title: Wetting hysteresis of nanodrops on nanorough surfaces.
abstract: Nanodrops on smooth or patterned rough surfaces are explored by many-body dissipative particle dynamics to demonstrate the influence of surface roughness on droplet wetting. On a smooth surface, nanodrops exhibit the random motion and contact angle hysteresis is absent. The diffusivity decays as the intrinsic contact angle (θ_{Y}) decreases. On a rough surface, the contact line is pinned and the most stable contact angle (θ_{Y}^{'}) is acquired. The extent of contact angle hysteresis (Δθ) is determined by two approaches, which resemble the inflation-deflation method and inclined plane method for experiments. The hysteresis loop is acquired and both approaches yield consistent results. The influences of wettability and surface roughness on θ_{Y}^{'} and Δθ are examined. θ_{Y}^{'} deviates from that estimated by the Wenzel or Cassie-Baxter models. This consequence can be explained by the extent of impregnation, which varies with the groove position and wettability. Moreover, contact angle hysteresis depends more on the groove width than the depth.
authors.affiliation: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Cheng-Chung
authors.initials: CC
authors.lastname: Chang
authors.affiliation: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Yu-Jane
authors.initials: YJ
authors.lastname: Sheng
authors.affiliation: Department of Chemical and Materials Engineering, National Central University, Jhongli 320, Taiwan.
authors.forename: Heng-Kwong
authors.initials: HK
authors.lastname: Tsao