1,506 research outputs found
Comment on "Freezing by heating in a driven mesoscopic system"
We point out that the phenomenon ``heating by freezing'' discovered in
nonequilibrium simulations by Helbing, et al. (PRL 84, 1240 (2000)) extends to
equilibrium systems as well. We argue that such reentrant fluctuation-driven
freezing can, for example, be realized in two-dimensional colloidal systems
subjected to a one-dimensional periodic potential.Comment: 4 RevTeX pg
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Brillouin Scattering from Smectic Liquid Crystals
Brillouin-scattering results are reported for monodomain samples of -methyl butyl p [(p-methoxy benzylidine)amino] cinnamate in both the smectic-A and -B phases. For both phases theoretical predictions are confirmed concerning the number and polarizations of the propagating hypersonic waves. We report quantitative measurements of various thermodynamic derivatives, including the coupling between density and smectic-layer spacing. We discuss preliminary evidence concerning one model of the smectic-B phase.Engineering and Applied Science
Dielectric spectroscopy of ferroelectric nematic liquid crystals: Measuring the capacitance of insulating interfacial layers
Numerous measurements of the dielectric constant of the recently
discovered ferroelectric nematic () liquid crystal (LC) phase report
extraordinarily large values of (up to ~30,000). We show that
what is in fact being measured in such experiments is the high capacitance of
the non-ferroelectric, interfacial, insulating layers of nanoscale thickness
that bound the material in typical cells.
We analyze a parallel-plate cell filled with material of
high-polarization , oriented parallel to the plates at zero applied
voltage. Minimization of the dominant electrostatic energy renders
spatially uniform and orients it to make the electric field in the as
small as possible, a condition under which the voltage applied to the cell
appears almost entirely across the high-capacity interfacial layers. This
coupling of orientation and charge creates a combined polarization-external
capacitance (PCG) Goldstone reorientation mode requiring applied voltages
orders of magnitude smaller than that of the layer alone to effectively
transport charge across the layer. The layer acts as a low-value
resistor and the interfacial capacitors as reversible energy storage
reservoirs, lowering the restoring force (mass) of the PCG mode and producing
strong reactive dielectric behavior. Analysis of data from several experiments
on ferroelectric liquid crystals (chiral smectics C, bent-core smectics, and
the phase supports the PCG model, showing deriving that deriving
dielectric constants from electrical impedance measurements of
high-polarization ferroelectric LCs, without properly accounting for the
self-screening effects of polarization charge and the capacitive contributions
of interfacial layers, can result in overestimation of the
values of the LC by many orders of magnitude.Comment: 26 pages of text, 10 figures, 49 references (40 pages total
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Backbone-free duplex-stacked monomer nucleic acids exhibiting Watson-Crick selectivity.
We demonstrate that nucleic acid (NA) mononucleotide triphosphates (dNTPs and rNTPs), at sufficiently high concentration and low temperature in aqueous solution, can exhibit a phase transition in which chromonic columnar liquid crystal ordering spontaneously appears. Remarkably, this polymer-free state exhibits, in a self-assembly of NA monomers, the key structural elements of biological nucleic acids, including: long-ranged duplex stacking of base pairs, complementarity-dependent partitioning of molecules, and Watson-Crick selectivity, such that, among all solutions of adenosine, cytosine, guanine, and thymine NTPs and their binary mixtures, duplex columnar ordering is most stable in the A-T and C-G combinations
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Polarized Raman Scattering Studies of Orientational Order in Uniaxial Liquid Crystalline Phases
The measurement of vibrational Raman depolarization ratios has been used to study molecular orientational order in uniaxial single domain nematic and smectic liquid crystal samples. This technique is demonstrated to obtain the same microscopic order parameter , where is the angle between a molecular long axis and the uniaxial direction, as other existing methods. In addition, the next higher moment of the orientational distribution function has been measured for the first time. The physical basis, theoretical apparatus, and experimental methods necessary for the application of this technique are thoroughly detailed in this paper. Measurements are presented of the temperature dependence of and of N‐(p'‐butoxybenzylidene)‐p‐cyanoaniline (BBCA) dissolved in N‐(p'‐methoxybenzylidene)‐p‐cyanoaniline (MBBA) and of pure MBBA in the isotropic and nematic phases, and in the isotropic, nematic, smectic A, and smectic B phases of N‐(p'‐butoxybenzylidene)‐p‐n‐octylaniline (40.8). In the nematic phases the new quantitative information marks significant discrepancies with existing theories of nematic ordering. In the smectic phases the results show unambiguously the anticipated high degree of molecular orientational order.Engineering and Applied Science
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