Dilatational yielding of solid Langmuir monolayers

Area of Science:

• Materials Science
• Surface Chemistry
• Physics

Background:

• Previous work by Muruganathan and Fischer demonstrated laser-induced local collapse of methyl stearate monolayers.
• Laser intensity control allows for a highly controlled study of monolayer collapse mechanisms.

Purpose of the Study:

• To extend previous findings by investigating local yielding as an alternative pathway to monolayer collapse.
• To determine the threshold laser power for local yielding to dominate over global collapse.
• To analyze the role of temperature and pressure gradients in laser-induced monolayer collapse.

Main Methods:

• Corroboration of the thermocapillary nature of laser-induced collapse.
• Determination of the threshold laser power for the local yielding pathway.
• Analysis of temperature and pressure gradients at the laser focus.

Main Results:

• Laser-induced collapse is confirmed as a thermocapillary effect.
• The threshold laser power is primarily governed by temperature and pressure gradients, not global values.
• Local yielding occurs when the monolayer's yield stress is exceeded, creating a material sink at the laser focus.

Conclusions:

• Local yielding presents a distinct pathway for monolayer collapse, competing with global collapse.
• The study provides estimates for the dilatational yield pressure of the solid methyl stearate monolayer.
• Understanding these collapse mechanisms is crucial for applications involving thin films and surface phenomena.