Dynamic interfacial properties of drops relevant to W/O-emulsion-forming systems: A refined measurement apparatus

Detailed construction is presented for a refined instrument designed for the accurate measurement of dynamic interfacial tension, both in the frequency domain and in the time domain, in liquid/gas and in liquid/liquid systems. The instrument is an integrated combination of a profile-analysis tensiometer with a capillary-pressure tensiometer. The measurement process is firmly established on the independent acquisition in synchronism of two sets of observable physical properties (namely, the drop-profile coordinates and the differential pressure). The favourable comparison of the determined interfacial tension from the two data sets, in an overlapping range of experiment parameters, grants reliability of the measurement values. The requirements of the scientific metrology and the foundation principles of the measurement theory are included in the instrument presentation. Novel software features, for the instrument operation and for the subsequent data processing, characterise the described apparatus, as a distinct variant of similar tensiometers, based on axisymmetric liquid menisci methods. The example results show different measurement applications to water/model-hydrocarbon systems, illustrating the principal performances. The potentiality of the described instrumentation, in addition to the determination of the steady-state linear interfacial viscoelasticity, extends towards a quantitative assessment for the transient non-linear interfacial processes, which are essential phenomena inherent in drop-drop interactions. (c) 2007 Elsevier B.V. All rights reserved.