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Item type:Publication, Access status: without files , Confinement-suppressed phase transition and dynamic self-assembly of ionic superdiscs in ordered nanochannels: Implications for nanoscale applications(American Chemical Society (ACS), 2023-09-08); ; ; ; Ionic liquid crystals are ionic liquids that exhibit liquid crystalline mesomorphism together with ionic conductivity. As is known, confined liquid crystal mesophases can show anomalous dynamics and phase behavior. Investigations considering the factors controlling the macroscopic properties of ILCs in confinement are rare in the literature. This study reports the molecular mobility and the phase transition behavior of a guanidinium-based columnar ILC confined in the nanopores of self-ordered anodic aluminum oxide membranes of various pore diameters (25-180 nm) using broadband dielectric spectroscopy (BDS), calorimetry, and X-ray scattering. It is aimed at revealing in which way the pore size as well as the pore surface wettability (hydrophobic or hydrophilic) alter the molecular dynamics and phase transition behavior of this system. These properties are crucial for applications. The DSC investigations reveal the following: (i) the phase transition temperature for the transition from the plastic crystalline to the crystalline-liquid state has nonmonotonic dependence versus the inverse pore diameter; and (ii) the transition from the liquid crystalline to the isotropic phase is suppressed for all nanoconfined samples. This transition suppressed in the thermal signal was made evident by BDS and X-ray scattering. It is discussed as a continuous phase transition taking place in the pores instead of a discontinuous first-order transition, as observed for the bulk. BDS investigations show different relaxation processes for bulk and nanoconfined ILC. The molecular origins of various relaxation processes are discussed and suggested. It is further shown that the self-assembly of this ILC is dynamic in nature, which might apply for other ILCs too. The obtained results will have implications for nanoscale applications of ionic liquid crystals.Publicationtype: Journal Article11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Side chain length-dependent dynamics and conductivity in self-assembled ion channels(Soc., 2022-06-30); ; ; ; We study the molecular mobility and electrical conductivity of a homologous series of linear shaped columnar ionic liquid crystals ILCn, (n = 8, 10, 12, 14, 16) using broadband dielectric spectroscopy (BDS), specific heat spectroscopy (SHS), and X-ray scattering. We aim to understand how the alkyl chain length influences the dynamics and electric conductivity in this system. Two dielectrically active relaxation modes are observed, the γand the αcore process, that correspond to the localized fluctuations of the alkyl chains and cooperative motions of the aromatic core in the columns, respectively. Both the γrelaxation and the αcore process slow down with increasing alkyl chain length. SHS reveals one relaxation process, the αalkyl process that has a similar temperature dependence as that of the αcore process for ILC12, 14, and 16 but shifts to higher temperature for ILC8 and 10. For ILC12, 14, and 16, the absolute values of DC conductivity increase by 4 orders of magnitude at the transition from the plastic crystalline to hexagonal columnar phase. For ILC8 and 10, the DC conductivity behavior is similar to ionic liquids, where the conductivity is coupled with structural relaxation. Small-angle X-ray investigations reveal that both the intercolumnar distance and the disorder coherence length increase with alkyl chain length; conversely, the DC conductivity decreases monotonically.Publicationtype: Journal Article29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Collective orientational order and phase behavior of a discotic liquid crystal under nanoscale confinement(Royal Society of Chemistry (RSC), 2019); ; ; ; The phase behavior and molecular ordering of hexakishexyloxy triphenylene (HAT6) DLCs under cylindrical nanoconfinement are studied utilizing differential scanning calorimetry (DSC) and dielectric spectroscopy (DS), where cylindrical nanoconfinement is established through embedding HAT6 into the nanopores of anodic aluminum oxide (AAO) membranes, and a silica membrane with pore diameters ranging from 161 nm down to 12 nm. Both unmodified and modified pore walls were considered. In the latter case the pore walls of AAO membranes were chemically treated with n-octadecylphosphonic acid (ODPA) resulting in the formation of a 2.2 nm thick layer of grafted alkyl chains. Phase transition enthalpies decrease with decreasing pore size, indicating that a large proportion of the HAT6 molecules within the pores has a disordered structure, which increases with decreasing pore size for both pore walls. In the case of the ODPA-modification, the amount of ordered HAT6 is increased compared to the unmodified case. The pore size dependencies of the phase transition temperatures were approximated using the Gibbs-Thomson equation, where the estimated surface tension is dependent on the molecular ordering of HAT6 molecules within the pores and upon their surface. DS was employed to investigate the molecular ordering of HAT6 within the nanopores. These investigations revealed that with a pore size of around 38 nm, for the samples with the unmodified pore walls, the molecular ordering changes from planar axial to homeotropic radial. However, the planar axial configuration, which is suitable for electronic applications, can be successfully preserved through ODPA-modification for most of the pore sizes.Publicationtype: Journal ArticleScopus© Citations 23 114 124