(616h) Influence of Surface Asperities and Surface Energetics on Wetting Characteristics of Spherical Glass Beads

The microstructures of low surface energy materials give unique wetting characteristics of materials. Thus, the study of biomimetic surfaces is a very active research area in the present literature. However, in most of the existing studies, the flat hydrophobic surfaces are micro-fabricated in a controlled manner to prepare the super-hydrophobic surfaces (contact angle ≥ 150̊ ). In this work, chemical etching is used to tune the surface roughness of spherical glass beads in a random manner by varying the etching time (15, 30, 45, 60 and 90 min). The wetting characteristic of original and surface-modified glass beads is studied using contact angle measurement by the sessile drop method. The change in surface morphology, surface composition and surface energetics is characterised by Atomic Force Microscope (AFM), X-ray Photoelectron Spectroscopy (XPS), and Surface Energy Analysis (using OWK method) respectively. The modified glass beads surface display super-hydrophobic behavior with water contact angle 148˚ for 90 min etched glass beads with respect to the original glass beads (79.6 ˚). In addition, tilting surface method shows that etched surface can hold water droplet even if it is turned upside down, showing strong solid-liquid adhesion at the interface. The AFM and XPS result shows that the change in the wetting behavior of modified glass beads is mainly due to the combined effect of surface chemistry and surface profile (more regular and dense distribution of asperities). Results reveal that the closely distributed surface asperities with low aspect ratio lead to the high contact angle at the solid-liquid interface of surface-modified glass beads. In addition, the increased non-bridging oxygen at the etched surface leads to strong adhesion at the solid-liquid interface. The effective contact angle at the surface of etched glass beads is determined using the solid-liquid fraction derived from geometric parameters of the substrate and surface energy approach (spreading coefficient). Results indicate that the change in surface features leads to larger contact angle (≈150̊) and adhesive liquid drop at the etched surface is in Cassie impregnation regime.