Measurement of Wood Wettability by the Wilhelmy Method. Part 2. Determination of Apparent Contact Angles

Abstract

This work focuses on the determination of apparent contact angles on wood by the Wilhelmy method. In this method, the force acting on an object is measured during a test cycle involving immersion in and withdrawal from a probe liquid. Fresh and aged veneers of extracted and non-extracted heart-and sapwood of pine were investigated. The results indicate that wicking of the probe liquids, into and along the porous wood veneers, occurs during the test cycles and that this strongly affects the determination of contact angles. It is suggested that two different wicking phenomena occur. First, when the veneer contacts the liquid, an instantaneous 'initial wicking' occurs. It is suggested that this initial wicking is influenced primarily by the liquid density and structural properties of the specimen (such as porosity and surface roughness), and not by surface energetics. An initial wicking constant was therefore estimated for the different veneer samples based on measurements in octane. Second, after the initial wicking, a continuing 'secondary wicking' is observed. In some cases, this may result in zero contact angle after a certain immersion depth. Contact angles should, therefore, be estimated from the initial part of the immersion, where the secondary wicking can be neglected. This may also reduce any contamination of the probe liquids by extractives. The Wilhelmy method seems to be a valuable tool for estimating the wetting properties of wood, permitting reproducible measurements of apparent contact angles provided that there is efficient control of wicking and contamination effects. KeywordsApparent contact angles Contamination Extractives Wettability Wicking Wilhelmy method Wood Brought to you by | University of Arizona Authenticated Download Date | 5/26/15 5:35 PM

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

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Wettability of waterborne coatings on chemically and thermally modified pine wood

“…8,[13][14][15] Immersing and pulling out a wood plate along its radial direction in a liquid allows determination of the advancing and receding contact angle. Due to the aim of this study (coating application), only the advancing contact angles were determined.…”

Chemical and Physical Parameters of Different Modifications of Rape Straw (Brassica napus L.)

“…Contact angle analysis is widely used to determine the wettability of solid materials (Walinder and Ström 2001;Aydin 2004). To determine wetting characteristics of modified particles, the contact angle of the water and particle surface was measured using a DSA 30E goniometer (Krüss GmbH, Hamburg, Germany).…”