THE TRACKER
AUTOMATIC DROP TENSIOMETER FOR THE MEASUREMENT OF THE RHEOLOGICAL CHARACTERISTICS OF THE INTERFACES

The interfacial tension (for the liquid/liquid interfaces) or the surface tension (for the liquid/gas interfaces) is measured using the pending drop method.

A deformation of the area of the interface, by a dilatation or contaction of the volume of the drop, generates a varition of the interfacial concentration of the surfactant adsorbed on the interface, then a response of the interfacial tension which is recorded by the TRACKER. This response describes the rheological behaviour of the interface. By analogy with the solid bodies, this behavior is called viscoelastic. It is generated by the properties of the surfactants on the interface.

The instrument can create periodic deformations of the area of the interface over periods of time (ex: through sinusoidal variations of the volume of the drop) and automatically calculate the evolution of the  viscoelastic properties of the interfaces with time.

The  viscoelastic properties of the interfaces are among the key parameters which are correlated to the stability of the emulsions and foams.

Their evolution with time makes it possible to predict their short term and long term stability and to put in evidence a lot of interfacial phenomena which are commonly known as ageing of the interfaces.

Beyond these performances, the TRACKER can be fitted with several requisites and peaces of softwares allowing the implementation of dynamic measurements in very different experimental conditions.

Several publications give its description. Ex:

Viscoelastic proporties of triacylglycerol/water interfaces covered by proteins

J. BENJAMINS, A. CAGNA, E.H. LUCASSEN-REYNDERS
Colloid and Surfaces 114 (1996) 245-254

Surface dilational rheology of proteins adsorbed at air/water and oil/water
interfaces J. BENJAMIN, E.H. LUCASSEN-REYNDERS
Proteins at liquid interfaces (1998) 341-384

Oil-drop tensiometer applications for studying the kinetics of lipase action
S . LABOURDENNE, A. CAGNA, B. DELORME, G. ESPOSITO, R. VERGER
METHODS IN ENZYMOLOGY Vol.286 (1997) 306-326

Surface dilatational rheology of proteins absorbed at Air/Water and Oil/Water Interfaces
N. Puff, A. Cagna , V. Aguié-Béghin, R. Douillard
Journal of colloid and interface science 208 (1998) 405-414
 

Many others publications are published :
PUBLICATIONS-TRACKER

SOME KEY FEATURES

• measurement from low to high interfacial tensions (from less than 0,1 mN/m to more than 100 mN/m),

• liquid/solid/air ou liquid/liquid/solid contact angle measurement,

• fully automated and running under WINDOWS,

• computer assist settings,

• no correction factor required,

• small sample volumes required,

• friendly instrument and strongly built,

• several options allowing the execution ofmeasurements in very different experimental conditions.

DROP TENSIOMETER PRINCIPLE

Description of the instrument

1 - Driver of the piston of the syringe

2 - Cell with the sample

3 - Light source

4 - Lenses and CCD camera

5 - Computer

1 Driver of the piston of the syringe

The drop is formed at the tip of a capillary fitted to a syringe, whose piston is driven by a motor. The verticality of the tip of the capillary can be set in order to form axisymetric drops. This setting is computer assist.

The capillary is straight in the pending drop configuration and U-shaped in the rising drop configuration. This flexibility offered by the instrument makes it possible to cope with almost all the liquid densities and opacities.

The drop is automatically formed. The user has just to define its volume and its formation speed.

The syringes and capillaries are standard and quite available on the market (Exmire, Hamilton, etc.). Selecting their sizes makes it possible to form either small drops (less than 1 µl) or large drops (several hundreds of microliters).

As for the cuvette, the syringe is thermostated using a circulating bath. Different requisites are availables or implementing measurements at higher temperatures (up to 200°C) and/or pressure.

These performances are not limitations. Please ask us for specific requirements.

2 Cell with the sample

As for the syringe, the cuvette  is thermostated using a circulating bath. Different requisites are availables or implementing measurements at higher temperatures (up to 200°C) and/or pressure. 

Measurements of surface tension can also be implemented in saturated atmosphere.

These performances are not limitations. Please ask us for specific requirements.

3 Light source

The light source is integrating sphere type, which gives a homogeneous illumination in all the directions of the space.

This design gives a uniform enlighting of the drop, then a homogeneous contrast of the image of its contour on the light background.

4 Lenses + CCD Caméra

The lenses are telecentric type, so that the magnification of the optical system does not depend on the distance between the lenses and the drop. Then the optical calibration can be made once for all when it shall be made before any experiment with any other type of lenses.

Its optical distorsions are low. However the software implements a last optical correction in order to get the highest accuracy on the shape of the contour of the drop.

This design gives the instrument a high flexibility and makes it friendly of use, with the highest mesurement accuracy of the interfacial tension.

The CCD camera meets the CCIT standards (640x512 pixels) and grabs 25 images per seconds.

5 Control of the instrument

L'ensemble du tensiomètre est piloté à partir d'un micro ordinateur compatible PC. Cet ordibnateur est équipé d'une carte d'acquisition vidéo rapide, d'une carte de commande moteurs et au besoin d'une carte d'acquisition A/D.

La version standard du logiciel permet toutes les opérations de réglage du tensiomètre ( verticalité des différents éléments, calibration des capteurs, paramétrage du traitement d'images, calibration des seringues, etc...), et l'acquisition et le traitement des données à une cadence allant de 5 à 20 images secondes suivant la puissance du micro, l'OS installé et la méthode de traitement.

Un coffret de commande regroupe le contrôleur de température ( contrôleur PID programmable), et les boutons actuateurs pour le système d'injection (boutons "montée" & "descente")