Effect of polyelectrolyte–surfactant complexation on Marangoni transport at a liquid–liquid interface Gunnar Dunér a,b , Michelle Kim a,b , Robert D. Tilton a,b,c,⇑ , Stephen Garoff a,d , Todd M. Przybycien a,b,c a Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States b Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States c Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States d Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, United States highlights  Polymer complexation alters surfactant-induced Marangoni flow at oil/water interface.  Polymer adsorption irreversibility creates hysteresis in adsorption/rinse cycles.  Polymers alter extent and direction of net displacement vs. surfactant-only system. graphical abstract article info Article history: Received 3 November 2015 Revised 6 January 2016 Accepted 6 January 2016 Available online 7 January 2016 Keywords: Marangoni convection Particle transport Interfacial tension gradient Cationic polymer Surfactant Polymer/surfactant complexation abstract Complexation of surfactants and oppositely charged polyelectrolytes is expected to alter Marangoni transport at a fluid interface compared to either single component system due to altered interfacial ten- sion isotherms and mass transfer rates as well as adsorption irreversibility effects. We investigate Marangoni transport at the oil/water interface by passing mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and cationic polyelectrolyte poly(3-(2-methylpropionamide)propyl) trimethylam- monium chloride-acrylamide (poly[AM-MAPTAC]), or rinsing solutions, over an oil/water interface in a radial, stagnation point flow. The displacements of adsorbed tracer particles are recorded through optical microscopy. The net displacement, defined as the sum of the displacements occurring during the adsorp- tion and desorption stages of one application and rinsing cycle, is up to 10 times greater for complexing surfactant/polymer mixtures compared to either single component system. The enhanced net displace- ment is largely determined by the enhanced transport upon adsorption, while the reverse displacement that would normally occur upon rinsing is partially suppressed by partially irreversible polymer adsorp- tion at the oil/water interface. In addition to effects of complexation on interfacial tension gradient induced flow, complexation effects on the bulk, and possibly interfacial, viscosity also influence the inter- facial transport. Ó 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2016.01.011 0021-9797/Ó 2016 Elsevier Inc. All rights reserved. Abbreviations: SDS, sodium dodecyl sulfate; poly(AM-MAPTAC), poly([3-(2-methylpropionamide)propyl] trimethylammonium chloride-acrylamide); CTAB, hexade- cyltrimethyl ammonium bromide; PMMA, poly(methylmethacrylate). ⇑ Corresponding author at: Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States. E-mail address: tilton@cmu.edu (R.D. Tilton). Journal of Colloid and Interface Science 467 (2016) 105–114 Contents lists available at ScienceDirect Journal of Colloid and Interface Science journal homepage: www.elsevier.com/locate/jcis