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 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.
Du Noüy ring with liquid lamella
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.
Contact angle measurement on powder
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.
Langmuir trough module LTM
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:
Wilhelmy plate with liquid lamella
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.
Surface tension as a function of the surfactant concentration
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.
The DCAT 9 is the powerful entry level model for the weight-based measurement of surface and interfacial tension and the density of liquids and solids. In order to measure temperature dependent properties the DCAT 9T features an integrated digital thermometer and a liquid temperature control unit TV 70.
The DCATSoftware is available in various independently usable modules. The available software modules for the DCAT 9 & DCAT 9T are:
Learn more about the DCATS modules.
Due to the modular product design the DCAT 9 / 9T can be combined with a multitude of options of the versatile DCAT accessories range. Learn more about the available accessories.
Determination of the surface tension using a DCAT 9 with Wilhelmy plate PT 11
DCAT 9T with liquid temperature control unit TV 70
The DCAT 15 enables additional measuring methods and hence can be used to determine dynamic contact angles, the surface energy of solids or sedimentation and penetration properties. In addition the DCAT 15 can be extended with a liquid dosing unit LDU 25 and can thus create sequential concentration series of, for example, surfactant solutions. Without manual user intervention the critical micelle concentration (CMC) can be determined software controlled in a series of experiments.
The DCATSoftware is available in various independently usable modules. The available software modules for the DCAT 15 are:
Due to the modular product design the DCAT 15 can be combined with a multitude of options of the versatile DCAT accessories range. Learn more about the available accessories.
DCAT 15 with LDU 25
LDU 25 with SH-LDU and RRS 25
The dynamic contact angle measuring device and tensiometer DCAT 25 is the multifunctional all-round instrument of the DCAT series. The weighing system is even more precise than that of the DCAT 9 and 15 and hence offers highest accuracy for the determination of surface and interfacial tension. A completely closed sample chamber enables measurements under inert gas or ionised atmosphere as well as with controlled relative humidity.
Due to the longer travel distance of the sample stage, an electrical temperature control unit can be mounted inside the DCAT 25 which makes measurements at temperatures of up to 250 °C possible. Moreover the Langmuir trough module can be used to investigate the surface pressure and the interfacial rheology of monolayers. The upgrade video system provides the opportunity to record video-sequences during force of adhesion measurements and to evaluate contact angle, contact area etc. in addition to the force. For an intuitive and fast device control even during complex measurements, a TP 50 control panel is included in the delivery of every DCAT 25.
The DCATSoftware is available in various independently usable modules. The available software modules for the DCAT 25 are:
Due to the modular product design the DCAT 25 can be combined with a multitude of options of the versatile DCAT accessories range. Learn more about the available accessories.
DCAT 25 with electrical temperature control unit TEC 250/DCAT
Application video: Water Adhesion on Plant Leaves
The DCAT 25SF incorporates a weighing system of highest accuracy with a resolution of 0.1 μg which allows to measure even on single fibres. As an ideal single fibre tensiometer the DCAT 25SF is not limited to this very special purpose due to the modular design of the product line.
The DCATSoftware is available in various independently usable modules. The available software modules for the DCAT 25SF are:
Due to the modular product design the DCAT 25SF can be combined with a multitude of options of the versatile DCAT accessories range. Learn more about the available accessories.
Measurement at a fibre with the DCAT 25SF