Abstract
Surface science, which includes the preparation, development and analysis of surfaces and coatings, is essential in both fundamental and applied as well as in engineering and industrial research. Contact angle measurements using sessile drop techniques are commonly used to characterize coated surfaces or surface modifications. Well-defined surfaces structures at both nanoscopic and microscopic level can be achieved but the reliable characterization by means of contact angle measurements and their interpretation often remains an open question. Thus, we focused our research effort on one main problem of surface science community, which is the determination of correct and valid definitions and measurements of contact angles. In this regard, we developed the high-precision drop shape analysis (HPDSA), which involves a complex transformation of images from sessile drop experiments to Cartesian coordinates and opens up the possibility of a physically meaningful contact angle calculation. To fulfill the dire need for a reproducible contact angle determination/definition, we developed three easily adaptable statistical analyses procedures. In the following, the basic principles of HPDSA will be explained and applications of HPDSA will be illustrated. Thereby, the unique potential of this analysis approach will be illustrated by means of selected examples.
Highlights
Introduction and Brief Summary of BasicWetting TheoriesInvestigating and analyzing the wetting behavior of solid surfaces has a long and controversially discussed history
Beside some experimental influence suchasasdrop drop displacement, drop volume, horizontal or inclined etc., influence quantities quantities such displacement, drop volume, horizontal or inclined set-up,set‐up, etc., contact contact angle determination depends on the image and analysis and fitting the used fitting procedure to angle determination depends on the image analysis the used procedure to extract the extract the contact angle from the experimental drop shape
Due to the generally non-axisymmetric drop profiles drop profiles on real surfaces,analyses commercial analyses such as ellipse‐fitting, or on real surfaces, commercial strategies suchstrategies as ellipse-fitting, circle-fitting orcircle‐fitting tangent-fitting tangent‐fitting approaches, mostly the whole shape, result in large inaccuracies, approaches, which mostlywhich consider the consider whole drop shape,drop result in large inaccuracies, especially especially for extreme wetting situations such as low contact angle surfaces, superhydrophobic and rose petal surfaces, which might lead in the worst case even in misinterpretations and misleading concepts presented in the scientific literature
Summary
Investigating and analyzing the wetting behavior of solid surfaces has a long and controversially discussed history. Kamusewitz and Possart [47] proposed an empirical model to determine the equilibrium contact by measuring advancing and receding contact angles on different rough low-energy surfaces They proposed a linear relationship between surface roughness and contact angle hysteresis resulting in Equations (10) and (11), θa = θY + A a × ∆θ (10). By determine the roughness factor by, e.g., scanning force microscopy, the equilibrium contact angle can be calculated by using the Wenzel Equations (1)–(7) At this point one critical fact has to be stressed that is the chemical heterogeneity of a real surface, which is highlighted in the cited contributions. Thereby, drop shape extraction, static, dynamic and statistical contact angle analyzes will be presented by examples of real smooth surfaces, contact angle hysteresis, dynamics of wetting, wetting on rough and chemically heterogeneous surfaces, superhydrophobic and rose petal-surfaces, nonstick droplets and sticking droplets (ionic liquids)
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