Instrument and methods for surface dilatational rheology measurements

Abstract

We describe an instrument combining the advantages of two methods, axisymmetric drop shape analysis for well-deformed drops and capillary pressure tensiometry for spherical drops, both used for measuring the interfacial tension and interfacial rheological parameters. The rheological parameters are the complex interfacial elasticity, and the surface elasticity and viscosity of Kelvin-Voigt and Maxwell rheological models. The instrument is applicable for investigation of the effect of different types of surfactants (nonionic, ionic, proteins, and polymers) on the interfacial rheological properties both of air/water and oil/water interfaces, and of interfaces between liquids with equal mass densities. A piezodriven system and a specially designed interface unit, implemented in the instrument, ensure precise control for standard periodic waveforms of surface deformation (sine, square, triangle, and sawtooth) at a fixed frequency, or produce surface deformation at constant rate. The interface unit ensures accurate synchronization between the pressure measurement and the surface control, which is used for real-time data processing and feedback control of drop area in some of the applications.

Interfacial rheology: An overview of measuring techniques and its role in dispersions and electrospinning

“…CPT is a versatile technique utilised by a variety of methods for investigating dynamic and equilibrium systems at liquid-liquid and gas-liquid interfaces. This technique is also the only dilatational rheological method that can be used for two liquids with a small density difference (28,29). The principle is based on direct measurement of the pressure difference between two phases separated by the spherical interface of a drop/bubble (15).…”

The role of surfactant type and bubble surface mobility in foam rheology

“…22,[71][72][73][74] In these methods, the surface of the surfactant solution is sinusoidally perturbed, a(t) ¼ a 0 sin(ut), where a(t) ¼ [A(t) À A 0 ]/A 0 is the normalized change of the surface area around the mean area, A 0 , while a 0 is the relative amplitude of oscillations. The resulting variation of the surface tension is measured and (for small deformations) is presented as:…”

The study of the foaming ability of some surfactants

“…The ability to absorption at the interphase boundary and aggregation in the bulk solution is significant for each surfactant [6,7]. Adsorbing at interfaces and forming micelles the surfactants contribute to dissolution, emulsification, foaming and some other processes that occur in solutions [4].Along with the surface activity of the surfactant itself, the foaming ability of a surfactant is characterized by the mechanical strength and viscosity of the films formed [2,4,6].Methods for determining the ability of the foaming ability can be divided into static and dynamic although this division is rather conventional; and taking into account the equipment used in the studies in some cases there is no difference between these methods [5,6]. Determination by dynamic methods is carried out under continuous mechanical action on the solution to prevent the possibility of running off the foam from it [3,5].…”

“…Methods for determining the ability of the foaming ability can be divided into static and dynamic although this division is rather conventional; and taking into account the equipment used in the studies in some cases there is no difference between these methods [5,6]. Determination by dynamic methods is carried out under continuous mechanical action on the solution to prevent the possibility of running off the foam from it [3,5].…”

“…Determination by dynamic methods is carried out under continuous mechanical action on the solution to prevent the possibility of running off the foam from it [3,5]. Under dynamic conditions the volume of the foam measured is determined by the ratio between the rate of its formation and its destruction, and the volume of foam under static conditions is dependent on the speed of bubbles dissolution.…”