Contact angle hysteresis on rough hydrophobic surfaces
ABSTRACT In this short note, we report a quantitative investigation of the hysteresis of the Cassie and Wenzel drops on a given rough surface. The Cassie drop shows much less hysteresis compared to a Wenzel drop and is therefore preferred in applications involving moving droplets. The experimental measurements are compared with the various theoretical models for the apparent contact angles and recommendations are made.
- SourceAvailable from: Il-Joo Cho[Show abstract] [Hide abstract]
ABSTRACT: A large number of silicon (Si) patterns consisting of nanopillars of varying diameter and pitch have been fabricated and further coated with diamond-like carbon (DLC) and perfluoropolyether (Z-DOL) films. The wetting behavior and nano-adhesion/friction of the patterns are investigated experimentally in relation to the nanostructures and the hydrophobicity of the materials. Measurements of water contact angle illustrate that the patterning-enhanced wettability of the Si flat surface, along with two distinct wettings which are in good agreement with the Wenzel and hemi-wicking states, depended on the value of the pitch-over-diameter ratio. In the case of the coated patterns, three wetting states are observed: the Cassie-Baxter, the Wenzel, and a transition from the Cassie-Baxter into the Wenzel, which varies with regard to the hydrophobic properties of the DLC and Z-DOL. In terms of tribological properties, it is demonstrated that a combination of the nanopatterns and the films is effective in reducing adhesive and frictional forces. In addition, the pitch and diameter of the patterns are found to significantly influence their adhesion/friction behaviors.Nanotechnology 09/2011; 22(39):395303. · 3.84 Impact Factor
- Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2014; 443:567-575. · 2.11 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The behavior of drops on superhydrophobic surfaces is of interest from an engineering point of view. As it can be difficult to probe some of the more subtle phenomena by experiment, numerical simulations can be illuminating. Many research efforts have utilized the lattice Boltzmann method to glean important conclusions about the nature of this subject, but only few have done so while eliminating the phenomenon of spurious currents and employing drop densities greater than approximately ten times that of the gas density. This paper presents a new implementation of boundary conditions for the complex geometry found in simulations of drops on superhydrophobic surfaces, which extends an existing model that has been shown to eliminate spurious currents. We validate our model by comparison with experiments, and demonstrate that spurious currents are eliminated for the density ratio encountered in a water/air system. We further discuss the issue of numerical resolution for a problem that possesses such a naturally large separation of scales, and we present a comparison between two- and three-dimensional simulations. We find that an adequate resolution, which may be difficult to achieve, must be given to capture the appropriate transition from the Cassie to the Wenzel state for the case of forced wetting under gravity. Furthermore, the form of our boundary condition may be extended to cover other types of complex geometry not included here.Journal of Computational Physics 10/2013; 250(1):601-615. · 2.14 Impact Factor