DCAT 21 (Dynamic Contact Angle Meter and Tensiometer)

Instumentelle Analytik (Umwelt- und Bodenchemie)

 

Model:

Dynamic Contact Angle Meter and Tensiometer DCAT Serie 21 (DataPhysics)

Application

Determination of static and dynamic contact angles of solids, of static and dynamic surface and interfacial tensions of liquids and of the critical micelle forming constant using Modified Washburn Method, Wilhelmy Plate Method or Du Noüy Ring Method.

Theory

When a solid is brought in contact with a liquid beside the gravity, the interfacial tensions of the three adjacent phases (liquid-gas (liquid surface tension), solid-gas (solid surface energy), solid-liquid) are acting at the three-phase-line. In equilibrium (e.g. at a sessile drop) the sum of the resulting forces equals zero. Therefore, close at the three-phase-line the liquid surface forms a lamella such that the difference between solid-gas tension and solid-liquid tension is equilibrated and forms the contact angle between solid-liquid and liquid-gas tension which is typical for the wetting of the respective solid and liquid. If a solid is suspended from a balance and immersed into a liquid of known surface tension by raising the liquid level, the contact angle can be calculated from the change in weight of the solid minus the buoyancy (Dynamic contact angle by Wilhelnmy Plate Method). If instead of the solid sample a well characterised Platin-Iridium-Plate is used in the same way the surface tension of an unknown liquid may be calculated. In a porous sample in contact with a liquid, capillary forces will induce capillary rise of the liquid into the sample. The increase in weight can be used to calculate the contact angle under the condition that the solid has a contact angle lower than 90° and the sample porosity may be determined by an ideal wetting liquid with a contact angle of zero for the respective solid (e.g. n-hexane). For the Du Noüy Ring Method, immersing and emerging a Platin-Iridium ring from or into liquid results in the formation of an outward pulled or inward pushed lamella. The point, where the gravity force of the lamella or the bouyouance overcomes the surface tension is determined by a continuous recording of changes in weight of the ring during pushing and pulling.

Description

The DCAT 21 consists of a high performance electro-dynamic compensation balance (0.1 mg – 210 g ± 0.01 mg) with auto calibration function and enables a measuring range of 1 – 1000 mN/m; ± 0.001 mN/m. The software controlled motorized height positioning of the sample vessel works with variable speed (0.7 µm/s – 500 mm/min) and has a maximum lifting range of 105 mm and a position resolution of 0.1 µm. Integrated is a digital thermometer and temperature control electronics which together with an external thermostat allows working under constant temperature conditions. Accessories like a Du Noüy ring RG 11,(platinum-iridium, DIN 53914), a Wilhelmy plate PT 11 (platinum-iridium, DIN 53914) as well as sample holders for glass tubes for powdered samples and sample plates (microscope glass slides), and sample vessels for liquids of borosilicate glass available with diameters 50 and 70 mm allow the conduction of the Modified Washburn method, the Dynamic Wilhelmy method, the Wilhelmy Plate method and the Du Noüy Ring method.