Applications - What is the Contact Angle?
By placing a liquid droplet on a specimen surface, a contact angle θ is formed at the interface between the liquid and the substrate. By definition, a droplet which 'beads up', is non-wetting and a contact angle higher than 90 degrees is displayed. When the droplet 'wets out' across the surface, wetting is obtained and the contact angle is less than 90 degrees.
Contact angle measurement is a reliable method to characterize the interaction between a liquid and a surface. This robust method (Young-Laplace), established long time ago, has gained wide acceptance in surface science for applications related to:| Printing | Agriculture | Paper | Detergents | Corona treatment | | Coating | Pharmacy | Board | Inks | Flame treatment | | Adhesion | Biomedicine | Wood | Oils | Surface sizing | | Cleaning | Papermaking | Metals | Surfactants | Surface tension | | Absorption | Cosmetics | Plastic | Water | Surface contamination | | Wettability | Dentistry | Textile | Solvents | Surface energy |
When the liquid droplet does not penetrate into the substrate (e.g. water on glass) the interaction can be characterized by the static contact angle if the surface is smooth and homogeneous. When the liquid penetrates into or spreads across the specimen surface the interaction can be characterized by the dynamic contact angle as a function of time. The wetting hysteresis of a surface is characterized by the advancing/receding contact angles describing the wetting/de-wetting properties of a surface.
The contact angle is a function of the liquid's surface tension and the surface 'free' energy of the substrate.
|
 |
|
