Electrical impedance changes and water content in O/W emulsions during evaporation

Abstract

Synopsis A method for measuring the variation of electrical impedance (Z) of thin layers (0.1 mm) of O/W emulsions during evaporation in a controlled environment is presented. The evaporation of an emulsion base (A) either as such and containing 1% glycerin (B) or 1% sodium pyrrolidonecarboxylate (C) was investigated for 120 min at constant air temperature (25 degrees C) and relative humidity (55%). The measured impedance of the emulsion layers increased by three orders of magnitude during the evaporation cycles. The relationship between impedance and water content of the evaporating emulsion layers was investigated. Each emulsion showed a complex linear relationship between log Z and water content, the relationship being represented by two (three, for emulsion A) linear portions in the graph. Plots of water content vs. time, temperature vs. time and rate of water loss vs. water content of the emulsion layers are presented. The data appear to indicate that evaporation proceeds via distinct stages, whose correspondence to different mechanisms of water evaporation is discussed. The potentiality of the present method for water analysis, and for investigating structural changes in emulsions during evaporation, is also discussed.

Geranyl acetate emulsions: Surfactant association structures and emulsion inversion

“…These latter results combined with the early reports of Saettone et al [11], of Friberg et al [12] and of Vathey et al [13] indicated that association structures play a substantial role in the evaporation and prompted investigations into these phenomena utilizing phase diagrams and an algebraic system to extract additional information [14,15]. This research provided information about potential phases that would be encountered during evaporation of emulsions and among other results, the potential to formulate emulsions in which the fragrance evaporates under constant vapor pressure [16] should be mentioned.…”

A comparison between the experimental and estimated evaporation paths from emulsions

“…[5][6][7][8][9] Others have focused on the behaviour of emulsions in the presence of solid surfaces in selected cases, [10] but the only fundamental general investigation in this important area was done by Kapilashrami et al [11] These are all investigations of the highest international standard of the initial process, during which the emulsion retains the two-phase organization, but for application purposes information is equally vital for the later stages in the evaporation process, since the emulsion features at these periods are potentially even more significant for the action of the emulsion. To the best of our knowledge, the only early study providing such information was published by Saettone et al [12] They found that the evaporation rate of an oil/water (O/W) emulsion clearly varied in a number of well-defined ranges during the entire evaporation period.…”

Effect of relative humidity on the evaporation path from a phenethyl alcohol emulsion

“…As a result insight into the conditions during the prolonged evaporation in a number of emulsion applications had not at the time become the focus of research with the exception of an early contribution by Saettone et al [22], who found the electric impedance versus the water content of an O/W emulsion to attain distinctly different values in a number of discrete ranges during the extended process. This find indicated evaporation to induce structural changes in the emulsion and led Friberg et al [23] to attempt a new approach to gain more detailed information concerning such changes during the process.…”