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Contact angle measurements from the contact diameter of sessile drops by means of a modified axisymmetric drop shape analysis

Authors
Journal
Journal of Colloid and Interface Science
0021-9797
Publisher
Elsevier
Publication Date
Volume
130
Issue
1
Identifiers
DOI: 10.1016/0021-9797(89)90074-x
Disciplines
  • Biology

Abstract

Abstract This paper presents a novel approach to measuring contact angles. The Axisymmetric Drop Shape Analysis-Contact Diameter (ADSA-CD) approach determines the contact angle by solving the Laplace equation of capillarity numerically, and using as input parameters the liquid surface tension, the drop volume, and the contact diameter of the drop. The contact diameter is the main experimental parameter to be determined as the liquid surface tension is known and the volume of the sessile drop is determined by means of a precision micrometer syringe. Various strategies for the determination of the contact diameter are possible, ranging from a simple measurement by means of a travelling microscope to digital image analysis determining the contact area and hence an effective contact diameter. An accuracy in contact angles of ±0.5° is readily obtainable for well-prepared surfaces. Indications are that the technique will be limited only by the quality of the solid substrate and hence the deviations of the contact circle from circularity. While the technique is applicable to any contact angle, in this paper, only contact angles of less than 90° were measured. The technique performs particularly well for small contact angles below 20°, where other techniques, such as the analysis of drop profiles, produce rather large errors. The method is therefore expected to be particularly useful for the study of usually very hydrophilic biological specimens.

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