the ERC Consolidator grant for research on extremely water-repellent surfaces. He received the Anton Paar Research Award for Instrumental Analytics & Characterization (2018) for the invention Scanning Droplet Adhesion Microscopy.