Publications (12)66.68 Total impact

  • I. TEUCHER · H. Baessler · M. M. Labes
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    ABSTRACT: THE significance of liquid crystalline phases in biological systems1 has been the subject of much discussion. The occurrence of mesoforms in membrane structures1 and the known response of lyotropic2, nematic3, and Cholesterin 4-6 meso-phases to magnetic fields have led to the speculation that a possible mechanism for the interaction of a weak magnetic field (~ 1,000 Oe) with a biological system is through influence on the rates of mass or charge transport through a membrane7. We have undertaken measurements of the diffusion of small molecules and ions through liquid crystal films to investigate this possibility, and report here preliminary values for the diffusion constant of tritium through two nematic liquid crystals, and evidence for a magnetic field effect on this constant.
    No preview · Article · Jan 1971 · Nature
  • H. Baessler · M. M. Labes · T. M. Laronge
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    ABSTRACT: By measuring changes in the dielectric constant of a 1.75:1 cholesteryl chloride-cholesteryl myristate (CM) mixture in the presence of magnetic fields H up to 10 kG, the orientation of the molecular and helical axes with respect to the field direction can be deduced, and the possibility of a dependence of the alignment process on the pitch Z of the helix is explored. When the sample thickness is much greater than Z, there is no preferred direction for the helix axis in the bulk, and applying H either ⊥. or || to the sample causes the helix axis to align || H. This effect only occurs at Z>10 μ, and only partial ordering occurs even at Tnematio. The angle δ between the long molecular axis of cholesteryl chloride and a plane ⊥ to the helix axis is reduced by application of H. Since δ is determined by the internal mechanical energy of the cholesteric structure, the decrease in δ becomes more pronounced as Z approaches infinity. A comparison is also made of the effects of electric and magnetic fields on CM; an electric field of 500 V/cm counteracts a magnetic field of the order of 10 kG. The anisotropy of the diamagnetic susceptibility is deduced to be ∼10-9.
    No preview · Article · Oct 1970 · The Journal of Chemical Physics
  • H. Baessler · M. M. Labes
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    ABSTRACT: Electric field strength and helix pitch relationship in induced cholesteric-nematic phase transitions
    No preview · Article · Oct 1970 · Physical Review Letters
  • H. Baessler · M. M. Labes
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    ABSTRACT: Measurements of dielectric constants of a cholesteryl chloride-cholesteryl myristate mixture having a strongly temperature-dependent helical pitch have been performed in the presence and absence of an applied dc electric field. An analysis of the molecular arrangement in samples oriented by wall effects is presented, as well as the perturbations in this arrangement which occur both thermally and by the application of an electric field. Elastic moduli of bending and torsional strain are estimated from the threshold electric fields observed to (a) induce helical perturbation and (b) destroy the helical structure in the transition to a nematic phase.
    No preview · Article · Oct 1970 · The Journal of Chemical Physics
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    H. Baessler · M. M. Labes · T. M. Laronge
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    ABSTRACT: By studying the optical rotatory power (OR) of a compensated cholesteric helical structure, it is possible to observe both thermally induced helical inversion and electric field perturbations of the helix. For a cholesteryl chloride-cholesteryl myristate 1.75:1 mixture, the OR changes sign at T= r(nematic) =42° increasing to infinity prior to the inversion. Upon application of a dc electric field parallel to the helix axis, the OR decreases continuously and reversibly by a factor of 4 in the field range 0.25F u<F<F0, where Fu denotes the critical field required to induce a nematic transition. This effect cannot be explained as a macroscopic reordering of the material, but is rather due to a decrease in pitch accompanying a conical helical perturbation. This perturbation arises from bending forces tending to align the dipole moments of cholesteryl chloride in the field direction. When a dc field is applied perpendicular to the helix axis, the pitch diverges logarithmically to infinity as F approaches the critical value for inducing a transition.
    Preview · Article · Oct 1970 · The Journal of Chemical Physics
  • H. Baessler · R. R. Beard · M. M. Labes
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    ABSTRACT: Dipole relaxation and molecular arrangements in liquid crystals
    No preview · Article · Oct 1970
  • H. Baessler · R. B. Beard · M. M. Labes
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    ABSTRACT: The real and imaginary parts of the dielectric constant of a 1.75:1.00 mixture of cholesteryl chloride and cholesteryl myristate have been measured in the frequency range 1 kHz–10MHz. Two modes of molecular rotation are found to contribute to dipole relaxation: rotation of cholesteryl chloride around a short molecular axis (process R 1 ) and rotation of cholesteryl myristate around a long molecular axis (R 2 ) . The relaxation frequency associated with R 1 changes by not more than a factor of 2 when going from the cholesteric phase to the isotropic melt or to a field‐induced aligned nematic phase. This indicates that the potential barrier hindering molecular rotation is determined by short‐range order rather than long‐range order. From the magnitude of the dielectric increment, conclusions are drawn regarding the molecular arrangement in the various phases. The temperature dependence of the relaxation frequency is analyzed in terms of absolute rate theory.
    No preview · Article · Apr 1970 · The Journal of Chemical Physics
  • H. Baessler · M. M. Labes
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    ABSTRACT: Cholesteric liquid crystal pitch from IR transmission measurements
    No preview · Article · Feb 1970
  • H Baessler · M M Labes
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    ABSTRACT: Shifts in the nematic temperature of a compensated cholesteric liquid‐crystal solvent, consisting of cholesteryl chloride and cholesteryl myristate, are caused by adding steroidal solutes. A helical twisting power P can be defined which is a molecular property; there is a linear dependence of the inverse of the solute concentration on the helical pitch. The method has the advantages of (1) allowing study of compounds which do not form mesophases themselves and (2) eliminating temperature effects. For a series of fatty acid esters of cholesterol, P decreases with decreasing number of carbon atoms in the ester chain, and shows a zigzag fine structure with P having higher values for odd‐numbered carbon‐atom chains. P, and therefore the helix, changes rotational senses if the ester chain is replaced by Cl, Br, or OH. Changes are also discussed associated with modification of the 17 side chain or the steroid ring system itself. A model is proposed attributing P to the molecular asymmetry at the 3β position of the steroid ring, which can cause macroscopic twist if two lever arms are present, one of which lacks rotational symmetry.
    No preview · Article · Feb 1970 · The Journal of Chemical Physics
  • H. Baessler · M. M. Labes · P. A. G. Malya · W. R. Nes
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    ABSTRACT: Thermally induced helical inversion absence in single component cholesteric liquid crystals indicating impurity compensation
    No preview · Article · Feb 1970
  • H. Baessler · M. M. Labes · T. M. Laronge · I. Teucher
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    ABSTRACT: Electric and magnetic field effects on structure and properties of cholesteric liquid crystals
    No preview · Article · Jan 1970
  • H. Baessler · M. M. Labes
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    ABSTRACT: In order to determine whether interaction between the permanent or the induced molecular dipole moments of a cholesteric liquid crystal and an applied electric field is responsible for inducing a transition to a nematic phase, ac‐field measurements were performed. In a mixture of cholesteryl chloride and cholesteryl myristate, phase transitions can be induced by an ac field of a frequency up to a threshold value fpt;fpt is approximately equal to the relaxation frequency for rotation of cholesteryl chloride molecules around a short molecular axis which has recently been determined by dielectric measurements. A relation between the rms field and fpt is derived and experimentally verified. The absence of ferroelectric ordering in the induced and aligned nematic phase is demonstrated.
    No preview · Article · Dec 1969 · The Journal of Chemical Physics