Volume-19 (05/2008)
Measuring with air, the first: Bubble Pressure Tensiometer BP100
A further development of the bubble pressure technology at KRÜSS
Printing - adhering – spraying – cleaning - coating: processes like these require surfactants that are effective even after a few fractions of a second. The Bubble Pressure Tensiometer BP100 determines the dynamic surface tension as a function of the age of the surface. The instrument thus provides crucial information about wetting and drop formation in rapid processes.
- Bubble Pressure Tensiometer BP100
What it can do
- Measure the dynamic surface tension at a constant or changing surface age
- Enormous range of variations in surface age: 5 ms (highly dynamic) to 100 s (virtually static)
- Fully automatic measuring procedure thanks to software-controlled capillary immersion
- Determination of adsorption and diffusion coefficients
- Built-in compressor – no compressed air connection required
In addition to the dynamic surface tension, the method also provides the equilibrium value of the surface tension calculated according to Hua & Rosen. If the surfactant concentration is known then the diffusion and adsorption coefficients can be calculated – important parameters for the mobility of surfactants. Measurements at constant bubble age allow further conclusions to be drawn, for instance for concentration and temperature comparisons.
How it works
A software-controlled flow of air uses a capillary to generate air bubbles in the sample. A pressure sensor determines the maximum pressure during bubble formation; the surface tension is calculated from this. Thanks to the built-in compressor the instrument works without any external compressed air supply. Software-controlled scans at virtually any resolution can be made automatically over a wide surface age range.
- Dynamic surface tension of a surfactant concentration series
After a minimal preparation period the measurement takes place fully automatically up to data output in the form of a plot. With a mouse-click the measuring parameters, results and evaluations appear in a comprehensive report. Thanks to the LabDesk™ software platform for all KRÜSS Tensiometers data from other types of instrument can be managed in joint projects.
Where it is used
Everywhere that surfactants are used:
- Surfactant development
- Optimization of spraying processes
- Development of washing powders and detergents
- Optimization of painting, printing and coating processes
- Checking electroplating bath concentrations
- Improvement of rapid wetting processes
Measuring with air, the second
Sample Holder Set ST10 for contact angle measurements by the captive bubble method
The Sample Holder Set ST10 turns everything on its head: the contact angle is not measured on the sample but beneath it in a surrounding liquid phase. The deposited “drop” is an air bubble.
- Air bubble under an immersed solid surface
In this arrangement, known as captive bubble, wetting is measured indirectly, i.e. by using the dewetting on contact with the air bubble. An important field of application is the measurement on contact lenses; one of the sample holders in the ST10 Set is constructed for this purpose. Because of their hydrogel structure, soft lenses must always be kept in a liquid and therefore cannot be measured by drop deposition in air.
- Sample Holder Set ST10 with cuvet, special needle and holders for various samples
The two other holders in the set are used for working with film/foils or textiles as well as with rigid samples. There are two cases in particular for which the captive bubble method comes into question. The first concerns materials with a fibrous or corrugated surface. Such samples can often be smoothed by pre-wetting, so that in the subsequent measurement using the bubble no interferences occur at the phase contact point. In absorbent materials the captive bubble method is frequently the only way in which a stable contact angle value can be obtained.
The second case concerns samples with a high surface free energy which, because of their very small contact angle, can hardly be studied by the standard method of the sessile drop. In contrast, the complementary angle of the air bubble is very large and can easily be measured.
The set not only allows the deposition of air bubbles, but also of drops of a lighter liquid phase in a heavier phase. This arrangement is also usually used for studying high-energy surfaces, for example in the determination of the surface free energy according to Schultz.
The Sample Holder Set ST10 is available immediately as an accessory for all stationary KRÜSS contact angle measuring instruments.
Application Reports on the subject:
Issue 12 | 03/2006: Surface free energy measurements on textiles
Issue 14 | 09/2006: Methods for wetting measurements on hydrogels
Sociable software: DSA3 with the “Remote-Control-API” interface
DSA3 has learned to speak. Thanks to a new software interface, the DSA3 Remote Control API, the contact angle software can communicate with other software tools and, for example, make its contribution in laboratory networks.
With the help of the drop shape analysis software DSA3 complete measuring procedures – from drop positioning through deposition and control of the optics up to drop shape analysis and data storage – can be programmed and carried out. Thanks to the new DSA3 Remote Control API interface such procedures can also be called up by other applications and the measuring data transferred automatically.
In practice it works like this: the automatic procedures are prepared in the DSA3 software. The DSA3 is then remotely controlled via the Remote Control API interface: a program to be generated by the user then selects the required measuring procedure and starts the measurement. In return the DSA3 delivers the obtained measuring data to the user software. As a result of the handshake between the programs new drop shape analysis applications are opened up: for example, samples placed in position by a robot can be automatically measured.
- All a question of protocol: handshake with customer software
Thanks to the Remote Control API contact angle measurement can be linked to almost any conditions that are defined in the user software – for example the timing, messages from sensors or data from other instruments. The returned results can be recorded, saved and visualized in a manner defined by the user. It is ideal for use in laboratories with a large data throughput, particularly when complex relationships between the contact angle and a large number of other chemical and physical parameters are to be studied.