Capillary Bridges on Hydrophobic Surfaces: Analytical Contact Angle Determination

Nagy, Norbert (2022) Capillary Bridges on Hydrophobic Surfaces: Analytical Contact Angle Determination. LANGMUIR, 38 (19). pp. 6201-6208. ISSN 0743-7463

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Abstract

The capillary bridge probe method was introduced previously as a high accuracy contact angle determination method relying capillary bridges on hydrophilic and superhydrophilic surfaces. [Nagy, N. Contact Angle Determination on Hydrophilic and Superhydrophilic Surfaces by Using r–θ-Type Capillary Bridges. Langmuir 2019, 35 (15), 5202–5212.] In this work, the behavior of r-θ type liquid bridges was studied and the contact angles were determined on hydrophobic surfaces. The equilibrium shape of these liquid bridges often does not contain the neck or haunch region. The unknown neck/haunch radius prevents analytical evaluation of the capillary bridge shape. In this work, the possible incomplete liquid bridge shapes were classified and a novel procedure was developed for the Delaunay’s analytical solution based evaluation of these states. The parameter space of the capillary bridges was visualized and described without using dimensionless variables. As a demonstration, Cyclo Olefin Polymer and PTFE surfaces were investigated, advancing and receding contact angles determined and compared to the results of sessile drop measurements.

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