Author
Shun Okudaira
Bio: Shun Okudaira is an academic researcher from Tokai University. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 2, co-authored 3 publications receiving 23 citations.
Papers
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TL;DR: For the first time, the molecular mechanism and structure of liquid crystalline materials as a function of concentration, temperature, and frequency is explained.
Abstract: Broadband dielectric spectroscopy has been used to analyze the temperature, frequency, and concentration dependences of the molecular dynamics of a nematic liquid crystal (5CB) mixed with the nonpolar solvent benzene. Differential scanning calorimetry measurement has been also performed to confirm the phase transitions of 5CB/benzene mixtures. The phase transition temperatures (crystalline to isotropic phases) thus obtained have been described very accurately from the temperature-dependent relaxation strength, the relaxation time, and the symmetric shape parameter of the relaxation function obtained from the fitting procedure. Two relaxation processes reflecting overall rotations around the short and long molecular axes are observed in both the nematic and isotropic phases. In the crystalline phase, the former process with the longer relaxation time disappeared, and latter process with shorter relaxation time shows a discontinuity at the freezing temperature. The relaxation process with shorter relaxation time obtained in the crystalline phase is larger than that obtained in the nematic phase because of the large restrictions in the crystalline phase. For the first time, we have precisely explained the molecular mechanism and structure of liquid crystalline materials as a function of concentration, temperature, and frequency.
19 citations
TL;DR: Surprisingly, the abnormal behavior of the isotropic phase was observed in LC/benzene mixtures that suggested the presence of local structure in the mixture, which set off the dipole moments along the long axis.
Abstract: Differential scanning calorimetry and broadband dielectric spectroscopy measurements were performed to investigate the phase transitions in nematic liquid crystal (LC)/benzene mixtures. Noticeable changes of the crystal-isotropic phase transition and the phase transition enthalpy were observed. We also estimated the number of unfreezable benzene molecules from the LC/benzene mixtures. The crystal-isotropic phase transition temperature was described very accurately from the temperature-dependent relaxation strength, the relaxation time, and the symmetric shape parameter obtained from the fitting procedure. Surprisingly, the abnormal behavior of the isotropic phase was observed in LC/benzene mixtures that suggested the presence of local structure in the mixture, which set off the dipole moments along the long axis. The interaction between the LC molecules was also discussed from the tau-beta diagram.
7 citations
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TL;DR: It is proposed that the polarization conductivity results from the local re-orientation of the μ(2)-OH dipoles bonded to the metal atom from the hybrid solid, i.e. Fe or Cr, and that dc conductivity, which can be ascribed to a proton propagation via a Grotthus mechanism, is favoured when the solvent molecules form strong hydrogen bonds between each other.
Abstract: The breathing behaviour of MIL-53(Cr) and MIL-53(Fe) upon water and ethanol desorption has been investigated by combining complementary experimental techniques including ThermoGravimetry Analysis (TGA), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS). It was shown that two stages of solvent departure are involved in the desorption process, as revealed by (i) a change of the weight loss gradient in the TGA curve, (ii) the existence of a second endothermic peak in the DSC signal and (iii) a sudden drop and/or profile change of the ac conductivity in CIS. All these features are observed around a typical temperature Tc, for which the framework contractions, caused by the solvent desorption, occur. Moreover, it is shown that these modifications are more pronounced when the magnitude of the breathing is higher, as illustrated by the comparison of the water/MIL-53(Cr), ethanol/MIL-53(Cr) and water/MIL-53(Fe) systems. CIS data were further analyzed in the light of DFT calculations which provided the preferential arrangements of the molecules within the pores and the resulting host/guest interactions. It could then be proposed that (i) the polarization conductivity results from the local re-orientation of the μ2-OH dipoles bonded to the metal atom from the hybrid solid, i.e. Fe or Cr, and (ii) that dc conductivity, which can be ascribed to a proton propagation via a Grotthus mechanism, is favoured when the solvent molecules form strong hydrogen bonds between each other.
40 citations
TL;DR: This review article is an effort to describe the advancements in LC and nanotechnology-assisted LC systems for developing an efficient biosensor of tunable performance and will serve as a guideline to researchers who aim to fabricate a nanotechnology -assisted LC materials-based biosensor for rapid, cost-effective, selective diagnostics of a targeted disease for health care management.
39 citations
TL;DR: It is suggested that for each nCB a unique, characteristic minimal value of ΔT, associated with the I-N-SmA triple point, exists and can be hidden in the negative pressures domain for 'shorter' nCBs, and the possibility of the extension of the 'melting curve' into thenegative pressures region as well as the appearance of the'melting inversion' at high enough pressures is indicated.
Abstract: Results of the extended Landau?de Gennes model analysis and experimental studies of the isotropic?nematic (I?N) and isotropic?smectic-A (I?SmA) phase transitions in rod-like liquid crystalline n-alkylcyanobiphenyls are presented. Experiments were carried out as a function of temperature and pressure using the static dielectric permittivity and its ?nonlinear? (strong electric field related) counterpart?the low-frequency nonlinear dielectric effect. Precise estimations of the values of the discontinuity of the isotropic?mesophase transitions (?T) for nCB from n?=?3?14 have been obtained. It is suggested that for each nCB a unique, characteristic minimal value of ?T, associated with the I?N?SmA triple point, exists. For ?shorter? nCBs it can be hidden in the negative pressures domain. The possibility of the extension of the ?melting curve? into the negative pressures region as well as the appearance of the ?melting inversion? at high enough pressures is indicated.
19 citations
TL;DR: In this article, the authors performed dielectric measurements on thermally aged carbon-black-filled chloroprene rubber (CR) and observed the primary and secondary processes were observed in unaged and thermally-aged CR.
16 citations
TL;DR: In this paper, the authors conducted dielectric and viscoelastic relaxation measurements for polystyrene (PS)/4-pentyl-4′-cyanobiphenyl (5CB) and PS/4- pentyl- 4′-cyclanoterphenyl(5CT) mixtures in the miscible state with the weight fractions of 5CB or 5CT from 0.04 to 0.27.
Abstract: We conducted dielectric and viscoelastic relaxation measurements for polystyrene (PS)/4-pentyl-4′-cyanobiphenyl (5CB) and PS/4-pentyl-4′′-cyanoterphenyl (5CT) mixtures in the miscible state with the weight fractions of 5CB or 5CT from 0.04 to 0.27 to examine the relationship between two-component dynamics in the mixture. Dielectric relaxation measurements mainly probed the dynamics of low-mass molecule (LM), 5CB or 5CT, because of the much larger dipole moment of LMs compared to that of PS. PS/5CB mixtures exhibited bimodal dielectric relaxation, while PS/5CT showed unimodal relaxation. The observed two relaxation modes (slow and fast modes) in PS/5CB were attributed to the full rotational motion and partial rotational motion of 5CB, respectively. The latter motion is allowed in the restricted space surrounded by less mobile PS matrix. In the case of 5CT, the fast mode was suppressed due to the larger size of 5CT molecule, and only the slow mode (rotational mode) appeared. The relaxation times of slow mod...
16 citations