The Liquid Needle is an extremely thin jet of liquid which is created through a dosing nozzle using pressure. The dynamics are just sufficient to form a continuous stream of liquid while dosing, but small enough to avoid influencing the contact angle.
Dosing can be carried out much faster (< 0.1 s) with the Liquid Needle compared to a solid needle. Due to standardized dosing conditions, the dynamics and thus the reliability of the method are independent from decisions of the user. Furthermore, dosing drops on very hydrophobic samples is easier because the drop does not have to detach from another media (the needle).
The validity of the Liquid Needle method compared to the classic solid needle was proven in a thorough scientific study in which contact angles were measured on a broad range of samples, giving the same contact angle results for both dosing methods.
- Ming Jin, Raymond Sanedrin, Daniel Frese, Carsten Scheithauer, Thomas Willers: Replacing the solid needle by a liquid one when measuring static and advancing contact angles. Colloid and Polymer Science 294(4), 657-665, DOI 10.1007/s00396-015-3823-1 (2016).
- A summary of this article is presented in our Application Report AR728.