Lyotropic liquid crystals are extensively studied as drug delivery systems for dermal and
parental applications and for applications in oral cavity. They are formed spontaneously, by
addition of the solvent (water/oil) to amphiphilic molecules. Various mesophases formed
can be divided by their arrangement in the solvents to hexagonal, cubic and lamellar phases.
Each phase has its unique physio-chemical features. Various analytical methods are used for
their investigation, however in many cases a combination of techniques is used in order to
obtain complementary and more reliable data.
In the thesis, the supramolecular structure of liquid crystals based on lecithin and Tween 80®
as surfactant mixture, oil phase isopropyl myristate and water was evaluated using electron
paramagnetic resonance. Different spin probes, which report about actions in a specific local
environment of supramolecular structures in which they are located, were built into the
systems. Samples spectra were recorded at temperatures between 22 °C and 62 °C. Regions
near water-lipid layer have a high order parameter, are very viscous and give anisotropic
spectra, while the areas in the inner part of the membrane are highly fluid; mobility of the
molecules is high. Order of phases was lowered by enlargement of water content as well as
with higher temperatures. On the other hand, minimal differences between samples were
observed with increasing temperature. Based on the water component content, the system
with the lowest water content had hexagonal structure, the system with the highest water
content was identified as phase transition system between lamellar and micellar phase, while
the systems in between had lamellar structure with the possibility of presence of rod-like
micelles. Similar conclusions have been made for these systems based on other analytical
techniques as well. Composition of each spectrum from three different components,
representing a defined type of domain with its distinguished physio-chemical properties, was
shown with EPR spectra simulations. Association of domains was observed at higher
temperatures. We were keen to investigate the potential of phase transition between different
phases as well. This phenomenon was evaluated by slowly heating the samples and was not
observed for liquid crystals systems tested. The phase transition is not a desired property of
liquid crystals, which are used as carriers for various routs of applications.
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