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1.
B. Yahiaoui A. Gharbi M. Kléman J. Malthête 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):99-110
Electron microscopy observations of replicas of freeze-fractured samples of two columnar hexagonal phases of different nature (a lyotropic one, the inverse AOT in water; a thermotropic one, ) yield very different results: most defects at microscopic scales are screw dislocations in the lyotropic phase, longitudinal
edge dislocations in the thermotropic phase. A possible way to interpret these differences is as follows: in the lyotropic
the Lamé coefficients and μ and the bend modulus K3 would not display any anomaly compared to expected values; in the thermotropic the shear modulus μ would be ten times smaller
than the compressibility modulus , while K3 would still be comparable to (but larger than) the bend modulus of a small molecules liquid crystal. We present an elementary
theoretical model of the latter case which could explain the anomalous measurements of K3 and of the longitudinal compressibility (Ref. [#!ref10!#]) without contradicting more recent measurements of (Refs. [#!ref17!#,#!ref22!#]). Essentially, the hexagonal phase would be a phase with defects (longitudinal dislocations) akin to an hexatic phase but with some differences.
Re?u : 26 mai 1997 / Révisé : 20 Janvier 1998 /
Accepté : 27 avril 1998 相似文献
2.
F. Hardouin M.F. Achard J.-I. Jin Y.-K. Yun S.-J. Chung 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):47-56
Systematic physical chemistry studies are in progress concerning the occurrence of incommensurate low ordered smectic phases
in non-symmetric dimesogens varying molecular parameters from the standard compound KI-5. In the present study, the selected
molecules possess the same spacer length and the same cholesteryl unit. By means of X-ray diffraction on orientated samples,
commensurate phases, incommensurate fluid smectics and two-dimensional ones are clearly evidenced depending both on temperature
and molecular parameters. So these dimesogenic compounds respond to the frustration connected to the competition between two
incommensurate lengths with the formation either of an incommensurate phase or of a two-dimensional modulated phase. A new topology in a phase diagram results from this competition in a binary system
composed of two homologous dimesogens.
Received: 26 June 1997 / Revised: 7 October 1997 / Accepted: 29 October 1997 相似文献
3.
Several new kinds of smectic-C twist grain boundary phases (TGBC) have been observed during the last few years. These pure
compounds or mixtures exhibit unusual textures with polygonal lattices (square or hexagonal grids) in the plane normal to
the TGB helix. The structure of these new phases seems to be complex and different from reported and predicted TGBC phases.
In this article, we review the main results obtained on these different new phases, and we propose new TGBC structures based
on the well-known splayed polarization --twisted director structures adopted by chiral smectic-C's in planar aligned (bookshelf)
cells. The observed square or hexagonal lattices are made of superimposed pairs of unwinding lines due to the suppression
of the helix within smectic-C blocks by the grain boundaries (unwinding walls). A lattice-free TGBC occurs if the helix within
smectic-C blocks is suppressed completely.
Received 15 March 2001 相似文献
4.
A. B. D. Brown C. Ferrero T. Narayanan A. R. Rennie 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):481-489
The structure and phase behaviour of a colloidal dispersion of plate-like particles are described. The plates are nickel (II)
hydroxide and have short-range, repulsive interactions and a low polydispersity. As the concentration of the plates is increased,
an equilibrium phase separation between a columnar phase and a less ordered phase is observed. Complementary measurements
using small-angle neutron and small-angle X-ray scattering have been used to distinguish the columnar phase from other possible
ordered structures. Previously isotropic-nematic phase transitions have been observed [#!ref1!#], however this dispersion
forms the more highly ordered columnar phase, due to the aspect ratio and the low polydispersity of the plate-like particles.
The concentration at which phase separation occurs, increases as the range of the particle interactions is reduced. This system
provides an interesting model for comparison with theory and calculations of structures in liquid crystal and mesophase in
which the particle interactions can be altered.
Received 24 February 1999 相似文献
5.
P. Barois F. Heidelbach L. Navailles H. T. Nguyen M. Nobili M. Petit R. Pindak C. Riekel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):455-462
We report the first X-ray scattering investigation of spatial variations of the q-fold quasicrystalline symmetry (so-called commensurability) of well-aligned samples. A spatial resolution of was achieved using the ESRF microfocus beamline. The liquid crystal samples, contained between glass plates which were either
parallel or in a wedge geometry, were scanned in order (i) to probe the mosaicity and (ii) to continuously change the balance
between surface and volume effects. In the case of parallel plate cells, commensurability was observed everywhere throughout
the sample, hence ruling out possible effects of mosaicity to explain the q-fold symmetry of the diffraction patterns previously reported when probed with a spatial resolution of mm2 in rotating anode experiments. In the case of wedge cells, the evolution of X-ray patterns with thickness suggested that
commensurate lockin occurs for sufficiently thick samples with a width that is statistical.
Received 18 January 1999 相似文献
6.
Sebastião PJ Simeão Carvalho P Chaves MR Nguyen HT Ribeiro AC 《The European physical journal. E, Soft matter》2006,20(1):55-61
We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal
compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB8Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised
in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with
the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index
of the material. The long-period modulation is temperature dependent and disappears for thin sample cells (< 5μm). The short-period
modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model
which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser
plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure
proposed for this phase. DB8Cl presents a structure formed by dimers that can be viewed as flexible bent-core-like molecules, showing similarities with
phases found in banana-like systems, but exhibiting a much more complex structure. 相似文献
7.
8.
We investigated SmC* films sandwiched between silane coated glass plates and observed formation of textures exhibiting a uniform tilt of the smectic
layers with respect to the boundary plates. The layer tilt angle increases from zero to as the sample is cooled from the smectic A phase to room temperature. These films show linear electro-optical effects because
the permanent polarization can be aligned so that it has a component parallel to the applied field without changing the layer
structure. Our analysis indicates that mainly two effects determine the layer tilt. On the one hand, the surface tension tends
to minimise the layer tilt. On the other hand, the surface energy promotes the director to be normal to the boundary plates.
Received 17 July 1998 相似文献
9.
A dynamic study of onion phases under shear flow: size changes 总被引:5,自引:0,他引:5
P. Panizza A. Colin C. Coulon D. Roux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):65-74
It has been shown that lyotropic lamellar phases under shear flow form structures corresponding to a close packed assembly
of monodisperse multilamellar vesicles (onions). The size, which is fixed by the shear rate, can vary from a few microns to
a tenth of a micron. In this study, we investigate for the first time the transient behaviour of size changes of onions under
shear flow by means of small angle light scattering, direct microscopic observations, and conductivity measurements. We evidence
two regimes: continuous and discontinuous. The nature of which (continuous or discontinuous) depends on the initial and final
shear rate, and can be described by a dynamic phase diagram.
Received: 14 November 1997 / Received in final form: 2 March 1998 / Accepted: 9 March 1998 相似文献
10.
A.C. Ribeiro L. Oswald J.F. Nicoud D. Guillon Y. Galerne 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):503-512
The characterization by optical microscopy, X-ray diffraction and differential scanning calorimetry of two new liquid crystalline
compounds is presented. The compounds under consideration incorporate in their molecules two chiral centres (one asymmetric
carbon and one asymmetric sulphur of a sulphinate group). While the carbon chirality is fixed in the R configuration the sulphur
chirality may be either in the S or in the R configuration. A mesophase in a large temperature domain is evidenced for one of the two diastereomers, while both and mesophases are observed in a similar temperature domain for the other one. For both diastereomers and in both mesophases
it is possible to observe the coexistence of two different types of optical textures, namely planar cholesteric textures and
developable domains. The latter are coiled in a different way than proposed in an earlier publication. More precisely, they
form cylindrical or cone-like domains with double-twist properties as observed in the blue phases. The pitch of the helix
in the TGB mesophases is evaluated by means of optical reflection observations in samples exhibiting the planar cholesteric
textures. For both diastereomers it is also possible to evaluate structural parameters related to the organization within
the mesophases. Finally, the induced phase transition - is studied by the application of an AC electric field.
Received: 16 June 1997 / Revised: 17 October 1997 / Accepted: 20 November 1997 相似文献
11.
Fernandes P Barois P Grelet E Nallet F Goodby JW Hird M Micha JS 《The European physical journal. E, Soft matter》2006,20(1):81-87
We report X-ray resonant scattering experiments performed on the prototype liquid-crystalline compound MHPOBC doped with a
chemical probe containing a resonant atom (selenium). We determined directly for the first time the microscopic 3- and 4-layer
structure of the ferrielectric subphases ( SmCFI1* and SmCFI2*) present in MHPOBC. Despite the low fraction of the selenium probe, the resonant signal is strong enough to allow an unambiguous
determination of the basic structure of the ferrielectric subphases. These experiments demonstrate that the resonant scattering
technique can be extended to liquid crystalline materials without resonant element and may stimulate new studies. A non-resonant Bragg reflection was also found in the SmCFI1* phase in pure MHPOBC, consistent with the 3-layer distorted model, but never detected before. 相似文献
12.
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
13.
Brimicombe PD Roberts NW Jaradat S Southern C Wang ST Huang CC Dimasi E Pindak R Gleeson HF 《The European physical journal. E, Soft matter》2007,23(3):281-287
A binary mixture of an antiferroelectric liquid-crystal material containing a selenium atom and a highly chiral dopant is
investigated using resonant X-ray scattering. This mixture exhibits a remarkably wide four-layer intermediate smectic phase,
the structure of which is investigated over a temperature range of 16K. Analysis of the resonant X-ray scattering data allows
accurate measurement of both the helicoidal pitch and the distortion angle as a function of temperature. The former decreases
rapidly as the SmC
* phase is approached, whilst the latter remains constant over the temperature range studied at 8°±3° . We also observe that the senses of the helicoidal pitch and the unit cell of the repeating four-layer structure are opposite
in this mixture and that there is no pitch inversion over the temperature range studied. 相似文献
14.
R. Kemkemer D. Kling D. Kaufmann H. Gruler 《The European physical journal. E, Soft matter》2000,1(2-3):215-225
In culture migrating and interacting amoeboid cells can form nematoid arrangements in analogy to a nematic liquid crystal
phase. A nematoid arrangement is formed if the interaction has an apolar symmetry. Different cell types like human melanocytes
(= pigment cells of the skin), human fibroblasts (= connective tissue cells), human osteoblasts (= bone cells), human adipocytes
(= fat cells) etc., form a nematoid structure. Our hypothesis is that elastic properties of these nematoid structures can
be described in analogy to that of classical nematic liquid crystals. The orientational elastic energy is derived and the
orientational defects (disclination) of nematoid arrangements are investigated. The existence of half-numbered disclinations
shows that the nematoid structure has an apolar symmetry. The density- and order parameter dependence of the orientational
elastic constants and their absolute values are estimated. From the defect structure, one finds that the splay elastic constant
is smaller than the bend elastic constant (melanocytes). The core of a disclination is either a cell free space or occupied
by non oriented cells (isotropic state), by a cell with a different symmetry, or by another cell type.
Received 3 May 1999 and Received in final form 29 September 1999 相似文献
15.
16.
O. Mondain-Monval J.C. Dedieu T. Gulik-Krzywicki P. Poulin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):167-170
The role of surface energy in the behavior of colloidal particles in liquid crystalline phases is investigated. When the surface
energy dominates, a hedgehog defect is formed and, according to an electrostatic analogy, the distortions around the particles
exhibit a dipolar character. By contrast, for weaker anchoring, the configuration becomes quadrupolar as evidenced by the
structure of latex clusters in lyotropic systems and the observation of defects reminiscent of Saturn rings in thermotropic
systems.
Received 21 June 1999 相似文献
17.
We study the interplay between thermal undulations and electrostatic interactions for weakly charged surfactant bilayers by
measuring the backscattering of light from very dilute lamellar phases of the non-ionic surfactant triethylene glycol monodecyl
ether (C10E3) doped with small amounts of the anionic surfactant sodium dodecyl sulphate (SDS), both with and without added electrolyte.
Upon charging, the lamellar phases show a transition from undulation to electrostatic stabilization. Non-lamellar structures
develop if the molar mixing ratio exceeds . Deviations from ideal swelling, , where is the lamellar repeating distance and the membrane volume fraction, were detected for all lamellar phases. Salt-free lamellar phases with charge densities below
, as well as more highly charged lamellar phases at high ionic strength show a universal logarithmic deviation from ideal
swelling that was analyzed using theories for undulation stabilized lamellar phases. Deviations from ideal swelling for electrostatically
stabilized lamellar phases were analyzed using theories recently developed for undulations in charged lamellar phases. The
fits to the various theories yield a value of for the bending modulus of the C10E3 bilayers.
Received 21 June 1999 and Received in final form 25 August 1999 相似文献
18.
G. Bouglet C. Ligoure 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):137-147
Small angle X-ray and neutron scattering data on an effective three-component lamellar phase composed of water, a non adsorbing
water-soluble polymer (polyvynilpyrolidone), fluid membranes, made from a mixture of a cationic surfactant (cetylpiridiumchloride)
and a cosurfactant (hexanol), are presented for various membrane as well as polymer concentrations. The data are fitted with
a recently proposed model which takes into account the geometry and the fluctuations of these periodic structures. This allows
a quantitative study of the polymer contribution to the smectic compression modulus of the lamellar phase. Four different regimes of polymer confinement are expected. The associated variations in are compared to a recent theoretical model, which predicts the polymer-mediated contribution to the smectic compression modulus.
Received 20 January 1998 相似文献
19.
J.-F. Berret D.C. Roux P. Lindner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):67-77
We have investigated the simple shear flow behavior of wormlike micelles using small-angle neutron scattering and mechanical
measurements. Ternary surfactant solutions made of cetylpyridinium chloride, hexanol and brine (0.2 M NaCl) and hereafter
abbreviated as CPCl-Hex were studied in the concentrated regime, . In a preliminary report (Berret et al. [#!ref16!#]), the discontinuity of slope observed in the shear stress versus shear rate curve was interpreted in terms of first-order phase transition between an isotropic state and a shear-induced
nematic state ( transition). At the transition rate, , the solution exhibits a macroscopic phase separation into viscous and fluid layers (inhomogeneous shear flow). Above a second
characteristic shear rate, the flow becomes homogeneous again, the sheared solution being nematic only. The neutron patterns
obtained in the two-state inhomogeneous region have been re-examined. Based on a consistent analysis of both orientational
and translational degrees of freedom related to the wormlike micelles, we emphasize new features for the transition. In the present paper, the shear rate variations of the relative proportions of each phase in the two-state region,
as well as the viscosity ratio between isotropic and nematic phases are derived. We demonstrate in addition that slightly
above the transition rate, the shear induced nematic phase is already strongly oriented, with an order parameter P
2
= 0.65. The orientational state is that of a nematic flow-oriented monodomain. Finally, from the locations of the neutron
scattering maxima for each isotropic and nematic contributions, we evaluate the concentrations for each phase and and derived a dynamical phase diagram of CPCl-Hex, in terms of the stress
versus
and . According to the classification by Schmitt et al. [#!ref22!#], the transition observed in CPCl-Hex micellar solutions could result from a positive flow-concentration coupling, in agreement
with the observed monotonically increasing shear stress in the two-phase region.
Received: 16 February 1998 / Revised: 18 February 1998 /
Accepted: 24 May 1998 相似文献
20.
B.I. Ostrovskii S.N. Sulyanov N.I. Boiko V.P. Shibaev W.H. de Jeu 《The European physical journal. E, Soft matter》2001,6(4):277-285
The phase behaviour and structure are reported of a new type of frustrated side-chain liquid crystalline (LC) polymer, a polyacrylate
with phenylbenzoate mesogenic side groups and a narrow polydispersity. At a high degree of polymerisation the LC polymers
show a nematic, a smectic-Ad, a re-entrant nematic and a C phase, for shorter chains only a nematic and a C phase. This constitutes a new example of nematic
re-entrance for which the driving field is the length of the polymer chain. The smectic-Ad layers consist of partially overlapped side groups while in the C phase the side chains are rearranged into chevron-like
blocks of bilayers. We propose an explanation of the frustrated phase behaviour in terms of these two different competing
length scales and their coupling to the backbone conformations.
Received 28 February 2001 and Received in final form 6 August 2001 相似文献