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1.
We study stable “bookshelf” smectic-A structures within a very thin plane-parallel cell of thickness L in which the mismatch between surface preferred (d
s) and intrinsic (d0) smectic layer thicknesses occurs. The Landau-Ginzburg approach based on a complex smectic order parameter is used. For a
weak enough smectic positional anchoring strength W smectic layers adopt the modified bookshelf profile. In a thick enough cell with increasing W a lattice of edge dislocations is continuously formed at the confining surfaces and then depinned from them. The structure
with dislocations is formed when the condition d
0/(
d
0/d
s - 1) ∼ 2 is fulfilled, where is the positional surface anchoring extrapolation length. If the cell is thin enough the dislocations formed at opposite
cell plates annihilate and consequently the smectic layers adopt a locked bookshelf structure. This transition is discontinuous
and takes place when d
0/(L
d
0/d
s - 1) ∼ 5 is realized. To observe these transitions in a cell of thickness L∼ 1μm the conditions W∼ 10-6
J/m
2 and
d
0/d
s - 1∼ 5 . 10-4 have to be fulfilled. All the three qualitatively different structures coexist at the triple point.
Received 21 February 2002 相似文献
2.
P. Cluzeau P. Barois H.T. Nguyen C. Destrade 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):73-82
We report X-ray diffraction experiments performed on an antiferroelectric compound exhibiting a very rich polymorphism (). The structural study of the unknown phases only allows us to exclude some phenomenological models. The use of oriented
planar samples prepared between solid glass plates generate by cooling from the phase a chevron structure of tilted layers already well characterized for the phase. The extensive analysis of the evolution of the chevron structure through the numerous smectic-smectic phase transitions
provides some original information in three distinct areas: fundamental data on the important physical parameters in the chevron
structure formation, detection of the smectic-smectic phases transition by small change of the chevron structure, and information
on the local molecular order induced by the alignment layer (interaction with a rubbed polymer).
Received: 13 November 1996 / Received in final form: 19 January 1997 / Accepted: 30 January 1998 相似文献
3.
The effect of an external electric field on the local layer structure is investigated in the SmC*
A, SmC*
FI and SmC* phases using X-ray diffraction. X-ray scattering and spontaneous polarization measurements are performed under several increasing
(and decreasing) steps of AC applied voltage. The effects of the electric field differ significantly from one phase to the
other. The chevron-to-bookshelf transition occurs abruptly at a high field value in the SmC*
A phase whereas layer deformations are more progressive and occur at lower field values in the other phases. Comparison of
the different behaviours suggests that the destruction of the chevron structure is mainly affected by the local molecular
order.
Received 16 July 2001 and Received in final form 7 December 2001 相似文献
4.
A. V. Emelyanenko 《The European physical journal. E, Soft matter》2009,28(4):441-455
The fundamental theoretical approach derived in A.V. Emelyanenko et al., Phys. Rev. E 74, 011705 (2006) is complemented by a consideration of the influence of the homogeneous electric field on Sm- C
A
* , biaxial intermediate phases, and Sm-C
* . The crucial role of the induced polarization is investigated for the first time. The evolution of any tilted smectic phase
in the electric field is found to meet the two thresholds. The first threshold corresponds to the unwinding process, and the
second one corresponds to the phase transition into the bi-domain structure of Sm-C
* , where the tilt plane has some contribution either along or against the electric field, while the average direction may
still be perpendicular to the electric field. The tilt plane in the monodomain (conventional) structure preceding the second
threshold is the same in every unwound phase, and is perpendicular to the electric field. No 3D distortion in Sm- C
A
* is predicted on application of the electric field. The entire electric-field-temperature phase diagrams including the possibility
of existence of the maximal number of tilted smectic phases are plotted and compared with the experimental ones. The numerical
calculations in the framework of this fundamental study are done with help of AFLC Phase Diagram Plotter software developed
by the author and available at his web page. 相似文献
5.
Dierking I Glusen B Lagerwall ST Ober CK 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(2):1593-1598
We have investigated the phenomenon of field-induced smectic layer instability, as monitored by synchrotron x-ray scattering. This instability means that, upon application of time-asymmetric electric fields to chiral smectics, the layer direction seems to "rotate" locally around an axis given by the direction of the applied field. For moderate values of field amplitude and asymmetry, domains with a favored layer inclination grow at the expense of unfavored ones, while larger fields and asymmetries generally lead to a chaotic flow behavior. At moderate amplitudes, we have followed the process of the horizontal layer folding (or horizontal chevron domain formation) and the smectic C* layer reorientation of ferroelectric liquid crystals by applying symmetric and asymmetric wave forms, respectively, and performing time resolved x-ray measurements. The studies unambiguously show the formation of a horizontal (in-plane, i.e., in a plane parallel to the cell substrates) chevron domain structure from a nonoriented sample by application of a symmetric electric field of sufficient amplitude. It is then demonstrated that a transition from the horizontal chevron domain structure to an in-plane uniform smectic layer direction takes place on application of asymmetric electric wave forms. Reversal of the field asymmetry reverses the inclination direction and selects the other layer normal direction as the uniform end state. The in-plane smectic layer reorientation process is followed here as it evolves, and analyzed directly by means of x-ray scattering. 相似文献
6.
V. K. Dolganov E. I. Kats S. V. Malinin 《Journal of Experimental and Theoretical Physics》2001,93(3):533-541
Experimental data on the optical reflectance of free-standing smectic C films were analyzed within the framework of a phenomenological Landau approach. At a certain temperature T 0N (determined from experimental data), which exceeds the known temperature T c of the volume phase transition from smectic A to smectic C state, a surface phase transition takes place whereby molecules in the surface layer become sloped relative to the normal of the smectic layers. The transition temperatures T 0N s,a for N-layer films possessing synclinic (symmetric) and anticlinic (antisymmetric) textures of the order parameter (tilt angle θ) were determined. A comparison of the theoretical and experimental data allowed all parameters of the model to be determined (including critical indices of the correlation length and the surface order parameter). Three possible models of the transition from the state with transverse polarization (perpendicular to the molecular tilt plane) to the state with longitudinal polarization (parallel to this plane) are analyzed. The transition takes place at low (°–°) values of the order parameter θ in the middle layer of the film. 相似文献
7.
Within the framework of Landau-de-Gennes formulation, we analyse the effect of pressure on electric-field-induced phase transitions
in a liquid crystal which shows spontaneously an isotropic-smectic A transition. Inferring from the experimental pressure
dependences on the layer spacing in smectic A phase, as well as the nematic-smectic A metastable temperature T*AN, we incorporated the pressure dependence in the free energy through (the surface energy term) and the coupling between the
quadrupolar nematic ordering Qij and the smectic order parameter ψ. From the S-T phase diagram, we found that the stability of field-induced nematic phase increases with pressure, whereas the discontinuity
of the transition decreases. Also, the region where paranematic phase transits directly to smectic A phase increases with
pressure. 相似文献
8.
W.Z. Wang K.L. Yao 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):437-441
A ferrimagnetic polymer with m-phenylene skeleton as coupling unit is studied with the Hubbard model in the self-consistent mean-field theory. The ferrimagnetic
ground state with a total spin S = 1 per unit cell is obtained and originates from the antiferromagnetic correlations between the nearest neighbors. If the
on-site electron-electron repulsions at the radical sites and at the phenylene ring sites are different, the gap in energy
band structure may disappear and the ferrimagnetic ground state becomes unstable. The charge density and spin density can
transfer between the radical sites and the phenylene ring sites due to the competition between the hopping integral and the
on-site repulsion at different sites.
Received 15 July 2002 Published online 31 December 2002 相似文献
9.
The positron lifetime and DSC measerments for EBBA and DOBAMBC have been made with heating and cooling clycles. The experimental results show that a shorter lifetime (1) is essentially independent of temperature while the longer lifetime (2) and the intensity (I
2) change abruptly double or triple with temperature. Consequently, the EBBA has only nematic phases while the DOBAMBC has two liquid-crystalline phases (smectic C* and smectic A) with transition temperatures as follows: for EBBA, solid nematic (304.5 K), nematic isotropic (356.5 K), isotropic nematic (356.5 K), nematic solid (301 K); and for DOBAMBC, solid smectic C* (346 K), smectic C* smectic A (357.5 K), smectic A isotropic (389 K). These critical temperatures are in accordance with the transition temperatures measured by DSC. In addition, the difference in the solid-nematic transition temperature in the heating and cooling cycles was also observed. A discussion about the correlation of the observed changes in lifetime (2) with the changes in molecular orientational order (S) and dielectric anisotropy () is presented. 相似文献
10.
The orientational properties of a ferroelectric smectic C* that forms a chevron structure in a bounded cell in a weak electric field have been described theoretically. Two spatial
distributions of the director that transform into each other with a change in the field direction to the opposite direction
have been calculated. It has been shown that the hysteresis should be observed in this transition, and the threshold field
that results in the director reorientation with a change in the field direction has been estimated. 相似文献
11.
Yu.P. Gangrsky V.D. Karaivanov B.N. Markov S.G. Zemlyanoi Tz.T. Kokalova K.P. Marinova E. Stachowska J. Dembczynski J. Ruczkowski B. Arcimowicz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):341-345
The laser-induced resonance fluorescence in an atomic beam was used in order to measure the hyperfine splitting of the 4f
7 6s
2
and 4f7 6s6p
levels in 151,153,155Eu isotopes. The hfs constants A and B of the unstable 155Eu were determined for the first time: MHz, MHz and MHz. With these data and after corrections for second-order hyperfine structure perturbations the nuclear moments of 155Eu were deduced: n.m. and b. In addition new and more precise values of the hfs constants of the excited state for the stable 151,153Eu were obtained. They are as follows: MHz, MHz and MHz, MHz. The hyperfine anomalies % and % were extracted from the corrected hfs constants.
Received 28 July 1999 and Received in final form 14 January 2000 相似文献
12.
A. Hazareesing J.-P. Bouchaud 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):713-724
We reconsider the problem of the static thermal roughening of an elastic manifold at the critical dimension d=2 in a periodic potential, using a perturbative Functional Renormalization Group approach. Our aim is to describe the effective
potential seen by the manifold below the roughening temperature on large length scales. We obtain analytically a flow equation
for the potential and surface tension of the manifold, valid for low temperatures. On a length scale L, the renormalized potential is made up of a succession of quasi parabolic wells, matching onto one another in a singular
region of width for large L. For strong periodic potential, the perturbation theory breaks down, and we argue, based on a variational calculation, that
the transition becomes first order. We also obtain numerically the step energy as a function of temperature, and relate our
results to the existing experimental data on 4He. Finally, we examine the case of a non local elasticity which is realized physically for the contact line.
Received 16 April 1999 and Received in final form 11 October 1999 相似文献
13.
We present experimental data on the apparent layer complex rigidity of the smectic A, C, B phases of 40 P90B versus temperature at a fixed frequency of 50 Hz. Across the nematic → smectic A and smectic A → smectic C second order transitions, the modulus of the rigidity coefficient becomes very weak, and its phase undergoes a rapid variation of π, in a range of about 100 mK. At the first order smectic C → smectic transition, a corresponding discontinuity is observed. This behavior is tentatively explained in term of coupling of the nematic director (or defects) with the shear flow associated with the compression, and an associated viscoelastic relaxation. 相似文献
14.
We study the nature of the smectic–isotropic phase transition using a mobile 6-state Potts model. Each Potts state represents a molecular orientation. We show that with the choice of an appropriate microscopic Hamiltonian describing the interaction between individual molecules modeled by a mobile 6-state Potts spins, we observe the smectic phase dynamically formed when we cool the molecules from the isotropic phase to low temperatures (T). In order to elucidate the order of the transition and the low-T properties, we use the high-performance Wang–Landau flat energy-histogram technique. We show that the smectic phase goes to the liquid (isotropic) phase by melting/evaporating layer by layer starting from the film surface with increasing T. At a higher T, the whole remaining layers become orientationally disordered. The melting of each layer is characterized by a peak of the specific heat. Such a succession of partial transitions cannot be seen by the Metropolis algorithm. The successive layer meltings/evaporations at low T are found to have a first-order character by examining the energy histogram. These results are in agreement with experiments performed on some smectic liquid crystals. 相似文献
15.
Eric Grelet Peter J. Collings Min-Hui Li Huu-Tinh Nguyen 《The European physical journal. E, Soft matter》2001,6(2):157-161
Optical activity measurements have been performed on the smectic blue phases ( BP
Sm), which are a new kind of chiral liquid crystal. BP
Sm exhibit both three-dimensional orientational order, like the classical blue phases, and smectic positional order. Thus, they
can be viewed as the three-dimensional counterpart of the twist grain boundary phases. A comparison with the optical activity
of the classical blue phases is carried out, and an estimation of the BP
Sm lattice parameter is reported for the first time.
Received 25 May 2001 相似文献
16.
L. V. Mirantsev 《Physics of the Solid State》1999,41(10):1729-1735
A theoretical study is reported of fluctuations in smectic layer displacements and of the correlations between them in free-standing
smectic-A films formed of liquid-crystal compounds with smectic-A-isotropic liquid (Sm-A-I) and Sm-A-nematic (Sm-A-N) bulk phase transitions. The study took into account the dependence of the elastic constants for bending, K, and tension (compression), B, of smectic layers on distance to the free film surfaces. The calculations are compared with the results obtained within
Hołyst’s model for spatially uniform, free-standing smectic-A films. It has been established that, below the temperature at which smectic order in the bulk of a liquid crystal disappears,
taking into account the profiles of the elastic moduli K and B does not produce noticeable differences from this model. However, at temperatures considerably above the Sm-A-I and Sm-A-N phase transitions, their inclusion results in considerable discrepancies from the predictions of Hołyst’s model.
Fiz. Tverd. Tela (St. Petersburg) 41, 1882–1889 (October 1999) 相似文献
17.
A. Benyoussef D. Dohmi A. El Kenz L. Peliti 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):503-510
Using a replica formalism, a generalization of a recent mean field model corresponding to the observed wrinkling transition
in randomly polymerized membranes is presented. In this model we study the effects of global fluctuations of the surface normals
to the flat membrane, which can be introduced by a random local field. In absence of these global fluctuations, we show that,
the model exhibits both continuous and discontinuous transitions between flat and wrinkled phases, contrary to what has been
predicted by Bensimon et al. and Attal et al. Phase diagrams both in replica symmetry and in breaking of replica symmetry in sense of Almeida and Thouless are given. We
have also investigated the effects of global fluctuations on the replica symmetry phase diagram. We show that, the wrinkled
phase is favored and the flat phase is unstable. For large global fluctuations, the transition between wrinkled and flat phases
becomes first order.
Received: 3 December 1997 / Revised: 31 March 1998 / Accepted: 3 August 1998 相似文献
18.
19.
J.L. Meunier A. Morel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):341-352
For the first order transition of the Ising model below , Isakov has proven that the free energy possesses an essential singularity in the applied field. Such a singularity in the
control parameter, anticipated by condensation theory, is believed to be a generic feature of first order transitions, but
too weak to be observable. We study these issues for the temperature driven transition of the q states 2D Potts model at . Adapting the droplet model to this case, we relate its parameters to the critical properties at and confront the free energy to the many informations brought by previous works. The essential singularity predicted at the
transition temperature leads to observable effects in numerical data. On a finite lattice, a metastability domain of temperatures
is identified, which shrinks to zero in the thermodynamical limit.
Received 30 March 1999 相似文献
20.
We introduce a solid-on-solid growth process which evolves by random deposition of dimers, surface diffusion, and evaporation
of monomers from the edges of plateaus. It is shown that the model exhibits a robust transition from a smooth to a rough phase.
The roughening transition is driven by an absorbing phase transition at the bottom layer of the interface, which displays
the same type of critical behavior as the pair contact process with diffusion 2A↦3A, 2A↦.
Received 14 October 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: Haye.Hinrichsen@physik.uni-wuppertal.de 相似文献