English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

For an immiscible oil drop immersed in a stably stratified ethanol-watermixture, a downwards solutal Marangoni flow is generated on the surface of thedrop, owing to the concentration gradient, and the resulting propulsioncompetes against the downwards gravitational acceleration of the heavy drop. Inprior work of Li et al. (Phys. Rev. Lett., vol. 126, issue 12, 2021, 124502),we found that for drops of low viscosity, an oscillatory instability of theMarangoni flow is triggered once the Marangoni advection is too strong fordiffusion to restore the stratified concentration field around the drop. Herewe experimentally explore the parameter space of the concentration gradient anddrop radius for large oil viscosities and find a different and new mechanismfor triggering the oscillatory instability in which diffusion is no longer thelimiting factor. For such drops of higher viscosities, the instability istriggered when the gravitational effect is too strong so that the viscousstress cannot maintain a stable Marangoni flow. This leads to a critical dropradius above which the equilibrium is always unstable. Subsequently, a unifyingscaling theory that includes both the mechanisms for low and for highviscosities of the oil drops is developed. The transition between the twomechanisms is found to be controlled by two length scales: The drop radius $R$and the boundary layer thickness $\delta$ of the Marangoni flow around thedrop. The instability is dominated by diffusion for $\delta<R$ and by viscosityfor $R<\delta$. The experimental results for various drops of differentviscosities can well be described with this unifying scaling theory. Ourtheoretical description thus provides a unifying view of physicochemicalhydrodynamic problems in which the Marangoni stress is competing with a stablestratification.

Marangoni instabilities of drops of different viscosities in stratified liquids