Structure, Dynamics and Phase Behavior of a Discotic Liquid Crystal Confined in Nanoporous Anodic Aluminum Oxide Membranes

  • Discotic liquid crystals (DLCs) are a promising class of soft matter for electronic applications. This is due to their ability to organize and stack themselves into columns in a hexagonal columnar mesophase, a mesophase in between the plastic crystalline and isotropic phase, driven by the overlap of the π orbitals of their aromatic core. This leads to a high charge-carrier mobility along the column axis. Further, these columns could then be considered as “molecular nanowires”. Spatial confinement of soft matter in nanoporous media influences its structure, thermodynamic properties, and mobility. Embedding liquid crystals and polymers into nanopores of anodic aluminum oxide (AAO) results in a 2D nanoconfinement of these materials. This confinement affects their properties, compared to the bulk, such as phase transition temperatures and enthalpies, molecular mobility, and architecture of the crystallization. In this study, 2,3,6,7,10,11 hexakis[hexyloxy] triphenylene (HAT6), aDiscotic liquid crystals (DLCs) are a promising class of soft matter for electronic applications. This is due to their ability to organize and stack themselves into columns in a hexagonal columnar mesophase, a mesophase in between the plastic crystalline and isotropic phase, driven by the overlap of the π orbitals of their aromatic core. This leads to a high charge-carrier mobility along the column axis. Further, these columns could then be considered as “molecular nanowires”. Spatial confinement of soft matter in nanoporous media influences its structure, thermodynamic properties, and mobility. Embedding liquid crystals and polymers into nanopores of anodic aluminum oxide (AAO) results in a 2D nanoconfinement of these materials. This confinement affects their properties, compared to the bulk, such as phase transition temperatures and enthalpies, molecular mobility, and architecture of the crystallization. In this study, 2,3,6,7,10,11 hexakis[hexyloxy] triphenylene (HAT6), a triphenylene-based DLC, was confined into nanoporous AAO membranes. The structure, dynamics and the phase behavior of the confined HAT6 were investigated by broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). HAT6 was embedded into nanoporous AAO membranes by melt infiltration in the isotropic phase under argon atmosphere. The membranes have parallel aligned cylindrical nanopores, with different pore diameters in the range of 10-180 nm. Bulk HAT6 forms a hexagonal columnar phase; in between the isotropic phase above 371 K and the plastic crystalline phase below 340 K. Unlike the bulk, the confined HAT6 split the phase transitions in two or more, which might be interpret as different phase structures; close to the wall and at the pore center. Moreover, the phase transitions of the confined HAT6 shifted, with decreasing pore diameter, to lower temperatures. The dependencies of the phase transition temperatures on the pore size was well-described by the Landau-de Gennes model. Furthermore, pore surfaces of a series of membranes were chemically modified, resulting in a more hydrophobic pore surface than the unmodified ones. HAT6 was embedded into the modified membranes by the same aforementioned preparation. The influence of the changed host-guest-interaction, on the structure, dynamics, and the phase behavior of HAT6 confined in the modified membranes, was also investigated by BDS and DSC.zeige mehrzeige weniger

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Metadaten
Autor*innen:Arda Yildirim
Koautor*innen:K. Sentker, P. Huber, Andreas Schönhals
Dokumenttyp:Vortrag
Veröffentlichungsform:Präsentation
Sprache:Englisch
Jahr der Erstveröffentlichung:2017
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Freie Schlagwörter:Discotic Liquid Crystals; Nanoconfinement
Veranstaltung:Liquids 2017 – 10. Liquid Matter Conference
Veranstaltungsort:Ljubljana, Slovenia
Beginndatum der Veranstaltung:17.07.2017
Enddatum der Veranstaltung:21.07.2017
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:01.08.2017
Referierte Publikation:Nein
Eingeladener Vortrag:Nein
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