טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLeizerson Ilya
SubjectPattern Formation in Wetting-Dewetting Phenomena
DepartmentDepartment of Physics
Supervisor Professor Emeritus Stephen Lipson


Abstract

In this research we studied the behavior of a volatile water film on a mica surface. Under saturated vapor pressure, a mica surface is completely wetted by water. As this water evaporates, it breaks up into patterns of two characteristic thicknesses: a molecularly thin and a macroscopically thick film.

 We developed a novel imaging technique for measuring of thin film thickness on transparent substrates. The sensitivity is found to be equal to 5Å. This achievement enabled to confirm experimentally the coexistence of a thin (<30Å) water film with a much thicker one during the evaporation and to measure their thicknesses.

In study of kinetics of an evaporating film on a solid substrate, we found experimentally, in contradiction to accepted thesis, that material diffusion via gas phase is considerably faster than hydrodynamic film flow.

Another phenomenon that we investigated was behavior of an ensemble of volatile liquid drops. In general, large drops grow at the expense of smaller ones. However, an array of variously sized water drops on mica behaves differently; below the equilibrium vapor pressure, the largest drops evaporate fastest. We give a complete explanation showing that this behavior is related to thick and thin water films coexisting during evaporation.

A behavior different from Rayleigh instability was revealed in the moving front of a water film on a mica substrate. Surface tension effects alone can not give an explanation for a simultaneous reduction of the curvature-radius of the rim and an increasing mean distance between fingers. We demonstrate that the long-range forces between the liquid and the substrate are responsible for this behavior.