Effect of Needle and Dosing Parameters on Contact Angle Hysteresis Measurements

Contact Angle Hysteresis (CAH), a fundamental metric for characterising surface wettability, provides insight into intimate solid-liquid interactions. The widely used optical needle method inflates and deflates a droplet to measure the resulting CAH. Multiple factors can influence CAH results, but a standard has yet to be established to ensure consistent and accurate results between studies.



This work uses an optical drop-shape analysis to examine how needle and dosing parameters affect the CAH measurement. The study assesses the needle-droplet interaction at the triple-phase contact point and its potential impact on the droplet shape during CAH characterisation, which consequently affects the baseline contact angle measurement and the contact line dynamics.



Investigated variables include dosing flowrate, needle diameter, and material varying from hydrophilic stainless steel to superhydrophobic Glaco-coated needles. The objective is to determine the individual and combined effects of needle and dosing parameters on CAH measurements when using deionised water droplets on a smooth, uncoated hydrophilic silicon wafer and one which is coated with a hydrophobic self-assembled monolayer, perfluorodecyltrichlorosilane (FDTS).



This ongoing fundamental investigation holds promise for establishing a refined methodology and comprehensive protocol for precise CAH measurements, enabling researchers to achieve more accurate and repeatable data when characterising surface-wetting studies.