Paper Number
SF2 

Session
Surfactants, Foams and Emulsions

Title
The stability and coalescence of water in oil emulsions: Temperature and salinity effects

Presentation Date and Time
October 10, 2022 (Monday) 4:05

Track / Room
Track 7 / Ontario

Authors (Click on name to view author profile)

  1. Bachnak, Rana B. (University of Minnesota - Twin Cities, Mechanical Engineering)
  2. Moravec, Davis B. (Donaldson Company)
  3. Hauser, Brad G. (Donaldson Company)
  4. Dallas, Andrew J. (Donaldson Company)
  5. Dutcher, Cari S. (University of Minnesota - Twin Cities, Mechanical Engineering & Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Rana B. Bachnak1, Davis B. Moravec2, Brad G. Hauser2, Andrew J. Dallas2 and Cari S. Dutcher3
1Mechanical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN 55455; 2Donaldson Company, Bloomington, MN 55431; 3Mechanical Engineering & Chemical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN 55431

Speaker / Presenter 
Bachnak, Rana B.

Keywords
experimental methods; theoretical methods; emulsions; surfactants

Text of Abstract
The dynamics at the liquid-liquid interface for surfactant-stabilized systems is important for different applications, such as liquid-liquid separations and treatment strategies. The interfacial properties are affected by several factors, such as the temperature of the system and the salinity of the emulsion. The first factor studied here is the temperature. In industrial applications, oil-water emulsions are subject to a wide range of temperatures, known to affect the interfacial tension (IFT), as well as the bulk and inner phase viscosity. In this work, the effect of temperature on IFT is studied by means of a microfluidic device mounted on a cold stage, used to access sub-ambient temperatures. The microfluidic device measures IFT using a contraction-expansion mechanism. Measurements are done for water emulsions in light mineral oil, with different SPAN 80 surfactant concentrations in the oil phase. It was found that the IFT increases at sub-ambient temperatures, compared to ambient temperatures. In addition to that, the dynamics of surfactant transport is studied by fitting an equation of state based on Langmuir isotherm to the dynamic IFT measurements to extract the adsorption rates of surfactant. It was shown that at sub-ambient temperature, early time variation in IFT can be resolved, contrary to ambient temperature at which only late time results were resolved, suggesting slower transport at sub-ambient temperature. The second factor studied is the salinity of water droplets in oil. The IFT of salt water in model oil with different SPAN80 concentrations is measured using pendant drop experiments. It was found that the presence of salt decreases the IFT, suggesting a more stable droplet. The stability of those droplets is also studied by measuring their ability to coalesce, using a microfluidic device that allows the measurement of the film drainage time, which is the time taken for the droplets to coalesce. It is suggested that the salt will increase the film drainage times of water droplets in oil.