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On some nanoscopic aspects of capillarity
Inside the field of condensed matter physics, capillarity has the particularity to involve three otherwise separated domains : macroscopic thermodynamics, fluid mechanics and statistical physics. In the first part
of the seminar, I will address a number of conceptual questions that are often encountered when discussing capillarity. Why is surface tension a force parallel to the interface while it is so obvious that it must be perpendicular to it ? What is the system on which the forces that we draw in the Young’s construction are applied ? What is the force exerted by a liquid on an elastic solid below a contact line ? Are surface tension and adhesion work identical ? Is there a stress anisotropy close to the interface of an elastic solid ? Ad lib. I will provide a perspective on capillarity that reconciles the macroscopic viewpoints, from
thermodynamics or fluid mechanics, and the microscopic perspective from statistical physics.
In the second part of the seminar, I will present molecular dynamics simulations of Lennard-Jones nanodrops, that allow to discuss the existence and origin of line tension. I will show that the deviation from
Young’s law is very small and would correspond to a typical line tension length scale (defined as line tension divided by surface tension) similar to the molecular size and decreasing with Young’s angle. I will propose an alternative interpretation based on the geometry of the interface at the molecular scale.
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