Discotic Liquid Crystals in Nanoporous Solids: From the Structure and Dynamics to Local Charge Transport

Discotic liquid crystals embedded in nanoporous solids are very interesting hybrid materials with respect to fundamental questions in the physics and chemistry of confined molecular condensed matter. These systems find also increasing interest in organic electronics. Based on the results and expertise gained in our previous studies of these hybrid materials, the main objectives of this project are the exploration to what extent the competition between axial and radial order as well as the phase transitions in general can be influenced by varying the anchoring conditions for the molecules at the pore walls (surface grafting), the size of the discotic cores and/or by employing external magnetic fields. Moreover, we intend to explore how the structure, thermodynamics and molecular dynamics are affected by the resulting changed textures in the nanochannels, by the changed molecule/pore wall interaction and by a gradual filling of the nanochannels from the film-condensed state via the formation of capillary bridges to a complete filling of the channels. The latter will allow for a quantification of the thickness of the boundary layer, that is the layer in the pore wall proximity which is strongly affected by the interaction with the pore walls. To optimize the hybrid systems for real applications the considered pure discotic liquid crystals will be doped to obtain charge-transfer complexes by co-self-assembly. For the bulk systems this strategy has proven as very successful in order to optimize the electric transport properties. Thus, we intend to explore this approach also for the confined liquid crystalline state. Our objectives will be reached by a combination of structure sensitive methods (X-ray scattering, optical birefringence measurements, Differential Scanning Calorimetry etc.) with experiments which are related to the molecular mobility (dielectric spectroscopy, specific heat spectroscopy, in- and quasielastic neutron scattering). To relate the basic research to applications it will be tried to measure the local conductivity of the discotic liquid crystals directly in (isolated) cannels by an AFM-based approach. The project will highly benefit by the orthogonal expertise of both proposers. The successful realization of the project requires an intense cooperation between the two research groups because structure determines the molecular dynamics and vice versa. To warrant this intense cooperation joint project meetings and the exchange of the PhD students for complementary measurements as well as complementary training are plant (additionally to sample exchange). Besides the expected synergistic benefit on the scientific results both PhD students will significantly profit in their scientific education from the cooperative spirit of this research project.

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