title: Transient Marangoni transport of colloidal particles at the liquid/liquid interface caused by surfactant convective-diffusion under radial flow.
abstract: OBJECTIVE
  Interfacial tension gradients at a liquid/liquid interface drive Marangoni flows. When colloidal particles are adsorbed to an interface in systems with spatial and temporal gradients of surfactant concentration, these interfacial flows can be potentially significant contributors to the direction and rate of particle transport.
  
  
  METHODS
  In this work, we use optical microscopy to measure the interfacial velocities of 5μm diameter polystyrene latex particles adsorbed at an oil/water interface, using olive oil to represent polar oils often encountered in cleaning applications.
  
  
  RESULTS
  On surfactant adsorption the maximum interfacial velocity scales linearly with bulk surfactant concentration, even for concentrations exceeding the critical micelle concentration (CMC). The maximum interfacial velocity weakly decreases with increasing flow rate, but it varies non-monotonically with the radial distance from the inlet. Upon surfactant desorption into a rinse solution, the maximum velocity increases with increasing concentration of the original surfactant solution, but only up to a plateau near the CMC. These experimental trends are well-described by a convective-diffusion model for surfactant transport to or from the liquid/liquid interface coupled with Langmuir-type adsorption, using a constitutive relation between the interfacial tension gradient and interfacial velocity based on the interfacial tangential stress jump.
authors.affiliation: Center for Complex Fluids Engineering and Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Dunér
authors.affiliation: Center for Complex Fluids Engineering and Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Stephen
authors.initials: S
authors.lastname: Garoff
authors.affiliation: Center for Complex Fluids Engineering and Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States; Center for Complex Fluids Engineering and Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Todd M
authors.initials: TM
authors.lastname: Przybycien
authors.affiliation: Center for Complex Fluids Engineering and Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States; Center for Complex Fluids Engineering and Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States. Electronic address: tilton@andrew.cmu.edu.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Tilton
keywords: Interfacial tension gradient; Marangoni stress; Radial flow cell; Stagnation point flow; Surfactant adsorption/desorption