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A surfactant is a chemical compound that adsorbs onto a fluid-fluid interface and reduces its surface tension. A non-uniform distribution of such compounds at the interface causes a Marangoni stress that drives a flow, which in turn transports the surfactant. Estimating in situ the degree to which the adsorbed surfactant is out of equilibrium with the dissolved state is critical but challenging, especially because of the multiple length- and time-scales the surfactant and fluid dynamics span. In this presentation, I show that combining asymptotic analysis of the governing mathematical model with experimental flow visualization and velocimetry can furnish a near-complete description of the dynamics.
An epitome of such a system is the axisymmetric flow driven by a steady point source of surfactant on the surface of a deep liquid pool. In this case, the state of the surfactant is difficult to gauge, without which even simple order-of-magnitude scaling theories remain incomplete. I show that by examining three invariant characteristics of the flow, and without knowledge of the surfactant physicochemical parameters, the nature of the surfactant dynamics can be deduced.

The Royal Society invites applications for the Dorothy Hodgkin fellowships. These enable early-career scientists who require a flexible working pattern due to personal circumstance to take the first step into an independent research career. Research may address all areas of the life and physical sciences, including engineering, but excluding clinical medicine, social sciences and humanities.

Applicants must have completed their PhD but have no more than six years of research experience after receipt of their PhD award. Individuals who hold a permanent post in a university or non-profit organisation may not apply. Preference may be given to applications from underrepresented groups. Applicants can be of any nationality but the fellowship must be held at a UK university or not-for-profit research organisation.

Approximately six to eight awards are available for five years. Funding covers 80 per cent of the basic salary costs up to 拢40,681 in the first year, estates costs and indirect costs; as well as research expenses worth up to 拢13,000 for the first year and up to 拢11,000 annually thereafter.

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