Dynamic interfacial tensiometry

Edited by T. Kajiyama and M. Aizawa Vol. 5 Foam and Foam Films. By D. Exerowa and P.M. Kruglyakov Vol. 6 Drops and Bubbles in Interfacial Research. Edited by D. Mobius and R. Miller Vol. 7 Proteins at Liquid Interfaces. Edited by D. Mobius and R. Miller Vol. 8 Dynamic Surface Tensiometry in Medicine. By V.M. Kazakov, O.V. Sinyachenko,... 

The general application of tensiometry was shown in [241] and it was impressively demonstrated how large the capacity of interfacial studies for medical research is. For example, selected dynamic surface tension values of serum or urine correlate with the health state of patients suffering from various diseases. In the course of a medical treatment these values then change from a pathological level back to the normal values determined as standard for a certain group of people (age and sex). 

Drop and bubble shape tensiometry is a modem and very effective tool for measuring dynamic and static interfacial tensions. An automatic instrument with an accurate computer controlled dosing system is discussed in detail. Due to an active control loop experiments under various conditions can be performed constant drop/bubble volume, surface area, or height, trapezoidal, ramp type, step type and sinusoidal area changes. The theoretical basis of the method, the fitting procedure to the Gauss-Laplace equation and the key procedures for calibration of the instrument are analysed and described. 

We will consider first the dynamical rheological properties of concentrated inverse emulsions (stabilized by Span 80 in dodecane) for various volume fractions ( ). The experimental results are given in the form of the plot G Rd/( in relation to ( ) (Figure 2.8, hollow symbols). From the value of the interfacial tension, y = 3.5mN-m measured by tensiometry, and using 3, we calculate values for a and ( )c equal to 1 and 0.66, respectively. We will therefore use this measured value of a in the subsequent analysis of concentrated multiple emulsions. 

There are various direct measurements of micellar solutions giving access to the dynamics rate constants - mainly based on disturbance of the equilibrium state by imposing various types of perturbations, such as stop flow, ultrasound, temperature and pressure jump [14,15[. This aspect is also not further elaborated here we focus instead on the impact of micellar kinetics on interfacial properties, to demonstrate that tensiometry and dilational rheology are suitable methods to probe the impact of micellar dynamics. The first work on this subject was published by Lucassen already in 1975 [16[ and he showed that the presence of micelles in the bulk have a measurable impact on the adsorption kinetics, and hence on the dilational elasticity, when measured by a longitudinal wave damping technique. Subsequent work demonstrated the effect of micellar dynamics on non-equilibrium interfacial properties [17-29]. The physical idea of the impact of micellar dynamics on the dynamic properties of interfacial layers can be easily understood from the scheme given in Figure 13.1. 

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