title: Sessile Nanodroplets on Elliptical Patches of Enhanced Lyophilicity.
abstract: We theoretically investigate the shape of a nanodroplet on a lyophilic elliptical patch in lyophobic surroundings on a flat substrate. To compute the droplet equilibrium shape, we minimize its interfacial free energy using both Surface Evolver and Monte Carlo calculations, finding good agreement between the two methods. We observe different droplet shapes, which are controlled by the droplet volume and the aspect ratio of the ellipse. In particular, we study the behavior of the nanodroplet contact angle along the three-phase contact line, explaining the different droplet shapes. Although the nanodroplet contact angle is constant and fixed by Young's law inside and outside the elliptical patch, its value varies along the rim of the elliptical patch. We find that because of the pinning of the nanodroplet contact line at the rim of the elliptical patch, which has a nonconstant curvature, there is a regime of aspect ratios of the elliptical patch in which the nanodroplet starts expanding to the lyophobic part of the substrate, although there is still a finite area of the lyophilic patch free to be wetted.
authors.affiliation: Physics of Fluids Group, Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Ivan
authors.identifier: 0000-0003-0977-9973
authors.initials: I
authors.lastname: Dević
authors.affiliation: Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University , Leuvenlaan 4, 3584 CE Utrecht, The Netherlands.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Soligno
authors.affiliation: Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University , Princetonplein 5, 3584 CC Utrecht, The Netherlands.
authors.forename: Marjolein
authors.initials: M
authors.lastname: Dijkstra
authors.affiliation: Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University , Leuvenlaan 4, 3584 CE Utrecht, The Netherlands.
authors.forename: René van
authors.initials: RV
authors.lastname: Roij
authors.affiliation: Physics of Fluids Group, Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.|Soft Matter and Interfaces Group, School of Engineering, RMIT University , Melbourne, VIC 3001, Australia.
authors.forename: Xuehua
authors.identifier: 0000-0001-6093-5324
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Physics of Fluids Group, Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Detlef
authors.identifier: 0000-0003-4138-2255
authors.initials: D
authors.lastname: Lohse