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1.
In this paper, we discuss the equilibrium phases and collapse transitions of a lyotropic nematic gel immersed in an isotropic
solvent. A nematic gel consists of a cross-linked polymer network with rod-like molecules embedded in it. Upon decreasing
the quality of the solvent, we find that a lyotropic nematic gel undergoes a discontinuous volume change accompanied by an
isotropic-nematic transition. We also present phase diagrams that these systems may exhibit. In particular, we show that coexistence
of two isotropic phases, of two nematic phases, or of an isotropic and a nematic phase can occur.
Received 15 February 2002 and Received in final form 14 June 2002 相似文献
2.
3.
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
4.
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
5.
Spontaneous thermal expansion of nematic elastomers 总被引:1,自引:0,他引:1
We study the monodomain (single-crystal) nematic elastomer materials, all side-chain siloxane polymers with the same mesogenic
groups and crosslinking density, but differing in the type of crosslinking. Increasing the proportion of long di-functional
segments of main-chain nematic polymer, acting as network crosslinking, results in dramatic changes in the uniaxial equilibrium
thermal expansion on cooling from the isotropic phase. At higher concentration of main chains their behaviour dominates the
elastomer properties. At low concentration of main-chain material, we detect two distinct transitions at different temperatures,
one attributed to the main-chain, the other to the side-chain component. The effective uniaxial anisotropy of nematic rubber,
r(T) = / proportional to the effective nematic order parameter Q(T), is given by an average of the two components and thus reflects the two-transition nature of thermal expansion. The experimental
data is compared with the theoretical model of ideal nematic elastomers; applications in high-amplitude thermal actuators
are discussed in the end.
Received 25 June 2001 and Received in final form 29 September 2001 相似文献
6.
W.D. Heiss H.L. Harney 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):149-151
Exceptional points are singularities of the spectrum and wave functions of a Hamiltonian which occur as functions of a complex
interaction parameter. They are accessible in experiments with dissipative systems. We show that the wave function at an exceptional
point is a specific superposition of two configurations. The phase relation between the configurations is equivalent to a
chirality which should be detectable in an experiment.
Received 9 April 2001 and Received in final form 19 July 2001 相似文献
7.
We theoretically model the nucleation of nematic droplets during phase ordering in mixtures of a flexible polymer and a low-molecular-weight
liquid crystal. By appealing to classical nucleation theory (CNT), we calculate the energy barrier to nucleation and the size
of a critical nucleus. We study the influence of a metastable intermediate phase on the nucleation of the nematic. Below a
triple point in the phase diagram, there are two distinct mechanisms for the formation of a nematic nucleus: 1) direct nucleation
from the isotropic phase and 2) nucleation via a precursor metastable isotropic phase. We calculate the crossover concentration as a function of temperature, delineating
the regions of the phase diagram in which each mechanism prevails. In the latter case, the presence of a hidden metastable
isotropic-isotropic binodal may either promote or delay the nucleation of a nematic phase.
Received 9 August 2002
RID="a"
ID="a"e-mail: matuyama@chem.mie-u.ac.jp 相似文献
8.
Bernazzani P Simon SL Plazek DJ Ngai KL 《The European physical journal. E, Soft matter》2002,8(2):201-207
The process of spin-coating to fabricate thin polymer films with high molecular weight can produce samples with entanglement
concentrations that are far below the equilibrium value. It is not clear whether or not such low entanglement concentrations
are responsible for the depression of the glass temperature in thin polymer films. In this work, we measure the calorimetric
glass temperature and viscoelastic response of polystyrenes with molecular weights ranging from 3×103 to 43.7×106 g/mol, for both bulk material and for samples freeze-dried from dilute solution. We conclude that the reduction of the glass
temperature observed in thin polymer films cannot be due to the reduced entanglement concentration in the samples.
Received 15 August 2001 and Received in final form 2 March 2002 相似文献
9.
The interaction between two parallel plates due to non-adsorbing polymer chains with excluded volume is calculated using the
adsorption method. The adsorption is calculated from the profile of the polymer segment concentration between the plates,
which is obtained from the product function of the concentration profile near a single wall, involving the correlation length.
The renormalization group theory provides expressions for the osmotic pressure and consequently for the osmotic compressibility,
chemical potential and correlation length of a polymer solution. Both the local polymer concentration profiles as well as
the minimum of the interaction potential between the plates agree with recently published self-avoiding random walk computer
simulations.
Received 9 August 2001 相似文献
10.
G.G. Pereira 《The European physical journal. E, Soft matter》2002,7(3):273-289
The inherent nanoscale morphologies of self-organizing diblock copolymer melts are now being investigated for a variety of
technological applications. To obtain global, well-oriented, regular patterns requires suitably confining and aligning the
melt between two flat plates. Here we consider such confinement for an asymmetrical diblock melt, which forms columns of the
minority phase in a matrix of the majority phase. We investigate this system with a combination of numerical simulations and
strong segregation theory and make suggestions as to when perpendicular orientation should prevail over parallel orientation
of the columns.
Received 22 May 2001 and Received in final form 14 February 2002 相似文献
11.
L. Spindler I. Drevenšek Olenik M. Čopič R. Romih J. Cerar J. Škerjanc P. Mariani 《The European physical journal. E, Soft matter》2002,7(1):95-102
Self-assembling properties of deoxyguanosine 5'-monophosphate in isotropic solutions of concentrations from 0.5 wt% to 15
wt% were investigated by dynamic light scattering (DLS) and 31P NMR spectroscopy. A slow diffusive mode with a diffusion coefficient D
slow∼ 10-12 m2/s was detected by DLS for the whole concentration range. This mode is assigned to the translational motion of large globular
aggregates, similar to those observed in DNA and other polyelectrolyte solutions. The existence of such aggregates was confirmed
by freeze fracture electron microscopy. Close to the isotropic-cholesteric phase transition, at 4 wt%
c
10 wt%, also a faster diffusive mode is observed in the polarized DLS response and a very fast mode is detected by depolarized
DLS. These modes are related to translational and rotational diffusion of the columnar stacks of guanosine molecules, which
are favorably formed in the relatively narrow pretransitional region. The stacking was also revealed from the appearance of
a secondary resonance line in the 31P NMR spectra. Using the hydrodynamic theory of Tirado and Garcia de la Torre, the length of the cylindrical stacks was found
to be L = 364±78 ?, which is significantly larger than the values reported for other guanosine derivatives.
Received 13 July 2001 and Received in final form 17 October 2001 相似文献
12.
V. Pot T. Karapiperis 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):387-393
We developed a numerical model based on a multi-species lattice gas cellular automaton to study passive and reactive tracer
migration in saturated geological media. The model was made of multiple lattice gases interacting via a two-species collision rule. For a binary mixture, the model displayed a negative deviation from Raoult's law and therefore
behaved as a real solution. By biasing the initial two-species collision rule, our model was made to obey the tracer assumption
which requires that the tracer species does not affect the velocity of the vehicle fluid. In a 2D fracture, we checked the
Taylor-Aris relation. An irreversible adsorption between the tracer and the solid phase was numerically added to perform filtration
of the colloids. A good agreement was found with the solution of the filtration equation. An attachment efficiency was defined
and was found to bear a linear relationship to the filtration coefficient. We added a third species to study the potential
role of colloids in the transport of contaminants. Contaminant migration was enhanced when contaminants were bound to colloids
and was slightly reduced when colloids were allowed to adsorb on the solid phase.
Received 14 January 1999 and Received in final form 8 June 1999 相似文献
13.
Adhikari R 《The European physical journal. E, Soft matter》2002,9(2):127-134
We calculate the elastic-field-mediated interaction between macroscopic particles in a columnar hexagonal phase. The interaction
is found to be long-ranged and non-central, with both attractive and repulsive parts. We show how the interaction modifies
the particle correlations and the column fluctuations. We also calculate the interaction of particles with the topological
defects of the columnar phase. The particle-defect interaction reduces the mobility of the defects.
Received 14 March 2002 and Received in final form 13 August 2002
RID="a"
ID="a"e-mail: rjoy@physics.iisc.ernet.in 相似文献
14.
B.I. Ostrovskii D. Sentenac I.I. Samoilenko W.H. de Jeu 《The European physical journal. E, Soft matter》2001,6(4):287-294
We report on the thin-film behaviour of a polyacrylate with phenyl benzoate mesogenic side groups and a narrow polydispersity.
Depending on the degree of polymerisation, these polymers show a nematic, a smectic-A d, a re-entrant nematic and a C phase with a two-dimensional monoclinic lattice. X-ray reflectivity and atomic-force microscopy
have been used to characterize the structure and surface morphology. The system exhibits two stable side-chain packing configurations
with incommensurate spacings that can be both stabilized at a free surface. Thin films in the nematic phase show a structural
dewetting induced by the growth of surface domains of the C phase. Additionally, surface-induced ripples with a nanoscale
lateral period form at the air-film interface. We attribute these patterns to a coupling between the local liquid crystalline
ordering of the mesogenic side groups and the surface curvature energy.
Received 28 February 2001 and Received in final form 6 August 2001 相似文献
15.
M. Auslender E. Kogan 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):525-529
We study density of states and conductivity of the doped double-exchange system, treating interaction of charge carriers both
with the localized spins and with the impurities in the coherent potential approximation. It is shown that under appropriate
conditions there is a gap between the conduction band and the impurity band in paramagnetic phase, while the density of states
is gapless in ferromagnetic phase. This can explain metal-insulator transition frequently observed in manganites and magnetic
semiconductors. Activated conductivity in the insulator phase is numerically calculated.
Received 13 June 2000 and Received in final form 5 January 2001 相似文献
16.
The static structure factor (S(q)) of dispersions and gels of disk-like mineral colloids (Laponite) was investigated using time- and ensemble-averaged light
scattering. The evolution of S(q) in time after increasing the ionic strength of well-dispersed Laponite suspensions shows that Laponite aggregates and forms
fractal clusters. The structure of the aggregates does not depend on the ionic strength, but the rate of growth increases
very strongly with the ionic strength. At concentrations below about 3 g/l (0.12% v/v) the aggregates sediment while at higher
concentrations space-filling gels are formed. The gels are homogeneous on length scales larger than the correlation length
which decreases strongly with decreasing ionic strength and increasing concentration. However, the local structure is the
same, independent of the concentration and the ionic strength.
Received 6 August 2000 and Received in final form 16 March 2001 相似文献
17.
We discuss the coupling between flow and other hydrodynamic variables that can occur in the optically isotropic tetrahedratic
phase (Td) characterized by a third rank tensor order parameter Tijk. We point out that an applied electric field or an applied temperature gradient will lead to flow. Reciprocally we predict
that, for example, a shear flow applied to a tetrahedratic phase leads to an induced electric field and a temperature gradient.
Similarities to recent experimental observations in the vicinity of the isotropic-B7 phase transitions in materials formed
by banana-shaped molecules are discussed.
Received 31 July 2001 相似文献
18.
T. Vuletić P. Auban-Senzier C. Pasquier S. Tomić D. Jérome M. Héritier K. Bechgaard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):319-331
The phase diagram of the organic superconductor (TMTSF)2PF6has been revisited using transport measurements with an improved control of the applied pressure. We have found a 0.8 kbar
wide pressure domain below the critical point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground state
featuring a coexistence regime between spin density wave (SDW) and superconductivity (SC). The inhomogeneous character of
the said pressure domain is supported by the analysis of the resistivity between T
SDW
and T
SC
and the superconducting critical current. The onset temperature T
SC
is practically constant ( 1.20±0.01 K) in this region where only the SC/SDW domain proportion below T
SC
is increasing under pressure. An homogeneous superconducting state is recovered above the critical pressure with T
SC
falling at increasing pressure. We propose a model comparing the free energy of a phase exhibiting a segregation between
SDW and SC domains and the free energy of homogeneous phases which explains fairly well our experimental findings.
Received 3 September 2001 and Received in final form 9 November 2001 相似文献
19.
Equilibrium structures of planar polyelectrolyte brushes formed by grafted chains carrying charges of opposite sign are examined
by employing mean-field lattice theory. Two brushes of different architecture are considered: one formed by grafted diblock
copolymers with oppositely charged blocks and the other being a mixed brush composed of oppositely charged homopolymers. The
systems display nontrivial intrinsically inhomogeneous brush structures originating from the chain connectivity and the electrostatic
interaction among the segments. In addition, a coexistence of stretched and coiled chains inside the brush is observed. The
influence of the charges of the blocks, the relative length of the oppositely charged blocks, and the ionic strength of the
solution on the brush inhomogeneity and structural differences between the two types of brushes are discussed.
Received 14 March 2001 and Received in final form 18 June 2001 相似文献
20.
Vivarès D Belloni L Tardieu A Bonneté F 《The European physical journal. E, Soft matter》2002,9(1):15-25
We present the experimental and theoretical background of a method to characterize the protein-protein attractive potential
induced by one of the mostly used crystallizing agents in the protein-field, the poly(ethylene glycol) (PEG). This attractive
interaction is commonly called, in colloid physics, the depletion interaction. Small-Angle X-ray Scattering experiments and
numerical treatments based on liquid-state theories were performed on urate oxidase-PEG mixtures with two different PEGs (3350
Da and 8000 Da). A “two-component” approach was used in which the polymer-polymer, the protein-polymer and the protein-protein
pair potentials were determined. The resulting effective protein-protein potential was characterized. This potential is the
sum of the free-polymer protein-protein potential and of the PEG-induced depletion potential. The depletion potential was
found to be hardly dependent upon the protein concentration but strongly function of the polymer size and concentration. Our
results were also compared with two models, which give an analytic expression for the depletion potential.
Received 29 April 2002
RID="a"
ID="a"Present address: CRMC2-CNRS, Campus de Luminy, case 913, F-13288 Marseille Cedex 09, France; e-mail: vivares@crmc2.univ-mrs.fr
RID="b"
ID="b"e-mail: bonnete@crmc2.univ-mrs.fr
RID="c"
ID="c"Laboratory associated to Universities Aix-Marseille II and III. 相似文献