Monolayers of amphiphilic molecules at the air/water interface, Langmuir
monolayers, provide an experimentally accessible system for the study of
physics in two dimensions. As a function of temperature and density,
Langmuir monolayers display a series of phases and phase transitions; this
thesis describes several optical experiments which clarify the macroscopic
properties of some of these monolayer phases.
In one experiment a combination of two techniques, laser light scattering
and Brewster angle microscopy, is used to study the effect of inhomogeneous
monolayers on the damping of capillary waves. It is shown that the monolayer
contributes to the capillary wave damping when the size of a typical
monolayer domain is equal to or larger than the capillary wavelength.
Secondly, a new technique to measure the tilt angle of molecules from
the surface normal is described. The validity of the technique is demonstrated
by comparison to previously performed x-ray scattering experiments. The tilt
angle of a monolayer of long-chain alcohol molecules is measured as a
function of temperature and pressure near first- and second-order phase
transitions from tilted to untilted monolayer phases.
Finally, depolarized Brewster angle microscopy is used to study
orientational fluctuations in a two-dimensional smectic-C liquid crystal. The
results are in excellent agreement with theoretical predictions. In addition,
the first measurements of orientational elasticity and viscosity in a liquid
crystal system with variable density are presented.
Research area description 
