Interfacial rheology: New instrument for analyzing oscillating drops of surfactant solutions

• ACHEMA 2018: KRÜSS presents Drop Shape Analyzer – DSA30R for investigating dynamic interfacial processes for foams and emulsions
• Fast, easy and optimally repeatable measurements with high degree of automation
• Investigation of oscillating drops and gas bubbles in a wide frequency and temperature range

At ACHEMA in Frankfurt (Germany) from June 11 to 15, 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. In practice, such deformations occur whenever multi-phase substance mixtures containing surfactants, such as foams or emulsions, are manufactured, processed or pumped – with different effects on their stability. The DSA30R provides scientific parameters for describing dynamic interfacial processes and optimizing stability behavior. The instrument is of interest in areas such as the food or cosmetics industries as well as enhanced oil recovery.

Interface elasticity and viscosity based on an oscillating drop

The basic measuring principle employed by the DSA30R, the evaluation of an image of a drop or bubble at a needle, 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 interface area 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.

Fast and simple measurements with high reproducibility

In the past, due to laborious test procedures with correspondingly low sample throughput, interfacial rheology has not been used in research and development to a great extent in spite of its informative results. This is now set to change with several simplifications to the DSA30R ranging from preparation and measurement right through to evaluation. 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, from dispensing the drop through the defined oscillation of the volume to outputting the resulting parameters, is controlled by an easily created automation program in the ADVANCE software. Optimal reproducibility and results, which are independent of the user, are ensured by the removal of many manual steps and the accurate specification of all dosing and oscillation parameters.

Analysis of various two-phase systems in a large frequency and temperature range

The DSA30R enables drops to be analyzed in air for SFT-based measurements, or in a bulk liquid for IFT-related results. 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. The large frequency range of 0.001 to 20 Hz for the drop oscillation enables the analysis 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. The ADVANCE software for the DSA30R reads data from the precision sensor and documents the temperature characteristic throughout the whole of the measurement.

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. KRÜSS will be presenting the DSA30R with the ADVANCE software at ACHEMA in Booth D77 in Hall 4.1 along with other new products in the field of interfacial chemistry.