Dynamic surface tension measurements with submillisecond resolution using a capillary-jet instability technique.

Area of Science:

• Physical Chemistry
• Surface Science
• Fluid Dynamics

Background:

• Surface tension is a critical property of liquids, influenced by surfactant adsorption dynamics.
• Measuring dynamic surface tension, especially at short timescales, is crucial for understanding interfacial phenomena.
• Existing methods often face limitations in resolving rapid changes in surface tension.

Purpose of the Study:

• To implement and validate an oscillating capillary jet method for measuring dynamic surface tension.
• To investigate the dynamic surface tension of aqueous Tergitol NP-8 surfactant solutions.
• To determine the influence of surface age and surfactant concentration on dynamic surface tension.

Main Methods:

• Utilized an oscillating capillary jet method to continuously capture jet evolution.
• Employed a linear, axisymmetric, constant-property model for surface tension determination.
• Validated the method with deionized water and isopropyl alcohol, establishing an optimum wavelength procedure.
• Performed measurements on concentrated aqueous Tergitol NP-8 solutions over a 0.6-4.2 ms time window.

Main Results:

• The oscillating capillary jet method successfully measured dynamic surface tension as a function of surface age.
• Dynamic surface tension data for Tergitol NP-8 solutions, including submillisecond ages, were obtained.
• The Hua and Rosen correlation accurately described the experimental dynamic surface tension data.
• Increased surfactant concentration enhanced jet stability, enabling measurements at higher surface ages.

Conclusions:

• The oscillating capillary jet method is a reliable technique for measuring dynamic surface tension at short timescales.
• The study provides valuable dynamic surface tension data for nonionic surfactant solutions.
• Adsorption kinetics theory was used to estimate the time for surface tension to reach equilibrium.