Tensiometric Characterization of Superhydrophobic Surfaces As Compared to the Sessile and Bouncing Drop Methods

Abstract

We have considered in this work the Wilhelmy plate tensiometer to characterize the wetting properties of two model surface textures: (i) a series of three superhydrophobic micropillared surfaces and (ii) a series of two highly water-repellent surfaces microtextured with a femtosecond laser. The wetting forces obtained on these surfaces with the Wilhelmy plate technique were compared to the contact angles of water droplets measured with the sessile drop technique and to the bouncing behavior of water droplets recorded at a high frame rate. We showed that it is possible with this technique to directly measure triple-line anchoring forces that are not accessible with the commonly used sessile drop technique. In addition, we have demonstrated on the basis of the bouncing drop experiments wetting transitions induced by the specific test conditions associated with the Wilhelmy plate tensiometer for the two series of textured surfaces. Finally, the tensiometer technique is proposed as an alternative test for characterizing the wetting properties of highly liquid-repellent surface, especially under immersion conditions.

Role of Trapped Air in the Attachment of Staphylococcus aureus on Superhydrophobic Silicone Elastomer Surfaces Textured by a Femtosecond Laser

“…The table in Figure B gives the dynamic contact angles of MHB at 37 °C measured with a Wilhelmy plate tensiometer on the smooth silicone elastomer and the two textured surfaces, R1 and R2, before and after UV/ozone treatment. As already demonstrated with water, the R1 surface before the UV/ozone treatment shows the highest advancing and receding contact angles ( θ a = 147° and θ r = 128°) for MHB (i.e., lowest contact angle hysteresis of Δθ = 20°). This result demonstrates a low affinity between the liquid and the surface, associated with remarkable air retention, as previously suggested from the qualitative characterization of the surface wettability shown in Figure .…”

“…The advancing and receding contact angles θ a and θ r are then calculated following θ = arccos [(F w /(pγ)]. A detailed description of the exploitation of these measures and related calculations are given in the works of Hisler et al 55 and Kleingartner et al 57 The difference between the advancing and receding capillary forces corresponds to the wetting hysteresis (i.e., the contact angle hysteresis Δθ).…”

“…In the frame of this study, a much more relevant technique to determine the wetting properties of these superhydrophobic surfaces is the use of a Wilhelmy plate tensiometer. Although rarely used with highly liquid-repellent surfaces, − this technique allows the wetting behavior of immersed surfaces to be modeled, which is representative of many conditions of use, for example, particularly in the frame of this study, those of a bacteria culture. Additionally, this technique allows the temperature of the liquid to be considered much more easily than the sessile drop technique (the bacterial culture in our experiments was at a temperature of 37 °C).…”

“…Moreover, the Wilhelmy plate tensiometer allows measurement of the wetting properties under immersion conditions at a controlled temperature, which is particularly relevant to this study, as the surfaces are immersed in a medium at 37 °C during the bacterial culture. In contrast with the sessile drop, this technique gives much more precise information about the air trapping, which has been suggested as a possible origin of the antibacterial properties of superhydrophobic or medium repellent surfaces. − This hypothesis is addressed later in this article by making these surfaces textures superhydrophilic and fully wetted by the culture medium (MHB) through UV/ozone treatment (i.e., without air trapping).…”

Bacterial Colonization of Low‐Wettable Surfaces is Driven by Culture Conditions and Topography

“…These two complementary approaches to the sessile drop method display the specific hydrostatic and confinement conditions associated to a sample completely immersed in liquid. [ 51,52 ] Such a resistance to wetting describe the 100% PFDA (ppPFDA) surface as a superhydrophobic, with significant air trapping. Finally, the range of coatings is composed of hydrophobic surfaces in Wenzel state (without trapped air) (%PFDA up to 80%), superhydrophobic surfaces with a mixed Wenzel and Cassie–Baxter state (%PFDA from 80% to 95%) and superhydrophobic surface in Cassie–Baxter state (with trapped air gradient) (%PFDA of 100%).…”