共查询到20条相似文献,搜索用时 46 毫秒
1.
I. Sabbagh M. Delsanti P. Lesieur 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):253-260
Anomalous small angle X-ray scattering experiments show that before demixion in sodium polyacrylate/cobalt and sodium polyacrylate/calcium
mixtures all the divalent counterions are in the close vicinity of the polyacrylate chain. The present results are consistent
with previous UV/VIS spectroscopy, which have shown that all cobalt ions are chemically associated with acrylate groups. The
chemical association dehydrates the acrylate monomers. However, the hydrophobicity of the complexed monomers is not strong
enough to induce a collapse of the polymer chain at small spatial scale before the demixion. Indeed, the scattered intensity
(X-ray and neutron scattering) decreases with the scattering vector q as q-x with for q > 0.1 nm
-1 which indicates that the local conformation of the chain is Gaussian.
Received 21 January 1999 相似文献
2.
J.J. Arenzon J.F. Stilck Y. Levin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):79-82
We present a simple model for the possible mechanism of appearance of attraction between like charged polyions inside a polyelectrolyte
solution. The attraction is found to be short ranged, and exists only in the presence of multivalent counterions. It is produced
by the correlations in layers of condensed counterions surrounding each polyion and is only weakly temperature dependent.
We find the attraction to be maximum at zero temperature and dimish as the temperature is raised. The attraction is only possible
if the number of condensed counterions exceeds the threshold, , where is the valence of counterions and Z is the polyion charge.
Received 10 March 1999 and Received in final form 20 April 1999 相似文献
3.
Single- and double-stranded DNA and many biological and synthetic polyelectrolytes undergo two structural transitions upon
increasing the concentration of multivalent salt or molecules. First, the expanded-stretched chains in low monovalent salt
solutions collapse into nearly neutral compact structures when the density of multivalent salt approaches that of the monomers.
With further addition of multivalent salt the chains redissolve acquiring expanded-coiled conformations. We study the redissolution
transition using a two-state model (F.J. Solis, M. Olvera de la Cruz, J. Chem. Phys. 112, 2030 (2000)). The redissolution occurs when there is a high degree of screening of the electrostatic interactions between
monomers, thus reducing the energy of the expanded state. The transition is determined by the chemical potential of the multivalent
ions in the solution, μ and the inverse screening length, κ. The transition point also depends on the charge distribution
along the chain but is nearly independent of the molecular weight and degree of flexibility of the polyelectrolytes. We generate
a diagram of μversusκ2 where we find two regions of expanded conformations, one with charged chains and the other with overcharged (inverted charge)
chains, separated by a collapsed nearly neutral conformation region. The collapse and redissolution transitions occur when
the trajectory of the properties of the salt crosses the boundaries between these regions. We find that in most cases the
redissolution occurs within the same expanded branch from which the chain precipitates.
Received 15 May 2000 and Received in final form 28 June 2000 相似文献
4.
V.A. Pryamitsyn A.N. Semenov T.C.B. McLeish 《The European physical journal. E, Soft matter》2001,4(2):161-171
An analytical one-dimensional model of the microphase separation in symmetric diblock copolymers is developed. Three stages
of the process of the microphase segregation of a quenched diblock copolymer system into a lamella structure are predicted.
The first stage involves a fast increase of the amplitude of the quasi-periodical lamella structure (with the average wave
vector q0) up to a nearly equilibrium value; the second stage is a slow phase diffusion process which is characterized by increasing
coherency of the lamella structure; the third stage is the slow process of the lamella swelling, which is driven by the thermally
activated process of the spontaneous deletion of excessive lamellas, the lamella size increasing from the initial value 2π/q
0 to the equilibrium 2π/q
eq > 2π/q
0 during the process. The last two stages are described with the specially introduced coarse-grained “amplitude-phase” approximation.
It is shown that the relaxation of the gradient of the phase of the lamellar structure is the slowest relaxation process and,
thus, can be used as an effective order parameter of the lamellar structure at the later stages of the microphase segregation.
Received 10 March 2000 and Received in final form 5 June 2000 相似文献
5.
K. Singh S.M. Pande S.W. Anwane S.S. Bhoga 《Applied Physics A: Materials Science & Processing》1998,66(2):205-215
2 SO4. The solid solubility limits up to x≤3 mole% for monovalent, x≤5.27 mole% for divalent and x≤3.63 mole% for trivalent cation
doped Ag2SO4 are set with XRD, SEM, IR and DSC techniques. A predominant dependence of conductivity on the ionic size of iso- and alio-valent
cations is observed. In particular, the conductivity enhances in both α and β phases, despite having a lower ionic-size dopant
cation (relative to that of Ag+) in the transition element cation doped Ag2SO4. Ca2+, Ba2+, Y3+ and Dy3+ doped samples show depature from the regular behaviour in the β-phase. The conductivity behaviour is discussed considering
ionic size, valence and electronic structure of the guest cations.
Received: 3 February 1997/Accepted: 27 May 1997 相似文献
6.
Chemical-bond analysis of the nonlinear optical properties of the borate crystals LiB3O5, CsLiB6O10, and CsB3O5 总被引:1,自引:0,他引:1
The second-order nonlinear optical properties of practical borate crystals, LiB3O5, CsLiB6O10, and CsB3O5, which all contain the identical basic structural unit [the (B3O7)5- group], have been quantitatively studied from the chemical-bond viewpoint. Differences in the nonlinear optical properties
among these three borate crystals arise from the contributions of the different cations, i.e., the different interaction between
the cation and the (B3O7)5- anionic group. The chemical-bond method quantitatively expresses this important difference. At the same time, the current
calculation also shows that the B3O7 group is a very important crystallographic frame in the crystalline borate solids; it offers different cations an excellent
coordination environment.
Received: 20 February 2001 / Accepted: 14 June 2001 / Published online: 30 August 2001 相似文献
7.
Spherical polyelectrolyte block copolymer micelles: Structural change in presence of monovalent salt
Muller F Guenoun P Delsanti M Demé B Auvray L Yang J Mays JW 《The European physical journal. E, Soft matter》2004,15(4):465-472
Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSSd)251 and a short hydrophobic moiety (PEP)52. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, Rs, remains essentially constant and a contraction is observed above an added-salt concentration cs of 2×10-2 M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: Rs cs-0.18. The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length. 相似文献
8.
2 O3, AlN and Si substrates produced by vacuum ultraviolet induced decomposition of palladium acetate is described. The palladium
films formed and the palladium acetate layers used were characterised by using ultraviolet spectrophotometry and Fourier transform
infrared (FTIR) spectroscopy. The optical transmission of the films after irradiation with pseudo-continuous 126 nm radiation
generated by an excimer lamp provided information about the decomposition rate at different pressures and exposure times.
The FTIR spectra recorded the chemical changes of the C=O, COO- and CH3 groups at different exposure times. The decomposition mechanism of the palladium acetate under these conditions appears to
be quite different to that induced by pulsed laser irradiation.
Received: 25 November 1996/Accepted: 1 July 1997 相似文献
9.
The self-diffusion coefficient of 22Na+ and the ionic conductivity are measured as a function of temperature in NaCl single crystals doped with labelled yttrium ions, as well as the diffusion coefficient of 88Y3+. We give the theoretical equations for the transport processes in the alkali halides doped with a trivalent cation; These are derived from the theory of the crystals doped with divalent cations. Solubility of YCl3 in NaCl is accurately determined through a radioactive technique. The free enthalpy of solubility of free Y3+ is: (2.91?13 kT) eV. A good fit of the whole set of data is obtained by treating the association between Y3+ ions and vacancies by the single equation . The jump frequency of Y3+ is . The results are compared to those characterising the divalent foreign cations. 相似文献
10.
D. Beckmann S. Wanka J. Wosnitza G. Goll B. Drehmann E. Balthes D. Schweitzer W. Strunz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):329-333
We report on Shubnikov-de Haas and de Haas-van Alphen measurements of an organic metal based on the molecular donor bis(ethylenedioxy)-tetrathiavulvalene
(= BEDO-TTF) and the anion Cl- with H2O molecules. The observed single oscillation frequency perfectly follows the two-dimensional dependence with T. The Fermi-surface area of of the first Brillouin zone proves a quarter-filled band, i.e., a 2:1 stoichiometry of the BEDO-TTF donor with respect to the anion. The apparent discrepancy to X-ray data which give a
1:1 ratio between BEDO-TTF and Cl- is understood by replacement of H2O molecules with (H3O)+ ions. The proposed stoichiometry therefore is (BEDO-TTF)2
+(H5O2)+(Cl-)2. The cyclotron effective mass is when deduced from the temperature dependence of the fundamental oscillation amplitude, but strongly reduced when extracted
from higher harmonics. This and the strong harmonic content of the oscillations signals an influence of the two-dimensional
electronic structure and can be qualitatively understood by applying the concept of magnetic interaction to the effect of
the oscillatory chemical potential.
Received: 16 April 1998 / Revised: 7 July 1998 / Accepted: 9 July 1998 相似文献
11.
Oelschlaeger C Buhler E Waton G Candau SJ 《The European physical journal. E, Soft matter》2003,11(1):7-20
The mixed micellization between the cationic gemini surfactant [ C12H25( CH3)2N+( C2H4) N+( CH3)2 C12H25•2Br-] and the cationic cetyltrimethylammonium bromide (CTAB) in 150 mM KBr solutions has been investigated. The variation of the
cmc of the mixtures, measured by surface tension experiments, with composition revealed synergism in micelle formation. T-Jump
and light scattering experiments performed in the vicinity of the crossover volume fraction showed the existence of two micellar
populations, possibly linear and toroidal micelles. Rheological and dynamic light scattering experiments allowed to fully
characterize the linear viscoelasticity of the mixtures. These measurements revealed synergistic gains in viscoelastic properties
with a maximum of the stress-relaxation time around the equimolar composition. These effects are ascribed to a progressive
intermicellar crosslinking resulting from a continuous increase of the end-cap energy with the 12-2-12 content in the mixture.
Received: 18 November 2002 / Accepted: 8 April 2003 / Published online: 27 May 2003
RID="a"
ID="a"e-mail: candau@fresnel.u-strasbg.fr 相似文献
12.
本文利用红外光解离光谱研究了第三族金属氧化物离子对二氧化碳分子的转化机制. 研究表明,对于[ScO(CO2)n]+体系,在n≤4时,形成了溶剂化结构;在n=5时,形成了碳酸盐结构,实现了二氧化碳的转化. 对于[YO(CO2)n]+体系,需要4个二氧化碳分子就可以实现二氧化碳的转化. 而在[YO(CO2)n]+体系中,只发现了溶剂化结构,没有观察到碳酸盐结构. 理论计算表明,[YO(CO2)n]+体系拥有最小的溶剂化结构向碳酸盐结构转化能垒,[LaO(CO2)n]+体系拥有最大的溶剂化结构向碳酸盐结构转化能垒. 本文从分子水平揭示了不同金属氧化物离子对二氧化碳分子转化的影响规律. 相似文献
13.
M. Mukoujima K. Kawabata T. Sambongi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):365-369
Intermittent and irregular motion of isolated twin boundary (kink) in organic crystal (TMTSF)2PF6 was studied at room temperature. Both the local velocity and the time of intermission are determined not only by external
stress and temperature but also by the time (t
w) elapsed after the backward passage and before the following forward one. When the kink moves after longer t
w, its velocity becomes smaller and the time of intermission longer. Both tend to saturate for t
w longer than 102 s. This result indicates that some disorder is induced in the lattice by the backward motion and it is relaxed during t
w. We also found that the effect of the backward motion of one kink on its following motion is equivalent quantitatively to
that of the forward motion of the pair-created counterpart.
Received: 14 April 1998 / Received in final form and Accepted: 1st September 1998 相似文献
14.
A. Albersdörfer E. Sackmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):663-672
In this paper we study the effect of monovalent and divalent ions on the swelling behavior and viscoelastic parameters of ultrathin layers of the natural polyelectrolyte hyaluronic acid
covalently coupled to glass substrates. A colloidal probe technique is applied for this purpose based on latex beads, hovering over the polymer cushion. By analyzing the vertical Brownian motion of these beads with reflection
interference contrast microscopy (RICM) we determined the equilibrium layer thickness (with 3 nm vertical resolution), the
interfacial interaction potential, and the characteristic mesh size limiting the hydrodynamic flow within the polyelectrolyte
film as a function of the ionic strength. The experimental results are interpreted in terms of three different theoretical
models: the polyelectrolyte brush approximation of Pincus [#!ref1!#], a modified polyelectrolyte brush approximation in the
high salt concentration limit of Ross and Pincus [#!ref2!#] and the simple scaling approximation for neutral adsorbed polymers
of de Gennes [#!ref3!#]. Within experimental error all of these different models fit our experimental data and yield comparable
results for the equilibrium layer thickness. Moreover we determine a thickness dependent, effective surface coverage from
both brush models. The hydrodynamic properties of the films are interpreted in terms of the Brinkmann model of elastic porous
media by assuming an effective mesh size, which depends linearly on the Debye screening length. The salt induced condensation
of the polyelectrolyte films can be described microscopically in terms of a progressive contraction of the mesh size with
increasing salt concentration.
Received 10 September 1998 and Received in final form 30 November 1998 相似文献
15.
M. G. Brik 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):269-274
Systematic first-principles analysis of the energy level schemes and ground
state absorption spectra of trivalent chromium in ZnAl2S4 and
ZnGa2O4 crystals has been performed in the present paper. The
recently developed first-principles approach to the analysis of the
absorption spectra of impurity ions in crystals based on the discrete
variational multi-electron (DV-ME) method [K. Ogasawara et al., Phys. Rev. B
64, 115413 (2001)] was used in the calculations. The method is based on the
numerical solution of the Dirac equation; no phenomenological parameters are
used in the calculations. As a result, complete energy level schemes of the
Cr3+ ion and its absorption spectra in both crystals were calculated,
assigned and compared with experimental data. By performing analysis of the
molecular orbital (MO) population, it was shown that the covalency of the
chemical bonds between the Cr3+ and S2- ions is more significant
than that one between the Cr3+ and O2- ions. 相似文献
16.
The effects of A-site cation size disorder in ABO3 type charge-ordered and antiferromagnetic Pr0.5Ca0.5MnO3 system have been studied by substituting La3+, Sr2+ or Ba2+, while keeping the valency of Mn ions and the tolerance factor (t=0.921) constant in the substituted compounds. We find that the substitutions by these larger cations induce successive sharp step-like metamagnetic transitions at 2.5 K. The critical field for metamagnetism is the lowest for 3% Ba substituted compound, which has the largest A-site cation size disorder and the least distorted MnO6 octahedra, among the compounds reported here. These cation substitutions give rise to ferromagnetic clusters within antiferromagnetic matrix, indicating phase-separation at low temperatures. The growth of the clusters is found to vary with the substitution amount. The local lattice distortion of MnO6 octahedra enhances the charge ordering temperature and reduces the magnetization at high fields (>1 T) in these manganites. 相似文献
17.
3 O5 (LBO) crystal has been studied by using the bond valence theory of complex crystals. Chemical bond parameters and linear
and nonlinear optical (NLO) properties of each type of constituent chemical bonds are quantitatively determined. Because of
the different crystal structure characteristics of LBO from those of β-BaB2O4 (BBO), the two anionic groups, (B3O7)5- in LBO and (B3O6)3- in BBO, play different roles in contributions to their own total NLO tensor coefficients of LBO and BBO, respectively. By
comparison, we find that planar (B3O6)3- groups are the ideal structure model, leading to little cancellation of contributions of each kind of bond in these groups,
and this gives us a useful guide to design new NLO materials in the future.
Received: 24 January 1997/Accepted: 27 March 1997 相似文献
18.
H. Tributsch 《Applied Physics A: Materials Science & Processing》2001,73(3):305-316
Based on the experimental observations that the three-phase nano-TiO2/F:SnO2/I-/I-
3 electrolyte front contact has to have pronounced rectifying properties (reverse reaction with electrolyte suppressed) for
efficient operation of the dye-sensitization solar cell and plays an active part in the generation of photoelectrochemical
energy, an analytical formula is derived which allows the understanding of the relevance and involvement of a variety of kinetic
and cell parameters. Essentially, the TiO2 layer is treated as a photocathode, donating electrons to a kinetically controlled front contact, with the counter-charges
being transported by the electrolyte within the pores. The formula was expanded to include photochemical kinetics of the sensitizer,
for which photodegradation properties were also calculated. The branching ratio, the ratio of regeneration-rate constant of
the sensitizer and of product-formation rate, turned out to be critical for long-term stability. It may have to be improved
by one order of magnitude for efficient cells to reach a lifetime of 20 years.
The degree of rectifying character of the nano-TiO2/F:SnO2/I-/I-
3 electrolyte interface (electric-field-dependent charge transfer to the front contact versus recombination-rate constant with
I3
- distinguishes between a low-efficiency (‘dynamic’) Galvani-type solar cell (efficiency determined by photoinduced chemical
potential gradients, no rectifying contact) and a more highly efficient ‘junction-type’ solar cell (separation and collection
of charges additionally assisted by junction potential). Several controversial subjects are addressed. The key challenges
for the improvement of such cells are discussed, especially with respect to photodegradation and to solid-state devices.
Received: 18 September 2000 / Accepted: 17 January 2001 / Published online: 20 June 2001 相似文献
19.
用XPS研究了标称四价铈盐系列:硫酸铈铵、硫酸铈、二苯基羟乙酸铈、碘酸铈、过氧化铈、二氧化铈以及三价铈盐系列:草酸亚铈、硫酸亚铈、二苯基羟乙酸亚铈、碘酸亚铈和氯化亚铈.结果表明,上述标称四价铈盐都属于混合价化合物,其Ce3d电子能谱呈现Ce4+和Ce3+的二组谱线结构的混合.在真空中加热后CeO2的Ols电子能谱有两个氧峰,这说明 Ce(4f0)O(2pπ)←→Ce(4f1)O(2pn-1) 类型价态波动的可能性较大.三价铈盐的3d谱线的低结合能端约3.5—4eV处则存在摔落伴峰. 相似文献
20.
S. Hébert A. Maignan V. Hardy C. Martin M. Hervieu B. Raveau R. Mahendiran P. Schiffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):419-424
The low temperature magnetic and transport properties of the Pr0.5Ca0.5Mn1-xNixO3 manganites ( 0≤
x
≤0.1) have been investigated. The presence of Ni hinders the charge and orbital ordering observed in Pr0.5Ca0.5MnO3 and favors the creation of ferromagnetic regions, leading to phase separation. The ferromagnetic fractions induced by the
Ni substitution have been estimated from magnetization measurements, they are large and reach 40% for 4% of Ni. Steps are
observed in the M
(
H
) and ρ(
H
) curves of all the samples at T
< 5 K. They are similar to the steps observed in Pr0.5Ca0.5Mn1-xMxO3, where M is a non magnetic cation (Mg2+, Ga3+,...), and for which the ferromagnetic fractions are very small (less than 2%), however, their appearance is restricted to
lower temperatures (T
< 5 K) with Ni dopant than with non magnetic cations. This study shows that steps can be observed in a wide range of phase-separated
systems, even when the ferromagnetic fraction is very large.
Received 5 April 2002 / Received in final form 8 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: antoine.maignan@ismra.fr 相似文献