TY - CONF A1 - Krause, Christina A1 - Yin, Huajie A1 - Schönhals, Andreas T1 - Molecular dynamics of a discotic liquid chrystal T2 - 76th Annual Meeting of the DPG and DPG Spring Meeting CY - Berlin, Germany DA - 2012-03-25 PY - 2012 AN - OPUS4-25637 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krause, Christina A1 - Frick, B. A1 - Zorn, R. A1 - Schönhals, Andreas T1 - Vibrational Density of States and Molecular Dynamics of Discotic Liquid Crystals in the Bulk and in the Nanoconfined State Investigated by Neutron Scattering T2 - DPG Spring Meeting CY - Regensburg, Germany DA - 2013-03-10 PY - 2013 AN - OPUS4-28759 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krause, Christina A1 - Yin, Huajie A1 - Wurm, Andreas A1 - Schick, C. A1 - Schönhals, Andreas T1 - Molecular dynamics of a discotic liquid crystal studied by dielectric relaxation and specific heat spectroscopy T2 - DPG Spring Meeting CY - Regensburg, Germany DA - 2013-03-10 PY - 2013 AN - OPUS4-28760 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, Christina A1 - Schönhals, Andreas T1 - Phase transitions and molecular mobility of a discotic liquid crystal under nanoscale confinement N2 - The phase behavior and the molecular dynamics of a pyrene-based discotic liquid crystal when confined in nanoporous aluminum membranes with different pore sizes is studied by broadband dielectric spectroscopy and differential scanning calorimetry. In confinement the two phase transitions between plastic crystalline and hexagonal ordered phase at lower and from the latter to an isotropic state at higher temperatures are also observed, but two different phase structures close to the wall and in the pore center are evidenced by two peaks in the heat flow for the first time. While the former peak is independent of the pore size, the depression of the phase transition temperatures of the latter ones can be described by the Gibbs–Thomson equation. With decreasing pore size for both phase transitions the transition enthalpies decrease. A critical pore size for phase transformation of about 20 nm is estimated from the pore size dependence of the transition enthalpies. Like for the bulk, an a-relaxation is also observed in confinement. At the phase transition its relaxation rates show a discontinuity from which a dielectric phase transition temperature can be extracted. For temperatures above and below the phase transition the temperature of the relaxation rate can be approximated by an Arrhenius equation. The pore size dependence of the estimated apparent activation energies is ascribed to the interplay between pore size and interaction effects. The cooperative nature of the underlying molecular dynamics is indicated by the occurrence of the well-known compensation law. PY - 2013 DO - https://doi.org/10.1021/jp406010d SN - 1932-7447 SN - 1089-5639 VL - 117 IS - 38 SP - 19712 EP - 19720 PB - Soc. CY - Washington, DC AN - OPUS4-29336 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krause, Christina A1 - Emmerling, Franziska A1 - Schönhals, Andreas T1 - Triphenylene-based discotic liquid crystals T2 - 7th Conference of the International Dielectric Society CY - Leipzig, Germany DA - 2012-09-03 PY - 2012 AN - OPUS4-26504 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, Christina A1 - Yin, Huajie A1 - Cerclier, C. A1 - Morineau, D. A1 - Wurm, Andreas A1 - Schick, C. A1 - Emmerling, Franziska A1 - Schönhals, Andreas T1 - Molecular dynamics of a discotic liquid crystal investigated by a combination of dielectric relaxation and specific heat spectroscopy N2 - The molecular dynamics of the discotic liquid crystal pyrene-1,3,6,8-tetracarboxylic tetra(2-ethylhexyl)ester is studied by dielectric relaxation and specific heat spectroscopy. Dielectric spectroscopy shows 3 processes: a β-relaxation at low temperatures and an α-relaxation in the temperature range of the mesophases followed by conductivity. The dielectric α-relaxation is assigned to a restricted glassy dynamics in the plastic crystal as well as in the liquid crystalline phase. The obtained different Vogel–Fulcher–Tammann laws (different Vogel temperatures and fragility) are related to the different restrictions of the dipolar fluctuations in the corresponding phases. By means of specific heat spectroscopy glassy dynamics is also detected in the plastic crystalline phase but with quite a different temperature dependence of the relaxation times. This is discussed considering the different probes involved and how they are influenced by the structure. In the frame of the fluctuation approach a correlation length of glassy dynamics is calculated to 0.78 nm which corresponds to the core–core distance estimated by X-ray scattering. PY - 2012 DO - https://doi.org/10.1039/c2sm25610j SN - 1744-683X VL - 8 IS - 43 SP - 11115 EP - 11122 PB - RSC Publ. CY - Cambridge AN - OPUS4-26826 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krause, Christina A1 - Yin, Huajie A1 - Schönhals, Andreas A1 - Wurm, Andreas A1 - Schick, Ch. T1 - Molecular dynamics of a discotic liquid crystal T2 - 7th Conference of the International Dielectric Society CY - Leipzig, Germany DA - 2012-09-03 PY - 2012 AN - OPUS4-26487 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krause, Christina A1 - Yin, Huajie A1 - Wurm, Andreas A1 - Schick, C. A1 - Schönhals, Andreas T1 - Glassy-like dynamics in a discotic liquid crystal revealed by broadband dielectric and specific heat spectroscopy T2 - 7th International Discussion Meeting on Relaxations in Complex Systems CY - Barcelona, Spain DA - 2013-07-21 PY - 2013 AN - OPUS4-28882 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yildirim, Arda A1 - Krause, Christina A1 - Huber, P. A1 - Schönhals, Andreas T1 - Multiple glassy dynamics of a homologous series of triphenylene-based columnar liquid crystals – A study by broadband dielectric spectroscopy and advanced calorimetry N2 - Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n = 5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations probing the molecular mobility, a c-relaxation due to localized fluctuations as well as two glassy dynamics, the acore- and aalkyl-relaxation, were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n = 8 from a rigid constrained (n = 5,6) to a softer system (n = 10,12) was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene-like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition. KW - Discotic liquid crystals KW - Broadband dielectric spectroscopy KW - Advanced calorimetry PY - 2022 DO - https://doi.org/10.1016/j.molliq.2022.119212 VL - 358 SP - 1 EP - 10 PB - Elsevier B.V. AN - OPUS4-54721 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Yildirim, Arda A1 - Krause, Christina A1 - Zorn, R. A1 - Schönhals, Andreas T1 - Multiple glassy dynamics of a homologous series of triphenylene-based columnar liquid crystals – A study by broadband dielectric spectroscopy, advanced calorimetry and Neutron Scattering N2 - Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n=5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations a γ-relaxation due to localized fluctuations as well as two glassy dynamics the αcore and αalkyl relaxation were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n=8 from a rigid constrained (n=5,6) to a softer system (n=10,12) on a molecular lenght scale was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition. The results were confirmed by in- and quasielastic neutron scattering T2 - Confit 2022 CY - Grenoble, France DA - 10.10.2022 KW - Glassy Dynamics KW - Discotic Liquid Crystals PY - 2022 AN - OPUS4-56661 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -