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1.
Self-organization of cholesteric and nematic droplets in smectic free-standing films is investigated. Strong tangential anchoring
at the droplet boundary leads to nucleation of a topological defect and formation of a topological dipole from the droplet
and the defect. The interaction between droplets results in assembly of the droplets in dimers and line chains. Topological
dipoles of the droplet-defect pairs can be oriented in dimers with polar (ferroelectric) and nonpolar (antiferroelectric)
ordering. In this paper we found novel dimer structures formed by droplets with different handedness of the c-director field near the droplets. Depending on the relative magnitude of the droplet dipoles the resulting structure may
be dipolar or quadrupolar. Formation of antiferroelectric dimers is discussed on the basis of electromagnetic analogy. 相似文献
2.
H. Stark J. Stelzer R. Bernhard 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):515-523
Recently, it was observed that water droplets suspended in a nematic liquid crystal form linear chains [Poulin et al., Science 275, 1770 (1997)]. The chaining occurs, e.g., in a large nematic drop with homeotropic boundary conditions at all the surfaces. Between each pair of water droplets a
point defect in the liquid crystalline order was found in accordance with topological constraints. This point defect causes
a repulsion between the water droplets. In our numerical investigation we limit ourselves to a chain of two droplets. For
such a complex geometry we use the method of finite elements to minimize the Frank free energy. We confirm an experimental
observation that the distance d of the point defect from the surface of a water droplet scales with the radius r of the droplet like .When the water droplets are moved apart, we find that the point defect does not stay in the middle between the droplets,
but rather forms a dipole with one of them. This confirms a theoretical model for the chaining. Analogies to a second order
phase transition are drawn. We also find the dipole when one water droplet is suspended in a bipolar nematic drop with two
boojums, i.e., surface defects at the outer boundary. Finally, we present a configuration where two droplets repel each other without a
defect between them.
Received 11 December 1998 相似文献
3.
Dolganov PV Nguyen HT Joly G Dolganov VK Cluzeau P 《The European physical journal. E, Soft matter》2008,25(1):31-37
New mechanisms of droplet nucleation and self-organization in ferroelectric membranes are described. The droplets may be accompanied
by different number of topological defects (zero, one, two) whose location may be on the droplet boundary or in the membrane.
Nucleation and self-organization of droplets with total topological charge S = 0 , S = + 1 and S = - 1 were investigated. We found that an S = - 1 topological defect may be the center of both droplet nucleation and chain formation. This mechanism of chaining drastically
differs from the droplet self-organization described earlier which is realized by attraction of droplet-defect pairs. Our
observations demonstrate new possibilities for manipulating the inclusions and their self-organization in smectic membranes. 相似文献
4.
The formation of unusual chain structures and clusters of particles with the mixed dipole–quadrupole interaction has been found in smectic nanofilms. Unlike topological dipoles and quadrupoles, the interaction between which leads to the formation of structures with finite interparticle distances, the particles with the mixed interaction touch each other and form stable chains and two-dimensional clusters. The orientation of particles in chains is intermediate between dipole and quadrupole chains. The variation of the interparticle distance and orientation of chains is explained qualitatively on the basis of the calculation of the с-director (field lines) near particles and the mutual arrangement of particles providing the minimum distortion of field lines. 相似文献
5.
Wang Haiyan Liu Riping Ma Mingzhen Jing Qin Li Gong Sun Liling Wang Wenkui 《中国科学G辑(英文版)》2005,48(2):658-666
Solidification of 0.1–1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and
SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet
diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like
to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different
cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology
changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the
microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the
larger cooling rate on the surface than at the center. 相似文献
6.
The morphology of magnetic fluid droplets on magnetic thin film dots is studied experimentally, including the aspect ratio and the contact angle variation of the droplets. Under a uniform external magnetic field, the droplet's aspect ratio increases with the external field and with the diameter of the magnetic dot due to the concentrated magnetic flux inside the magnetic fluid droplet. Similar to the electrical wetting phenomenon, the induced magnetic dipoles in the magnetic film and in the magnetic fluid near the solid–liquid interface change the solid–liquid interfacial tension, and in consequence reduce the apparent contact angle of the magnetic fluid droplet. 相似文献
7.
P. V. Dolganov N. S. Shuravin V. K. Dolganov A. Fukuda 《Journal of Experimental and Theoretical Physics》2017,125(4):709-713
Heterochiral islands, in which topological dipoles are oppositely directed, are observed in freestanding antiferroelectric (SmC A *) films. The topological dipoles in films with a transverse electric polarization and a planar molecule orientation at island boundaries are coplanar with an electric field. The topological dipoles in films with a longitudinal polarization and a planar orientation at island boundaries are perpendicular to an electric field. For a radial director orientation at island boundaries, the topological dipoles in films with a longitudinal polarization are coplanar with a field. Changing the orientation of an electric field, we can control the position of a topological defect at an island boundary and the orientation of a topological dipole. Heterochiral islands can form dimers with an anomalously small interisland distance. 相似文献
8.
Tixier T Heppenstall-Butler M Terentjev EM 《The European physical journal. E, Soft matter》2005,18(4):417-423
We studied a new kind of W/O emulsions based on a
lyotropic liquid crystal as the aqueous droplet phase. The
cholesteric phase, a solution hydroxypropyl cellulose in water was
dispersed in the continuous oil matrix, paraffin oil or heptane.
We made a specific choice of surfactant in order to impose
director anchoring conditions at the oil-water interface and
orient the liquid crystal inside the droplet. The strong anchoring
conditions resulted in a topological defect inside the droplets of
size above the critical value R*. The defect elastic energy
creates a barrier against droplet coalescence, the effect of
topological size selection. We have studied the orientation of the
director inside the droplets and their size distribution. 相似文献
9.
The structures of zigzag-zigzag, armchair-zigzag, zigzag-chiral, armchair-armchair, armchair-chiral, and chiral-chiral pair
connections produced by single-walled carbon nanotubes 1.5–5.0 diameter with the use of the combined 5–7 and 4–8 topological
defects have been calculated by molecular mechanics methods. It has been established that the use of the combined 5–7 topological
defect makes it possible to produce connections between pairs of single-walled carbon nanotubes with any conductivities, chiralities,
and diameters, whereas the use of the combined 4–8 topological defect provides a means for forming connections between nanotubes
only with the same type of conductivity. The angles between the axes of nanotubes connected by the combined 5–7 and 4–8 topological
defects lie in the ranges 145°–180° and 112°–178°, respectively. It has been revealed that there are correlations between
structural parameters of the connections and the relative arrangement of the simple topological defects in the combined topological
defects. 相似文献
10.
M. Salis 《Il Nuovo Cimento D》1995,17(6):649-651
Summary Experiments on the thermoluminescent emission of samples of natural α-spodumene show the presence of a large density of defects.
Comparison with defect density in synthetic β-spodumene indicates that in natural α-spodumene defects are not in thermodynamic
equilibrium. 相似文献
11.
Nych AB Ognysta UM Pergamenshchik VM Lev BI Nazarenko VG Musevic I Skarabot M Lavrentovich OD 《Physical review letters》2007,98(5):057801
Glycerol droplets at a nematic-liquid-crystal-air interface form two different lattices--hexagonal and dense quasihexagonal--which are separated by the energy barrier and can coexist. Director distortions around each droplet form an elastic dipole. The first order transition between the two lattices is driven by a reduction of the dipole-dipole repulsion through reorientation of these dipoles. The elastic-capillary attraction is essential for the both lattices. The effect has a many-body origin. 相似文献
12.
13.
P. Patrício M. Tasinkevych M.M. Telo da Gama 《The European physical journal. E, Soft matter》2002,7(2):117-122
We use a two-dimensional (2D) elastic free energy to calculate the effective interaction between two circular disks immersed
in smectic-C films. For strong homeotropic anchoring, the distortion of the director field caused by the disks generates topological
defects that induce an effective interaction between the disks. We use finite elements, with adaptive meshing, to minimize
the 2D elastic free energy. The method is shown to be accurate and efficient for inhomogeneities on the length scales set
by the disks and the defects, that differ by up to 3 orders of magnitude. We compute the effective interaction between two
disk-defect pairs in a simple (linear) configuration. For large disk separations, D, the elastic free energy scales as ∼D
-2, confirming the dipolar character of the long-range effective interaction. For small D the energy exhibits a pronounced minimum. The lowest energy corresponds to a symmetrical configuration of the disk-defect
pairs, with the inner defect at the mid-point between the disks. The disks are separated by a distance that is twice the distance
of the outer defect from the nearest disk. The latter is identical to the equilibrium distance of a defect nucleated by an
isolated disk.
Received 26 October 2001 and Received in final form 14 December 2001 相似文献
14.
The formation of droplets (or breathers) of vortex matter in Bi(2)Sr(2)CaCu(2)O(8) crystals pumped by the low-frequency ac magnetic field is observed by magneto-optic imaging. The droplets nucleate at the points of crossing the planar defects. The magnetic flux in the droplet and the droplet size increase with time. When the flux in the droplet exceeds a critical value, the droplet shifts along the defect to the sample bulk and a new droplet with the opposite flux direction starts to nucleate at the same point. As a result, a beadlike structure of the droplets arises along the defect. A possible explanation of the phenomenon is proposed. 相似文献
15.
S. A. Gusev L. A. Mazo M. Nefedov Yu. N. Nozdrin M. V. Sapozhnikov L. V. Sukhodoev A. A. Fraerman 《JETP Letters》1998,68(6):509-513
Collective effects arising in a two-dimensional lattice of nanosize magnetic particles as a result of the dipole interparticle
interaction are investigated by Hall magnetometry. The experimental system consists of 105 permalloy particles having a diameter of ∼40 nm and a height of ∼40 nm and forming a lattice with a rectangular unit cell
(90 nm×180 nm). We attribute the characteristic features observed in the magnetization curves to quasi-one-dimensionality
of the experimental lattice of particles and to the formation of solitons in chains of dipoles.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 475–479 (25 September 1998) 相似文献
16.
O. A. Skaldin V. A. Delev E. S. Shikhovtseva E. S. Batyrshin Yu. A. Lebedev 《JETP Letters》2011,93(7):388-393
The dynamics of nonsingular defects has been studied experimentally and theoretically in the periodic roll structures arising
at electroconvection in nematic liquid crystals twisted by π/2. The presence of an axial component of the velocity of the
hydrodynamic flow with the opposite direction in the neighboring rolls is characteristic of roll structures in twisted nematics.
The quantitative estimates of the critical frequency of the oscillations of structural defects have been obtained on the basis
of the nonlinear equation of motion for the roll displacement. It has been found that the periodic creation and annihilation
of a pair of edge dislocations with the topological indices +1 and −1 occur in the process of oscillations of a defect with
a nonsingular nucleus. It has been demonstrated that oscillating defects with zero topological indices correspond to the solution
of the sine-Gordon equation in the form of standing breathers. 相似文献
17.
The Kirkwood-Frohlich correlation factor (g), Eyring’s parametersG and G* and the dipolar excess free energies of dilute solutions of formamide, acetamide,N-methyl acetamide,N,N-dimethyl formamide andN,N-dimethyl acetamide in 1,4-dioxan/benzene were obtained from a measurement of their static dielectric permittivities at 308
K. The fluid structure of these amides is discussed. Both in formamide and acetamide a dimeric linear chain with the individual
dipoles more or less parallely oriented is preferred. InN-methyl acetamide, the antiparallel orientation of dipoles at lower concentrations turns into a parallel orientation with
increase of concentration. In tertiary amides, with increase of concentration, parallel orientation of dipoles with global
value ofg tending to unity is observed. The dipolar excess free energy of mixing in a given solvent is of the order primary amide >
secondary amide > tertiary amide. 相似文献
18.
We consider the radiation from nonoscillating dipoles traveling with constant velocity directed parallel or antiparallel to
the velocity of a homogeneous transparent moving medium. It is assumed that the medium in its rest frame is isotropic and
has no spatial dispersion. We obtain expressions for the radiative energy losses and estimate the polarization energy losses
of electric and magnetic dipoles of different orientations. In particular, it is shown that the energy loss of a source is
negative if it moves in the direction of the medium motion and the source velocity is less than the medium velocity. Estimates
for the energy losses of dipoles in the cases of an electron beam and a flow of a weakly dispersive medium are given.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 6, pp. 502–512, June 2006. 相似文献
19.
Shunsuke Suzuki Akira Nakajima Kouichi Tanaka Ayako Hashimoto Yoshikazu Kameshima Kiyoshi Okada 《Applied Surface Science》2008,254(6):1797-1805
We prepared line-patterned hydrophobic surfaces using fluoroalkylsilane (FAS) and octadecyltrimethoxysilane (ODS) then investigated the effect of line direction on sliding behavior of water droplets by direct observation of the actual droplet motion during sliding. Water droplets slide down with a periodic large deformation of the contact line and sliding velocity fluctuation that occurred when they crossed over the 500-μm ODS line regions in FAS regions on a Si surface tilted at 35°. These behaviors are less marked for motion on a 100-μm line surface, or on lines oriented parallel to the slope direction. Smaller droplets slide down with greater displacement in the line direction on 500-μm line patterning when the lines were rotated at 13° in-plane for the slope direction. This sliding behavior depended on the droplet size and rotation angle, and is accountable by the balance between gravitational and retentive forces. 相似文献
20.
T. Dobrowolski 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):269-271
The production of topological defects during a quench in a φ4 model is investigated. The influence of a spatially correlated noise on defect production in two and three dimensions is
demonstrated.
Received 28 August 2001 / Received in final form 11 February 2002 Published online 2 October 2002
RID="a"
ID="a"Paper supported in part by ESF “COSLAB” Programme
RID="b"
ID="b"e-mail: sfdobrow@kinga.cyf-kr.edu.pl 相似文献