These flow properties are important for many products and industries since they determine the behavior and stability of suspensions, emulsions, froth and foams. For example, paints, pharmaceuticals, cosmetics, personal care and food products all require optimum composition and stability for their performance and shelf life. The petrochemical and mineral processing industries often struggle with problems associated with emulsion and froth stability.
Surfactants, polymers, lipids, proteins or particles can influence the flow and stability properties of liquid interfaces in a formulation. Dilatational interfacial rheological parameters can be determined by changing the area of the interface, and measuring the change in interfacial tension by drop shape analysis. The Theta pulsating drop offers a powerful combination for studying flow behavior and determining interfacial rheological parameters of liquid interfaces.
When surface-active molecules are present in a liquid, they tend to adsorb in the liquid-vapor and/or liquid-liquid interface as illustrated in Figure 1. Interfacial rheology deals with the response of the adsorbed interfacial layer on the deformation. The response depends on the layer composition, and thus interfacial rheology is relevant in many applications in which adsorbed layer play a crucial role, for example in development surfactants, foams and emulsions.
Figure 1: Adsorbed molecular layers in liquid-vapor and liquid-liquid interfaces
Figure 2A: In dilatational interfacial rheology, deformation to the adsorbed molecular layer is caused by dilation/compression of the droplet.
Figure 2B: Interfacial tension (grey circles) follows the change in droplet area (turquoise squares).
Attension® Theta combined with pulsating droplet module, PD-200, enables dilatational interfacial measurements, where interfacial tension and droplet area changes are recorded as a function of time and frequencies. From this data viscoelastic properties of adsorbed molecular layer are calculated according well established theories1 2 resulting in parameters below:
PD-200 and OneAttension software (Figure 3) offers a practical approach to dilatational interfacial measurements. The software includes automatic multipoint measurement of viscoelastic properties as a function of frequency and time. A unique volume-from-image function in OneAttension can compensate for droplet evaporation and real-time analysis enables pre-testing of suitable frequency levels and experimental follow-up. PD-200 has great solvent resistance and can be installed in few minutes.
Figure 3: Pulsating droplet volume experiment with the OneAttension Software live analysis.
To read a real-life example of how dilatational interfacial rheology measurements have been utilized, click to the case study below.