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Interface Science and the Formation of Structure
Published in Jeffrey P. Simmons, Lawrence F. Drummy, Charles A. Bouman, Marc De Graef, Statistical Methods for Materials Science, 2019
Moreover, a wetting transition (from “non-wetting” to “wetting”) may occur as either a first-order (characterized by a discontinuous change in one or more state variables of the system such as entropy and volume) or continuous (i.e., no discontinuity in state variables upon transition) transformation upon the change of a thermodynamic state variable [115]. Here, several notes should be made. First, the term “perfect wetting” or “complete wetting” is sometimes used to avoid ambiguity because the term “partial wetting” (which is rigorously “non-wetting”) is used practically for a case where the contact angle (the angle α in Figure 10.3(a)) is less than 90° . Second, the superscript “(0)” in γαβ(0) refers to a hypothetical α−β interface (without the wetting ω phase or any adsorption) but not the equilibrium γαβ; at a thermodynamic equilibrium, however, this hypothetical α−β interface is replaced by an α−ω interface and an ω−β interface; by definition, the equilibrium interface energy for the α−β interface is given by:
Internal-Flow-Mediated, Tunable One-dimensional Cassie-to-Wenzel Wetting Transition on Superhydrophobic Microcavity Surfaces during Evaporation
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
Prashant Pendyala, Hong Nam Kim, Harpreet S. Grewal, Uikyu Chae, Sungwook Yang, Il-Joo Cho, Simon Song, Eui-Sung Yoon
The depinning pressure (∆Pdepin) and sag pressures (∆Psag) for the patterned surfaces were much larger than the typical Laplace pressure values. Ideally, such surfaces are not expected to show any wetting transitions unless external force or pressure is applied. Furthermore, the dominant mechanism of wetting transition depends on the magnitudes of ∆Pdepin and ∆Psag for the corresponding surfaces. For all the FDLC-coated surfaces, ∆Pdepin < ∆Psag (Table 1). Whereas, for PTFE-coated surfaces, ∆Pdepin < ∆Psag when microcavities were smaller than 20 µm. For PTFE-coated P20 and P40 surfaces, ∆Pdepin > ∆Psag. That is, except for PTFE-coated P20 and P40 surfaces, for all the remaining surfaces depinning of the air-water interface at the sidewall of the cavity is believed to be a main reason for the wetting transition (Figure S1). By comparing the magnitudes of ∆Pdepin and ∆Psag for each of the surface, the threshold pressure at which cavities on them are expected to exhibit wetting transition is clearly indicated in Table 1. From here on, this threshold pressure for wetting transition is referred to as ‘wetting pressure’ of the corresponding surface.