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Show more[No abstract available] Appropriate credit for the requested material should be given as follows: "Reprinted (adapted) with permission from Langmuir 7:9, 1988-1990. Copyright 1991 American Chemical Society."
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Show moreThe electroclinic effect and dielectric response have been investigated in the British Drug House material SCE12 over its entire 15-K smectic-A range. Near the smectic-Asmectic-C*-phase transition both the electroclinic coefficient and dynamic response behave normally, the former diverging and the latter exhibiting a critical slowing down on approaching TA-C* from above. Similar behavior is seen in the dielectric response. Approximately 10 to 12 K above TA-C*, however, it was found that the electroclinic relaxation time levels off and even begins to increase again on approaching the nematicsmectic-A transition from below. The magnitude of the electroclinic coefficient, however, decreases monotonically on approaching the nematicsmectic-A transition. © 1991 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Li Z., Akins R.B., Dilisi G.A., Rosenblatt C., Petschek R.G., Physical Review A 43:2, 852-857 (1991). Copyright 1991 by the American Physical Society".
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Show moreAn investigation on the cyclic liquid crystalline trimer TPB-(c)9(3) was performed. The optical retardation and Fréedericksz techniques within a few tens of millikelvins of the superheating limit of the nearly second-order nematic isotropic phase transition were used for the investigation purpose. It was found that both the Fréedericksz bend threshold voltage and optical retardation were in good agreement with tricritical behaviour for the transition. Appropriate bibliographic citation and notice of the APS copyright must be included- "Syed I.M., Percec V., Petschek R.G., Rosenblatt C., Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 67:1, 117041-117044 (2003). Copyright 2003 by the American Physical Society."
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Show moreFreedericksz measurements were performed on mixtures of a nematic mesogen and a V-shaped molecule. The bend elastic constant was found to decrease significantly with increasing concentration of the V-shaped molecule. The results are discussed theoretically, taking into account the detailed structure of the molecules. ©2000 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Dodge M.R., Rosenblatt C., Petschek R.G., Neubert M.E., Walsh M.E., Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 62:4 B, 5056-5063 (2000). Copyright 2000 by the American Physical Society."
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Show moreUsing an atomic force microscope to nanopattern a substrate for liquid crystal alignment, a bend distortion is imposed on a liquid crystal. In regions of large bend the smectic-A phase melts into the nematic phase, and the width of the melted region is measured as a function of temperature. The results are consistent with type-I superconducting (nematic-smectic-A) behavior, wherein a large magnetic field (bend or twist distortion) induces an order to disorder transition. A model that accounts for non-mean-field behavior is presented. © 2006 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Wang R., Syed I.M., Carbone G., Petschek R.G., Rosenblatt C., Physical Review Letters 97:16, 2006. Copyright 2006 by the American Physical Society."
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Show moreKerr measurements, ellipsometry, and quasielastic light scattering have been used to probe nematic fluctuations and nematic wetting at an isotropic liquid crystal-substrate interface in four generations of liquid crystalline monodendrons and dendrimers. We find that the pretransitional behavior is qualitatively similar to that of low molecular weight liquid crystals, exhibiting a Landau-like divergence of the relaxation time and a logarithmic divergence of the optical retardation on approaching the nematic-isotropic phase transition from above. Quantitatively, we find that the transition temperatures of the monodendrons are typically about 0.5 K above the supercooling limit of the isotropic phase and that the orientational viscosities may be fit to a power law in molecular weight Mn, where the exponent ≤ 1.0. Appropriate credit for the requested material should be given as follows: "Reprinted (adapted) with permission from Macromolecules 29:24, 7813-7819. Copyright 1996 American Chemical Society."
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Show moreThe spatial and temperature dependence of the surface-induced orientational order parameter S(z,T) was determined in the isotropic phase. An optical fiber was immersed in a thin liquid crystal layer and the retardation was measured as a function of the fiber's height above the surface, from which the model-independent S(z,T) was deduced with resolution 2nm. It was found that (i) S(z=0) 0.12 close to the nematic transition temperature, (ii) the susceptibility is mean-field-like, and (iii) S(z,T) deviates significantly from exponential spatial decay. The results are discussed in terms of a nonlocal potential. © 2009 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Lee J.-H., Atherton T.J., Barna V., De Luca A., Bruno E., Petschek R.G., Rosenblatt C., Physical Review Letters 102:16, 2009. Copyright 2009 by the American Physical Society."
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Show moreThe effective response time eff of the nematic-electroclinic effect was determined as a function of driving frequency and temperature. Near the nematicsmectic-A transition temperature TNSm-A, eff was found to be a function of driving frequency, indicating the existence of more than one physical process. Several degrees above TNSm-A, eff was found to be frequency independent up to 100 kHz. At these temperatures, moreover, the effective response times are quite small, of order 100 ns. © 1991 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Li Z., Ambigapathy R., Petschek R.G., Rosenblatt C., Physical Review A 43:12, 7109-7112 (1991). Copyright 1991 by the American Physical Society."
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Show moreSmall quantities of the floppy bimesogen di(4PPB5)3Si were dissolved in an anticlinic liquid crystal consisting of a mixture of left-handed and right-handed TFMHPOBC, with enantiomer excess X=0.2. The bimesogen dopant was found to promote anticlinic order with an anticlinic interaction coefficient per molecule udopant smaller than, but of the same order as, that of the rigid bent-core dopant P-7PIMB. For both dopants udopant was found to be much larger than that due to a pair of TFMHPOBC molecules in adjacent layers. The results are examined in terms of both the flexibility of the group linking the two legs of each dopant, as well as their chemical structure. © 2005 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Zhu M.H., Petschek R.G., Rosenblatt C., Komitov L., Olsson N., Helgee B., Kim J.M., Neubert M.E., Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 72:2, 1-5, 2005. Copyright 2005 by the American Physical Society."
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Show moreA dc electric field was applied perpendicular to the tilt plane of a pitch-compensated (unwound helix) anticlinic liquid crystal. By means of quasielastic light scattering, the field was found to couple the acoustic and optic Goldstone modes, resulting in an increase of the relaxation time τβ of the acoustic like eigenmode. Elastic constants were estimated from the relaxation time data. ©2000 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Zhang S., Keast S.S., Neubert M.E., Petschek R.G., Rosenblatt C., Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 62:5 B, R5911-R5914 (2000). Copyright 2000 by the American Physical Society."
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Show moreMeasurements of reflectivity versus ac electric field E were performed in the nematic phase of octylcyanobiphenyl homeotropically aligned between two indium tin oxide coated glass slides. The change in reflectivity R was found to be linear in E, with d(R)/dE increasing monotonically toward the nematic-isotropic transition temperature. In addition, the phase of R at the front and back surfaces differed by. Such an effect will arise from t/Iorder electricity, whereby a term proportional to the product of the electric field and the gradient of the nematic order parameter appears in the bulk free energy. This term integrates to yield a pair of surface terms such that there is a y/Ilinear change in the order parameter close to the interface. Similar terms will also arise from ferroelectric interactions at the surface. © 1992 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Tripathi S., Petschek R.G., Rosenblatt C., Physical Review A 45:6, R3387-R3390 (1992). Copyright 1992 by the American Physical Society."
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Show moreThe optical retardation of a liquid crystal above the nematic-isotropic phase transition temperature TNI and subjected to planar alignment conditions at the substrate was investigated in the presence of an electric field applied normal to the substrates. The response was found to exhibit "S"-shaped behavior with electric field, and was larger near TNI than well above TNI. The results were examined in the context of a model that permits both biaxiality and a field-induced tilt of the molecular director. The results suggest that the primary effect of the electric field is to induce biaxiality, and in consequence suppress the order induced by the surface. No clear indication of a Freedericksz-like transition, either experimental or theoretical, was observed. Appropriate bibliographic citation and notice of the APS copyright must be included- "Kim J.-H., Petschek R.G., Rosenblatt C., Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 60:0.208333333333333, 5600-5606 (1999). Copyright 1999 by the American Physical Society."
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Show moreMeasurements are reported for the polarization in the ordered phase, and for the tilt susceptibility in the 'disordered' smectic A phase, of mixtures of left- and right-handed enantiomers of TFMHPOBC. The tilt susceptibility was found to exhibit a critical exponent γ=1·20±0·05, and both its magnitude and the polarization were found to be nonmonotonic in enantiomeric excess X of S-TFMHPOBC. Their ratio, however, was found to be approximately constant with X. Several possible explanations are examined.
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Show more[No abstract available] Appropriate bibliographic citation and notice of the APS copyright must be included- "Li Z., Petschek R.G., Rosenblatt C., Physical Review Letters 62:13, 1577, 1989. Copyright 1989 by the American Physical Society."
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Show moreResults are reported from a light scattering measurement in the uniaxial nematic phase in the thermotropic liquid crystal octylcyanobiphenyl, a material which does not exhibit a biaxial phase. In addition to a slow Goldstone mode associated with twist fluctuations, a fast mode whose relaxation time is independent of both wave vector and temperature has been observed. The possible origins of this relaxation are discussed. © 1995 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Tripathi S., Zhong H., Petschek R.G., Rosenblatt C., Physical Review E 52:5, 5004-5010 (1995). Copyright 1995 by the American Physical Society."
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Show moreMagnetic and electrical Freedericksz measurements were performed on the second generation monodendritic liquid crystal G2(OH). The deduced elastic constants were found to be exceptionally anisotropic: the splay elastic constant K11 is more than an order of magnitude larger than the bend elastic constant K33, and the twist constant K22 is approximately twice K33. The results are discussed in terms of molecular conformations. European Physical Journal B 5 1998 pp. 251-255 Highly anisotropic elasticity of a dendrimeric liquid crystal Petschek R.G. With kind permission of The European Physical Journal (EPJ).
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Show moreA liquid-crystal light shutter based upon homeotropic orientation has been fabricated, such that no rubbing is required. The device, which is dark in the voltage-off state and transmitting in the voltage-on state, exhibits contrast ratios in excess of 3000:1, with transmission efficiencies of 70% to 95%. Characterization results of one prototype are reported herein. The author is required to post the following copyright notice: "Copyright 1994 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 65:1, 118-120 and may be found at http://link.aip.org/link/doi/10.1063/1.113053.
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Show moreThe coupling between the motion of ionic impurities and the bend-type director distortion in a ferroelectric liquid crystal is examined theoretically. We calculate the relaxation rate of the (fast) director mode to lowest order in the ion concentration. Moreover, we calculate the ratio Kfast(=0)/K(=0), where K() is the amplitude of the temporal autocorrelation function for director fluctuations, is the correlation time, and Kfast() is the corresponding value for the quickly decaying component of this quantity. The ratio, which can be measured in a light-scattering experiment, yields the inverse Debye-Hückel screening length . © 1993 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Lu M.-H., Rosenblatt C., Petschek R.G., Physical Review E 47:2, 1139-1143 (1993). Copyright 1993 by the American Physical Society."
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Show moreAn investigation on light scattering above the nematic - smectic-A phase transition in binary mixtures of bent-core mesogens and calamitic was performed. With dopant concentration X, the regular part of the bend elastic constant decreased strongly. It was found that the divergent part of the bend elastic constant decreased rapidly with X, when close to the nematic - smectic-A phase transition temperature. Appropriate bibliographic citation and notice of the APS copyright must be included- "Dodge M.R., Petschek R.G., Rosenblatt C., Neubert M.E., Walsh M.E., Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 68:3 1, 317031-317036, 2003. Copyright 2003 by the American Physical Society."
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Show moreA tilt of the optic axis linear in transverse electric field was observed in a surface-stabilized chiral nematic liquid crystal. The electroclinic constant ddE was found to exhibit significant pretransitional behavior on approaching the nematic-smectic-A transition temperature from above. A simple theoretical discussion involving coupled order parameters is presented. © 1989 The American Physical Society. Appropriate bibliographic citation and notice of the APS copyright must be included- "Li Z., Petschek R.G., Rosenblatt C., Physical Review Letters 62:7, 796-799, 1989. 1989 by the American Physical Society."
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