共查询到20条相似文献,搜索用时 0 毫秒
1.
I. A. Budagovsky A. S. Zolot’ko V. N. Ochkin M. P. Smayev A. Yu. Bobrovsky V. P. Shibaev M. I. Barnik 《Journal of Experimental and Theoretical Physics》2008,106(1):172-181
The effect of optical orientation in nematic liquid crystals containing small additions of high-molecular compounds, i.e., comb-shaped polymers with light-absorbing azobenzene side fragments, was studied. The effects of light-induced reorientation of the director of nematic liquid crystals caused by light absorption of polymers and a low-molecular compound with a structure similar to side fragments of the polymers were compared in detail. An explanation was proposed for large values of the orientational nonlinearity induced by polymers. 相似文献
2.
A nematic liquid crystal confined between two identical flat solid substrates, with an alternating stripe pattern of planar
and homeotropic anchoring, is studied in the framework of the Frank-Oseen theory. By means of numerical minimization of the
free energy functional we study the effect of the sample thickness D on the location of the phase transition between a uniform alignment, either planar or homeotropic, and a distorted nematic
texture. The solvation force f due to distortions of the nematic director is also studied. It is found that f is always attractive, and for D small compared to the periodicity of the surface structure it exhibits two distinct asymptotic behaviors: f ∼ - D
-1/2 or f ∼ - D
-1, depending on the relation between D and the extrapolation lengths.
Received 12 November 2002 Published online: 16 April 2003 相似文献
3.
E. M. Aver’yanov 《Physics of the Solid State》2014,56(5):1058-1063
The influence of the orientational order of molecules in a nematic liquid crystal on the mean value $\bar \gamma$ and anisotropy Δγ of the molecular polarizability has been studied in the framework of the molecular statistical approach with allowance for the perturbation of the electronic structure of molecules due to the change in the conformation of their aromatic core and intermolecular interactions. Experimental dependences of $\bar \gamma$ and Δγ on the molecular orientational order parameter S have been derived, and their specific features for the known objects have been explained. The possibility of separating the contributions of opposite signs to the dependence Δγ(S) due to the change in the conformation of molecules and intermolecular interactions has been shown using nematic MBBA as an example. 相似文献
4.
S. V. Pasechnik A. P. Krekhov D. V. Shmeleva I. Sh. Nasibullaev V. A. Tsvetkov 《Journal of Experimental and Theoretical Physics》2005,100(4):804-810
The results of studies of orientational dynamics and instability in an MBBA nematic liquid crystal in a decaying Poiseuille flow are considered. The experiments were made on a wedge cell with a gap width varying in a direction perpendicular to the flow. Confining surfaces ensured homeotropic adhesion of the nematic to the surface. Above a certain critical value of the initial pressure drop, a uniform orientational instability is observed, which corresponds to the emergence of the director from the plane of the flow. The dependence of the critical pressure drop on the local thickness of the liquid crystal layer and on the external destabilizing electric field is determined. Simulation of nematodynamics equations is carried out. The results of theoretical calculations are in qualitative and quantitative agreement with the experimental data. 相似文献
5.
We report on the first observation of laser-induced helical structure in the isotropic phase of a nematic liquid crystal. The helical structure was induced by two nearly counter-propagating waves circularly polarized in the same sense. Bragg reflection in the optical tunneling region was studied. We made an extensive investigation on the analogy between Bragg reflection from a cholesteric liquid crystal slab and four-wave mixing. It provides a deeper insight into the physics of the optical properties of cholesteric liquid crystal. 相似文献
6.
M.B. Lacerda Santos M.A. Amato 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):393-400
Using a light-beating technique we have measured the damping time of thermal fluctuations of the nematic director for the
so called cylindrical or calamitic nematic (NC) phase of the lyotropic system K-laurate/decanol/. By varying the scattering angle in suitable geometries, we have been able to estimate the orientational diffusivities associated
to the three pure deformations of splay, twist and bend. A former measurement made in the disk-like ND phase of the same system yielded a large deviation between the splay and twist diffusivities. The effect was then attributed
to induced flows, or backflow, which could be responsible for the reduction of the splay viscosity. In fact, this is the analogous
effect, for disks, to the one recognized since long time ago arriving for rod-like molecules in a classical nematic, though
in this case it is associated with bend deformations. The analogy comes about thanks to the interchange of the role played
by disks and cylinders for, respectively, splay and bend fluctuations.The measurements reported here provide a new test on
the applicability of the backflow model to a nematic system composed of micelles, that is, aggregates made of amphiphilic
(surfactant) molecules, in its cylindrical-like variant, i.e. the NC phase. In addition, the comparative study made here with the previous results existing in the literature for the ND phase, allows us to conjecture on structural issues concerning lyotropic nematics.
Received: 29 April 1998 / Revised: 19 August 1998 / Accepted: 31 August 1998 相似文献
7.
8.
O. L. Antipov S. I. Belyaev A. S. Kuzhelev 《Radiophysics and Quantum Electronics》1995,38(3-4):199-203
Self-pumped phase conjugation of a Nd: YAG laser beam by forward stimulated orientational scattering in a nematic liquid crystal layer with a nonreciprocal feedback loop is investigated. It is found that the threshold of phase-conjugate wave generation is the lowest when the phase shift difference of pumping and scattering waves in the loop is /2.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 304–311, March–April, 1995. 相似文献
9.
The effect of an axial magnetic field on the Poiseuille flow of nematicp-azoxyanisole (PAA) has been computed using the Ericksen-Leslie continuum theory. The apparent viscosity decreases appreciably
in the presence of the magnetic field. Orientation and velocity profiles for different shear rates and magnetic fields are
presented. 相似文献
10.
11.
N. M. Shtykov V. P. Panov M. I. Barnik 《Journal of Experimental and Theoretical Physics》2000,91(1):126-131
Measurements of the temperature dependence of the pyroelectric coefficients in cells with homeotropic and planar boundary conditions were performed in order to study the surface polarization and determine its nature in the isotropic phase of a nematic liquid crystal. Analysis of these data established that the ordering polarization arising as a result of the nonuniformity of the order parameter in the near-boundary region of the liquid crystal and the polar monolayer due to the bifilar properties of the molecules of the liquid crystal at the boundary with the solid wall of the cell are responsible for the surface polarization in the isotropic phase of a nematic liquid crystal. The values of the pyroelectric coefficients of monolayers and the coefficients of the ordering polarization for planar and homeotropic orientations are estimated. 相似文献
12.
13.
The European Physical Journal E - The method of polarization IR-spectroscopy was applied to investigate the change of structure of nematic liquid crystal 5CB interlayers between fluorite plates at... 相似文献
14.
15.
J. Prost 《Physics letters. A》1973,46(3):225-226
We give a simple calculation of the influence of long wavelength fluctuations on the elements of second order tensors describing the properties of nematics, submitted to the action of a magnetic field. A careful analysis of the field dependence of the measured values, should give the validity domain of the Frank elastic theory. 相似文献
16.
We study spontaneous pattern formation in a glass-forming nematic liquid crystal during the magnetically induced dynamic Fréedericksz
transition. Pattern growth rates and wavelengths as functions of the magnetic field are extracted from optical transmission
textures of thin planar cells. The characteristics of the observed stripe pattern can be related to viscoelastic parameters
of the nematic by means of a linear stability analysis of director fluctuation modes. The viscous properties of the material
allow to vary the time scales of the experiment with temperature by orders of magnitude, leaving the spatial structure of
the pattern essentially unchanged. We find that the ratios of shear and rotational viscosity coefficients relevant for the
pattern wavelength selection remain constant in the temperature range investigated, whereas their absolute values change by
almost two orders.
Received 23 November 2001 and Received in final form 19 April 2002 相似文献
17.
The emergence of electric convection in a nematic liquid crystal under the action of a varying electric field is analyzed
in the 1D approximation. A new mode of external field variation with subharmonic oscillations is proposed. The behavior of
several classes of synchronous perturbations and subharmonic oscillations is analyzed; the evolution of the fields of the
director and of the volume charge is studied. Parametric instability regions are specified and the critical frequencies of
transitions between response modes are determined. Stability maps for a nematic liquid crystal are plotted on the frequency-amplitude
plane. 相似文献
18.
é. V. Gevorkyan 《Russian Physics Journal》1981,24(4):343-346
The behavior of nematic liquid crystals in a magnetic field having a static and a rotating component is investigated. Steady-state solutions of the problem (synchronous regime) are obtained, and their stability is analyzed. The influence of the boundary conditions is discussed, along with possible experimental applications. It is shown that the static component of the magnetic field extends the stability range of the synchronous regime.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 57–60, April, 1981. 相似文献
19.
V. K. Abrahamyan N. H. Hakobyan V. M. Aroutiounian N. V. Kamanina H. L. Margaryan D. L. Hovhannisyan D. K. Pokhsraryan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2009,44(6):283-290
Influence of the longitudinal voltage applied along the semiconductor substrate of a planar-oriented liquid crystal cell on
the birefringence of a nematic liquid crystal (NLC) was investigated. It is shown that for a fixed magnitude of the transverse
field the application of a longitudinal voltage creates an additional possibility to control the electro-optically induced
phase incursion of the radiation passing through NLC. Dependence of the phase incursion on the control voltages is obtained.
The results of simulation of the longitudinal voltage effect on the NLC reorientation are described. The obtained results
can be used in development and designing of NLC phase modulators. 相似文献
20.
We study the director field around a spherical particle immersed in a uniformly aligned nematic liquid crystal and assume
that the molecules prefer a homeotropic orientation at the surface of the particle. Three structures are possible: a dipole,
a Saturn-ring, and a surface-ring configuration, which we investigate by numerically minimizing the Frank free energy supplemented
by a magnetic-field and a surface term. In the dipole configuration, which is the absolutely stable structure for micron-size
particles and sufficiently strong surface anchoring, a twist transition is found and analyzed. We show that a transition from
the dipole to the Saturn ring configuration is induced by either decreasing the particle size or by applying a magnetic field.
The effect of metastability and the occurrence of hysteresis in connection with a magnetic field are discussed. The surface-ring
configuration appears when the surface-anchoring strength W is reduced. It is also favored by a large saddle-splay constant K24. A comparison with recent experiments [#!itapdb:Poulin1997!#,#!itapdb:Poulin1998!#] gives a lower bound for W, i.e., for the interface of water and pentylcyanobiphenyl (5CB) in the presence of the surfactant sodium dodecyl sulfate.
Received 2 November 1998 相似文献