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Abstract:
The doctoral thesis presented here is one of the first systematic attempts to unravel the
wonderful world of liquid crystals within microfluidic confinements, typically channels with
dimensions of tens of micrometers. The present work is based on experiments with a roomtemperature
nematic liquid crystal, 5CB, and its colloidal dispersions within microfluidic devices
of rectangular cross-section, fabricated using standard techniques of soft lithography. To
begin with, a combination of physical and chemical methods was employed to create well defined
boundary conditions for investigating the flow experiments. The walls of the microchannels
were functionalized to induce dierent kinds of surface anchoring of the 5CB molecules:
degenerate planar, uniform planar, and homeotropic surface anchoring. Channels possessing
composite anchoring conditions (hybrid) were additionally fabricated, e. g. homeotropic and
uniform planar anchoring within the same channel. On filling the microchannels with 5CB
in the isotropic phase, dierent equilibrium configurations of the nematic director resulted,
as the sample cooled down to nematic phase. For a given surface anchoring, the equilibrium
director configuration varied also with the channel aspect ratio. The static director field
within the channel registered the initial conditions for the flow experiments. The static and
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dynamic experiments have been analyzed using a combination of polarization, and confocal
fluorescence microscopy techniques, along with particle tracking method for measuring the
flow speeds. Additionally, dual-focus fluorescence correlation spectroscopy is introduced as a
generic velocimetry tool for liquid crystal flows.
