Magnetically active anisotropic composite systems - MACOSYS

Project summary

The widespread acquaintenance of liquid crystals is based on today’s liquid crystal display technology (LCD). There are also other important devices (less well known to the public) relying on liquid crystals like optical switches, photo-elastic-modulators, tunable lasers, tunable filters, etc. These devices for functioning take the use of the anisotropy (orientational dependence) in the optical and electric properties of liquid crystals. Liquid crystals are magnetically anisotropic too, however, in general, the magnetic anisotropy is much smaller than the anisotropy of the electric properties. It has been predicted theoretically in early 70’s that the magnetic sensitivity of liquid crystals can be greatly increased by doping them with magnetic particles. This assumption has been confirmed experimentally in the 80’s. Moreover, very recently (after 2010), new discoveries have been made regarding the optical response of such liquid crystals doped with nanoparticles to very low magnetic fields . Our project proposal targets these novel findings at very low magnetic fields (especially regarding the relevant experimental conditions), and the major problem that prevents the real application of these liquid crystals (e.g., as magneto-optical devices), namely, the aggregation of the nanoparticles. In our project we also propose a novel class of materials – self-standing films of cross-linked liquid crystalline elastomers doped with magnetic nanoparticles potentially having unique magneto-optical and magneto- mechanical properties. The key questions targeted by the project proposal (and the hypothesis how the experiments may answer the question) are: - under which conditions is the application of the small bias magnetic field crucial for the optical response of ferronematics at low magnetic fields? (a possible answer expected from the experiments with and without the bias magnetic field); - how the initial pretilt angle relates to the bias magnetic field and to the response (both optical and dielectric) to low magnetic fields? (a possible answer expected from the experiments by changing the direction of the bias magnetic field and that of the pretilt angle); - besides the restoring elastic interactions, which other factors/interactions give contribution to the aggregation of nanoparticles in ferronematics? (studies of the aggregation process for different type of nanoparticles, for homogeneously as well as for periodically distorted initial state of the nematic liquid crystal host material); - can the magnetic field induced shift of the phase transition temperature be considerably enhanced? (to our expectations in ferronematics based on bent-core nematics); - can one produce a magnetically sensitive, optically anisotropic self standing film? (by doping liquid crystalline polymers with magnetic nanoparticles prior the aligning and cross-linking process). On the one hand, the increased sensitivity of ferronematics to magnetic fields regarding their optical and dielectric responses, as well as the enhancement of the magnetically induced shift in the phase transition temperature – which are the main objectives of the project proposal – could certainly trigger further experimental and theoretical research in the expanding field of magnetoactive composite materials. On the other hand, but not less importantly, these objectives of the project, together with a better understanding of the aggregation process of nanoparticles (another key objective of the proposal) are directly related to the questions/problems that have prevented ferronematics from the realization of practical applications in various magneto-optical or magneto-mechanical devices. Therefore, the present project proposal has a considerable importance from the viewpoint of potential technological applications too.