Impact of irreversibly adsorbed surfactant layers at fluid-fluid interfaces on coalescence
Lynn Walker (Carnegie Mellon University), Matthew Reichert (Carnegie Mellon Univ.), Shelley Anna (Carnegie Mellon Univ.)
Complex Fluids: Suspensions, Emulsions, and Gels
Tue 4:20 - 5:40
Barus-Holley 160
The dynamics of adsorption of single and multicomponent surfactant mixtures at oil-water and air-water interfaces has been characterized using a microtensiometer. The use of microscale interfaces allows the transport processes involved in adsorption to be analyzed and both diffusion and kinetic parameters characterized. The scale of the device allows the bulk solution in contact with the interface to be changed rapidly. We are able to remove the bulk surfactant at different points in during the dynamics of adsorption by rinsing the interface and continuously replacing the bulk fluid with surfactant-free aqueous phase to investigate the reversibility of adsorption. For a bulky nonionic surfactant, Tween-80, a critical interfacial tension arises that links the transport dynamics to the onset of partial reversibility in the system. By measuring the mechanical properties of pre-rinsed and rinsed interfaces, we also find a critical interfacial tension that leads changes in the elasticity of the interfaces. This interfacial tension correlates well with the critical interfacial tension that indicates the onset of partial reversibility. To determine the effects of interfacial elasticity and concentration changes on the stability of an emulsion, we bring two surfactant-coated interfaces into contact and monitor coalescence times and initial droplet shape profiles. We discuss these coalescence results in the context of film drainage, and as drainage time relates to the elasticity of the contacted interfaces. The addition of other surface active species, AOT and rhamnolipid, is also characterized to determine the impact of these surfactants on the reversibility of Tween-80 and on the elasticity of the resulting mixed interfaces.