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Surface properties of wood and stones are very important in influencing the bonding and finishing of wood and for road construction. Two important surface properties are wettability and surface free energy. Contact angle measurement is a simple, useful and sensitive tool for quantifying the wettability and the surface energy of different materials in contact with pure water and/or aqueous surfactant solutions. Nevertheless, a sessile drop on a real surface shows different contact angle values due to its lack of symmetry or to the loss of volume by capillary action. For this reason alternative techniques which supply an average contact angle value are required. In view of this fact, we applied axisymmetric drop shape analysis-diameter (ADSA-D) using a top view of a sessile drop and axisymmetric drop shape analysis-profile (ADSA-P) with a side view of a captive bubble. Both techniques calculate the contact angle by solving the Young–Laplace equation although with different algorithms, the former needs the maximum drop diameter while the last makes use of the complete bubble profile. ADSA-D was applied to study two wood species (eucalyptus and pine) and ADSA-P with polished rocks of two different compositions (silicate and calcite). The maximum contour of the drop was fitted to an ellipse after being detected and extracted by means of a semi-automatic procedure of image processing. Thus, two different contact angles were found out. The captive bubble method in conjunction with the current ADSA-P technique allows to obtain comfortable, automatic and reproducible measurements of contact angle on porous stones.

Π/ A isotherms of spread l -DPPC ( l -dipalmitoyl phosphatidylcholine) layers were determined up to the over-compressed state by using the captive bubble method. The influence of solvent vapour in the gas phase on the interfacial behaviour of monolayers was studied as traces of the spreading solution usually stay in the bubble. This was done for two cases; the pendant drop technique with spread 1-monoglyceride monolayer, where the partial pressure of solvents remains constant, and the captive bubble with spread l -DPPC layers, where the partial pressure increases during monolayer compression. Two cases of spreading solvents are distinguished: solvents, which do adsorb at the interface (chloroform), and those, which do not (heptane). Using a model, which takes into account only a small number of accessible parameters, the influence of none adsorbing solvents can be sufficiently described by an increasing cohesion pressure when the partial pressure remains constant. The influence of polar solvents may be quantified by a factor, which considers the apparent increase of the minimum molecular area demand. Spread DPPC monolayers determined by the captive bubble technique show a plateau in the range of about 50 mN m −1 , which depends on the amount of spreading solvent in the atmosphere of the bubble. By monolayer compression, the solvent molecules are squeezed out of the monolayer. Over-compression of the DPPC monolayer occur when all solvent molecules are removed and the surface tension further decreases down to almost zero. In contrast to monolayer collapse the surface pressure do not decrease abruptly for DPPC-layer expansion. This was explained by a monolayer-folding. Both, the process of squeezing out solvent molecules and the over-compression are accompanied by an apparent loss of DPPC molecules, indicated by a shift of the Π/ A isotherms to higher surface coverage. Monolayer cycling leads to a stepwise decrease of solvent molecules in the bubble atmosphere. The solvent molecules are assumed to be irreversibly incorporated into collapsed and lamellar structures, which may be formed by monolayer folds. Over-compressed collapsed or folded structures may be packed together and removed from the interface by forming visible particles. Lamellar structures are discussed as preliminary forms of liposomes, which may also incorporate solvent molecules, remove them during monolayer expansion from the interface, and causing an apparent loss of lipid molecules.

Contact angle measurements with captive bubbles have been used to quantify the wettability of different cellulosic materials in contact with pure water or aqueous protein solutions. The application of a new contact angle technique (axisymmetric drop shape analysis) in combination with atomic force microscopy permits new insights into the wetting behaviour of these hydrophilic surfaces. It was found that the unmodified cellulose membrane has a very smooth and homogeneous surface in the water-swollen state. There is almost no hysteresis between the advancing and receding water contact angles. The chemical modification of the cellulose with diethylaminoethyl groups results in a smooth but heterogeneous water-swollen membrane surface with fewer hydrophilic properties. A water-swollen cellulose acetate film was used as a model surface for wetting measurements with buffered protein solutions. It was found that different proteins (human serum albumin, fibrinogen) yielded different contact angles in their adsorbed state; after the adsorption of fibrinogen the contact angle of the pure aqueous buffer solution on the cellulose acetate was lower than the contact angle measured after the adsorption of human serum albumin.