Marangoni Flow in Freely Suspended Liquid Films

Area of Science:

• Physics
• Materials Science
• Fluid Dynamics

Background:

• Thin freely suspended smectic films exhibit complex behaviors under thermal gradients.
• Marangoni effects, driven by surface tension gradients, are known to influence fluid flow.
• Understanding material transport in microgravity is crucial for advanced material processing.

Purpose of the Study:

• To demonstrate and quantify controlled material transport in thin smectic films driven by temperature differences.
• To investigate the role of Marangoni effects in directing material flow within these films.
• To develop and validate a model predicting material transport behavior.

Main Methods:

• Experiments were conducted on submicrometer thick smectic films with millimeter lateral extensions.
• Studies were performed in microgravity conditions during suborbital rocket flights.
• In-plane temperature differences were applied to induce Marangoni effects, and material accumulation was observed.

Main Results:

• Directed material transport was observed, with flow direction dependent on the surface tension's temperature coefficient (dσ/dT).
• Materials with dσ/dT<0 showed transport from hot to cold edges, accumulating at the cold edge.
• Materials with dσ/dT>0 exhibited reverse transport from cold to hot edges.
• A quantitative model was developed, highlighting the relevance of the temperature difference between thermopads over the in-plane gradient.

Conclusions:

• Temperature differences effectively control material transport in thin smectic films via Marangoni effects.
• The direction of transport is predictable based on the material's surface tension temperature coefficient.
• The developed model accurately describes the observed phenomena and identifies key driving parameters.