New Instrument for Analysing Oscillating Drops of Surfactant Solutions

At Achema 2018, Krüss will be presenting a newly developed measuring instrument for interfacial rheology, the Drop Shape Analyzer - DSA30R. The unit measures the change in surface or interfacial tension (SFT/IFT) during deformation of the phase boundary. The DSA30R provides scientific parameters for describing dynamic interfacial processes and optimising stability behaviour.

The basic measuring principle employed by the DSA30R, the evaluation of an image of a drop suspended from a needle (Pendant Drop), is an elegant method for measuring IFT/SFT which has long been used by Krüss. The essential capacity of the instrument consists in periodical and exactly sinusoidal variation of the drop surface by extremely precise control of the dosing feed. The IFT/SFT is measured as a function of the surface change, and likewise varies sinusoidally in the case of samples containing surfactants. The modulus of elasticity E’ and the modulus of viscosity E” are obtained from the evaluation. E’ goes hand-in-hand with the change in surface concentration of the surfactant due to stretching and compression; E” reflects the change in IFT/SFT with respect to time due to diffusion and interfacial adsorption of the dissolved surfactant.

The sample is placed in a commercially available glass syringe, which is inserted in just a few simple steps and fully automatically coupled to the dosing feed. Air bubbles in the dosing system, which were a frequent source of errors in interfacial rheology of the past, can be easily avoided with the DSA30R. The whole measuring procedure is controlled by an easily created automation program in the Krüss’s ADVANCE software.

The DSA30R enables drops to be analysed in air for measuring the SFT, or in a bulk liquid for the IFT. The drop can also be investigated rising in a heavy phase in order to investigate crude oil or asphaltene solutions in an aqueous environment, for example. of extremely slow to very fast interfacial processes.

In order to investigate the effect of temperature or to simplify measurements in systems with higher viscosity, the syringe is embedded in a temperature-controlled jacket for measurements up to 70°C, wherein the temperature of the bulk phase can also be controlled.

As an alternative to the DSA30R as a pre-configured measuring instrument, the Oscillating Drop Module – ODM for interfacial rheology is also available as an accessory for extending the functional scope of existing Krüss measuring systems.