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Abstract

This thesis comprises three parts. In the first part, we study the formation of topological
defects surrounding colloidal particles of various geometries immersed in liquid crystals.
The impact of extreme geometry, such as a fractal, on the number of topological defects
formed around the particles is studied. We print hollow prisms with fractal base of several
iterations to study this effect. As we increase the fractal iteration, we observe the creation
of additional topological defect pairs whiles conserving the total topological charge.
Experimental observations and numerical simulations reveal a geometry-based scaling law
connecting the number of topological defects to the geometry of the particles. Next we
test the impact of chiral environment on the formation of topological defects on particles
with higher genus. We observe the formation of distinct topological states, that become
more complicated with increasing chirality compared to the particle size. We use several
polarization optical microscopy methods to study the structures.
In the second part, we study the thermal properties of thin nematic layers as they are
undergoing rapid phase transition. For this purpose we develop an experimental technique
allowing us to measure the time dependency of the temperature inside the liquid crystalline
sample cell with the liquid crystal medium acting as a fast thermometer. After laser heating
we measure the temperature time dependency to determine the speed of the cooling at
the phase transition. By comparing experimental observations and extensive computer
simulations of the thermal properties of our system we are able to report cooling rates of
up to 40 000K=s, which allow the sample to cool from the initial temperature of above
100 °C to the nematic phase in approximately 1 ms.
In the third part, we develop and use a nanosecond incoherent illumination system
and a stroboscopic imaging technique to study the formation of nematic ordering as the
liquid crystal is rapidly cooled. This allows us to study the process with nanosecond resolution,
which is at least six orders of magnitude faster than previous observations. Due
to the random nature of the isotropic nematic phase transition we study the process by
stroboscopic imaging. We take a single image per experiment and delay the exposition in
between experiments to stitch the images together forming a movie of the process. We use
an sensitive camera equipment to study the emergence of the first nematic ordering from
the isotropic melt. Next we develop a custom image processing algorithm to study the
emergence of light patches on the images, which are a direct consequence of the formation
of nematic ordering from the isotropic melt. We determine the properties and the distributions
of the patches as a function of time after the start of the cooling and the radius
of the heated area. The resulting data allow us to study the predictions of the Kibble-
Zurek mechanism, that describes the formation of nematic domains and its cooling rate
dependency. Furthermore, by using light transmission, we are able to study the coarsening
dynamics in the samples and determine a sample thickness dependency of the coarsening
time. Lastly, we combine the data from the observation of the rapid phase transition with
the temperature measurements to determine the supercooling of the isotropic phase for up
to 500 µs or in terms of temperature up to 10 °C below the phase transition.