Drop Size Dependence of the Apparent Surface Tension of Aqueous Solutions in Hexane Vapor as Studied by Drop Profile Analysis Tensiometry

• Main Authors: Valentin B. Fainerman, Volodymyr I. Kovalchuk, Eugene V. Aksenenko, Altynay A. Sharipova, Libero Liggieri, Aliyar Javadi, Alexander V. Makievski, Mykola V. Nikolenko, Saule B. Aidarova, Reinhard Miller
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Colloids and Interfaces
• Subjects: drop profile analysis tensiometry; solution–alkane vapor interface; dynamic apparent surface tension; non-ionic surfactant; thermodynamic model
• Online Access: https://www.mdpi.com/2504-5377/4/3/29

Surface tension experiments were performed using the drop profile analysis tensiometry method. The hexane was injected into the measuring cell at certain times before the formation of the solution drop. The influence of the capillary diameter and solution drop size on the measured apparent dynamic surface tension was studied. The amount of hexane transferred from the vapor phase to the drop was estimated. For large pure water drops, it was shown that the ageing of the drop in the hexane vapor during a long time resulted in the formation of a liquid hexane phase covering the drop, but the volume of this phase did not exceed 0.5 mm³. On the contrary, for surfactant solution drops the volume of the hexane phase covering the drop was essentially larger. Experiments with solution drops were performed to measure the surface tension within a wide range of surfactant concentration. It was found that the dependencies of dynamic surface tension on the C₁₃DMPO and C₁₄EO₈ solutions concentration exhibit maxima at concentrations of about 1–2 μmol/L for C₁₄EO₈ and 2–5 μmol/L for C₁₃DMPO at ageing times of 100 to 1000 s; these maxima were shown to exist also at equilibrium. This phenomenon is presumably ascribed to the competitive character of simultaneous adsorption of hexane and surfactant.