A sessile drop refers to a liquid droplet that’s placed on a solid surface. The term stems from Latin sessilis, meaning “sitting,” emphasising that the drop remains stationary on the substrate. It’s literally attached at its base, offering a stable configuration for optical analysis.
The sessile drop method is a technique we very commonly use for measuring the contact angle of a liquid on a solid surface, which indicates the surface’s wettability. In this method, a small droplet of liquid is placed on a flat, horizontal solid substrate, and the angle θc formed between the liquid-gas interface and the solid-liquid interface at the contact point is measured, typically using an optical tensiometer.
This sessile drop method is foundational in surface science because it provides a simple, precise way to quantify how a liquid interacts with a material. The method is typically non-destructive, and can be used with a wide range of solid surfaces and liquids. Using our instrumentation, the method provides precise measurements of contact angle. It can also get complicated, by measuring changes in contact angle over time to study dynamic wetting behaviour or surface modifications.
Contact angle measurement provides essential insights if you are using or developing adhesives, inks or coatings. You can assess the efficacy of cleaning or surface preparation methods. It’s central to assessing wettability, surface energy, and optimising adhesion.
