Photosensitive materials are important objects for basic research and have numerous applications
such as holographic recording, photomechanical devices etc. One class of photosensitive materials are anisotropic soft matters,
namely liquid crystals (LCs). The academic LC research has been shifted from the display industry towards the search for novel
functional LC materials applicable in diverse fields such as micro-, nano, biotechnology, medicine, polymer and colloid science.
Study of these, for LCs novel fields, besides the new LC compounds of desired properties also require well-determined
and well-controlled boundary conditions. Microfluidics is an emerging multidisciplinary research field that has grown enormously
in the last two decades. Moreover, the expansion of this scientific field is immediately followed by technological advance
in the area like medical diagnostics, pharmaceuticals, chemical and food industry, agriculture, etc.
The proposed work will explore novel ways of flow control by light in microfluidic environment that the photosensitive LCs offer.
To date, all three main components of the microfluidic systems (the micro-channel architecture, the fluidic transport medium and the units
for control and manipulation of the fluid flow) typically use isotropic materials.
Our aim is to show that the use of anisotropic, photosensitive LCs as a carrier fluid provides the possibility of
routing, mixing and sorting of flow channels that are not possible with ordinary (isotropic) materials.
The work relies on the possibility to induce significant changes in physical properties
of LCs, or even phase transitions by illumination. The research on these, photochromic
LCs will focus on novel azo- and stilbene-based LC dimers that consist of two promesogenic
photoactive units linked by a flexible spacer. The azo-compounds exhibits a 4-donor-4-acceptor substitution,
i.e., bearing a push-pull configuration for which both the photoinduced trans-to-cis (E/Z) isomerization and the
thermal cis-to-trans back-reaction are fast enough for microfluidic application.
The key questions regarding the novel photochromic dimeric or bent core LCs are:
(i) how fast are the photoinduced phase transitions?
(ii) what light intensities are required?
(iii) how the visco/elastic properties of the compounds change upon the illumination with different intensities?
The tasks will include: (1) Characterization of the novel photochromic dimeric and bent-core LCs and testing their photosensitivity for microfluidic applications.
(2) The construction of the phase diagrams for the compounds including “illumination-temperature’ phase diagram.
(3) Photo-rhelogical measurements for the novel photochromic dimeric and bent-core LCs to
determine the viscoelastic properties and the influence of the illumination on them.
(4) In situ microfluidic tests.
MSc degree in physics, or related fields, general interests in soft matter physics and/or optics,
good communication skills in English, affinity for experimental work.