DCAT – Dynamic Contact Angle
DCAT – Dynamic Contact Angle measuring devices and Tensiometer
The dynamic contact angle measuring devices and tensiometer of the DCAT series are universal measuring devices for the force-based measurement of interfacial parameters and phenomena. In the following you will learn about the possibilities that the tensiometry offers and about our DCAT models with their extensive range of accessories and intuitive software control.
Surface and interfacial tension
Surface tension acts to contract and minimise any liquid surface. If a surface is being enlarged by the formation of a liquid lamella, as a test body, such as a Wilhelmy plate or Du Noüy ring, is in contact with it, the surface tension exerts a tensile force that can be measured. Within a tensiometer this force is measured by a high precision weighing system and, hence, the surface tension of the liquid can be calculated.
Using a tensiometer, also the interfacial tension between two liquids can be measured with the help of a test body. Since tensiometry is based on force measurements it is – in contrast to the optical analysis of pendant drops – not necessary that one of the liquids is transparent or that the refractive index differs between the two liquids. Therefore, tensiometry is in many cases a handy alternative to the optical measurement of surface and interfacial tensions.
With tensiometry it is also possible to investigate the wetting of and dynamic contact angles on solid samples that are used as the test body. For this purpose the sample is dipped into a liquid with known surface tension and pulled back out again. In this case the weighing system detects both the buoyancy of the body and the lamella weight. During evaluation the buoyancy contribution is removed from the data so that the advancing angle can be determined for the immersion and the receding angle for the withdrawal based on the Wilhelmy equation. In addition, the advancing contact angle of powders and fibre bundles can be determined by the Washburn method.
Wide field of application
Other tensiometric methods, like the determination of liquid or solid density, utilise the measured buoyancy. DataPhysics Instruments offers specialised sample holder sets for this purpose. Other specific test bodies and accessory modules can be used in order to investigate sedimentation and penetration properties, adhesion or the surface pressure.
The Wilhelmy plate method is a well-established method for determining surface and interfacial tensions with a tensiometer. The method utilises a Wilhelmy plate as the test body. It is typically made of iridium–platinum and is a few centimetres in length and height. The plate is attached to the weighing system of the tensiometer and positioned at the liquid surface in such a way that a liquid lamella forms. The gravitational force of the lamella, which equals the perpendicular part of the tensile force caused by the surface tension, is measured. Together with the definition of the surface tension as tensile force per length of the contact line this yields the Wilhelmy equation:
Surfactants and CMC
Interfacially active compounds like surfactants consist of a hydrophilic and a hydrophobic part, hence they adsorb preferably at interfaces. There they reduce the surface or interfacial tension, respectively, which is essential for good washing performance or the stability of foams. The amount of surfactant molecules that can be accommodated on a certain surface area is limited. The only possibility for ‘excess’ surfactant molecules to shield their hydrophobic parts from water is by forming micelles.
The characteristic surfactant concentration that, when reached, initiates the formation of micelles is called “critical micelle concentration” (CMC). It can easily be determined with a measurement series that varies the surfactant concentration: below the CMC the surface tension decreases with increasing concentration because more and more surfactant molecules adsorb at the surface. Above the CMC, further added surfactant serves only to form micelles and the surface tension stays constant.
The DCAT Models
The dynamic contact angle measuring devices and tensiometer of the DCAT series are universal measuring devices, that allow to investigate numerous surface and interfacial properties (see introduction to tensiometry). Due to the compact and modular product design it is possible to find an individual and best suited combination of device model and accessories for any task.
Highest precision and reproducibility of the measuring results is guaranteed by well-established measuring techniques and weighing technology. Due to state of the art electronic components all DCAT models offer an especially fast and precise actuator, an automatic crash protection and can be operated intuitively via the TP 50 control panel.
For a compact overview of the DCAT models download the product brochure or use our convenient online comparison of the different models.
Measurements conforming to standards
Measurements that comply with various national and international standards are possible due to the high precision and extensive range of accessories of the DCAT models. These standards are among others:
- ASTM D971
- ASTM D1331
- ASTM D1417
- ASTM D1590
- DIN 53593
- DIN 53914
- DIN EN 14210
- DIN EN 14370
- ISO 304
- ISO 1409
- ISO 4311
- ISO 6295
- ISO 6889
- OECD 115
- IEC 62961
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