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|Surface Dilatational Elasticity and Oscillation - Part Two|
Last month we discussed how the axisymmetric bubble shape method has
proven useful in the measurement of surface dilatational elasticities
and viscosities. We also introduced our new Oscillator hardware, p/n
100-28, which is specifically designed for studying surface dilatational
rheology through periodic oscillatory deformation. This month we present
the video below which shows
a simple experiment with two different frequencies. If you cannot view
it from this email, simply
click here or go to our website
www.ramehart.com and click on Oscillator.
Japanese researchers1 have recently studied the surface dilatational elasticity properties of polyglycerol fatty acid esters, namely whey protein and sodium caseinate in aqueous systems. These compounds, in addition to being consumed in milk (they help improve product stability) and bodybuilding supplements, are used in the production of adhesives, binders, and additives, and due to their excellent gelling and emulsification properties they are used in a wide spectrum of food products. The referenced researchers have learned that surface dilatational elasticity contributes to the foamability of aqueous systems of fatty acid ester type surfactants.
In a related study, Wang and Narsimhan2 at Purdue University studied the interfacial dilatational rheological properties of β-Lactoglobulin at the air-water interface. β-Lactoglobulin is also a whey protein of cow's milk. Oddly enough it's not found in human milk. Some researchers believe that its primary role is that of a transport mechanism. But one of the reasons it's studied so frequently may be in part due to its abundance and the ease of purifying. It holds the interest of food researchers since it plays a critical role in dairy products and processing.
In the Purdue study, a model was developed using a pulsating bubble tensiometer at various frequencies and at elevated temperatures. Their method could easily be tested using the ramé-hart Oscillator and Environmental Chamber. They conclude that their method using oscillatory deformation more correctly reports interfacial dilatational elasticity. But viscosity values tends to fall in line with traditional methods. A number of other recent studies3,4 explore the impact of surface and mechanical properties and rheology of β-Lactoglobulin-stabilized emulsions.
Researchers at the University of Berlin5 and others6 have studied the surface dilatational behavior of the surfactant protein B (SP-B) and variants at relatively low frequencies (0.04 to 0.2 Hz). This work contributes to the solutions for pulmonary surfactant protein B deficiency, a rare lung condition that results in respiratory problems. A number of commercially available lung surfactants (such as Alveofact and Curosurf) aim to reduce surface tension which in turn make it easier to breathe and reduces fluid accumulation. The Berlin study shows how these pulmonary surfactant components can reduce the effort required for respiration and thus improve the condition of patients with infant respiratory distress syndrome and other respiratory and pulmonary conditions (such as pulmonary alveolar proteinosis).
Boundless other studies have used sinusoidal oscillation and step relaxation techniques to measure surface dilatational elasticities and viscosities with the axisymmetric bubble shape method.7-9
1 Journal of Oleo Science, 2008, 57 (9), pp
We would like to wish you a Happy Holiday from all of us at ramé-hart instrument co. Thank you for helping make 2008 a good year despite the economic woes that beset all of us. We wish you a safe and festive holiday season as well as a Happy New Year 2009.