共查询到20条相似文献,搜索用时 15 毫秒
1.
Monolayers of polystyrene-polyethylene oxide (PS-PEO) copolymers at the air-water interface have been studied with the Modulation
Polarization Infra Red Spectroscopy technique (PM-IRRAS) to measure the orientation of the PEO chains with respect to the
normal to the interface. At surface densities intermediate between the dilute regime and the brush regime, the average tilt
angle has been determined: it decreases continuously with the surface density in the monolayer, in good agreement with previous
results (M.C. Fauréet al., Macromolecules 32, 8538 (1999)). The further stretching of the molecules in the brush regime has also been measured. No substantial volume
fraction of PEO crystal domains has been detected in the very dense regime
Received 16 April 1999 and Received in final form 26 August 1999 相似文献
2.
A. Drzewiński A. Ciach A. Maciolek 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):825-833
The two-dimensional Ising films with bulk H and surface H1 fields of opposite sign are studied above and close to bulk criticality by the density matrix renormalization group method.
This technique, applied recently to d=2 Ising films, allows for very accurate results for the adsorption as a function of the reduced deviation from the critical temperature .For strong H1 three distinct classes of shapes of ,determined by the value of the parameter ,where L is the width of the film, are found in agreement with earlier predictions [A. Macioek, A. Ciach, R. Evans, J. Chem. Phys. 108, 9765 (1998)]. For strong and for weak bulk fields is a monotonic function, increasing for strong H and decreasing for weak H, in agreement with scaling analysis and earlier mean-field results. For H between these extreme cases assumes a maximum for and for a depletion occurs, as in recent experiments for critical adsorption in porous materials. For a limited range of H a qualitatively new behavior of is found. In addition to a maximum, a minimum of for appears, which in the mean-field analysis was absent.
Received: 11 February 1998 / Received in final form: 16 February 1998 / Accepted: 17 March 1998 相似文献
3.
Costa AC Composto RJ Vlcek P Geoghegan M 《The European physical journal. E, Soft matter》2005,18(2):159-166
Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function
of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiOx, and SiOx functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles
for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and
find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy
between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiOx. 相似文献
4.
ALINE F. MILLER MARK R. WILSON MELANIE J. COOK RANDAL W. RICHARDS 《Molecular physics》2013,111(8):1131-1138
Monte Carlo simulations have been carried out for an off-lattice model of an amphiphilic polymer at a hydrophobic/hydrophilic interface. The model system consists of a polynorbornene backbone with poly(ethylene oxide) (PEO) grafts modelled atomistically at an idealized interface between hydrophobic and hydrophilic regions, which are represented by external potentials. Results are presented for the distribution of PEO chain ends, and the density of PEO segments perpendicular to the surface. The latter is used to provide predictions for neutron reflectivity profiles normal to the surface as a function of the lateral confinement of the PEO grafts. At low surface coverage the simulation results are found to be in good agreement with experimental neutron scattering results from similar polymers studied at the water/air interface. 相似文献
5.
P.I.C. Teixeira E.M. Terentjev 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):237-245
We propose a microscopic model of a chiral polymer chain with permanent transverse dipoles interacting with an external electric
field. Its behaviour has been investigated by computer simulation in the limit of weak chirality. Large-scale (tertiary) helical
winding induced along the field direction has been found above a threshold field Ec, and the helix parameters have been calculated as functions of the field strength. Below Ec there is no coherent helical structure of the chain conformation. We find a characteristic scaling of the threshold and the
winding radius a with the chain bending modulus , and .
Received: 15 November 1997 / Accepted: 16 February 1998 相似文献
6.
G. Mattei F. Toigo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):245-256
The effect of non-local norm-conserving pseudo-potentials on the static and dynamic properties of Nan and Lin cluster with n=6,8 is investigated in the frame of self-consistent LDA calculations with spherically averaged ionic density (SAPS model).
A comparison with previous calculations which use local pseudo-potentials as well with uniform averaged non-local pseudo-jellium
calculation has been carried out. A better quantitative agreement with experiments has been found in the calculation of the
photoresponse cross-section with respect to either simple jellium or pseudo-jellium model, even in very small clusters, where
deviations from sphericity are not negligible.
Received: 3 March 1998 / Received in final form and Accepted: 2 June 1998 相似文献
7.
8.
Non-Contact to Contact Transition: Direct Measurements of Interaction Forces between a Solid Probe and a Planar Air-Water Interface
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The interaction force between a solid probe and a planar air-water interface is measured by using an atomic force microscope. It is demonstrated that during the approach of the probe to the air-water interface, the force curves decline all the time due to the van der Waals attraction and induces a stable profile of water surface raised. When the tip approaches very close to the water surface, force curves jump suddenly, reflecting the complex behaviour of the unstable water surface. With a theoretical analysis we conclude that before the tip touches water surface, two water profiles appear, one stable and the other unstable. Then, with further approaching, the tip touches water surface and the non-contact to contact transition occurs. 相似文献
9.
Françoise Cornu 《Pramana》2005,64(5):785-801
The structure of equilibrium density profiles in an electrolyte in the vicinity of an interface with an insulating or conductive
medium is of crucial importance in chemical physics and colloidal science. The Coulomb interaction is responsible for screening
effects, and in dilute solutions the latter effects give rise to universal leading corrections to nonideality, which distinguish
electrolyte from nonelectrolyte solutions. An example is provided by the excess surface tension for an air-water interface,
which is determined by the excess particle density, and which was first calculated by Onsager and Samaras. Because of the
discrepancy between the dielectric constants on both sides of the interface, every charge in the electrolyte interacts with
an electrostatic image, and the Boltzmann factor associated with the corresponding self-energy has an essential singularity
over the length scalel from the wall. Besides Coulomb interactions, short-range repulsions must be taken into account in order to prevent the collapse
between charges with opposite signs or between each charge and its image when the solvent dielectric constant is lower than
that of the continuous medium on the other side of the interface. For a dilute and weaklycoupled electrolyte,l is negligible with respect to the bulk Debye screening length ξD. In the framework of the grand-canonical ensemble, systematic partial resummations in Mayer diagrammatics allow one to exhibit
that, in this regime, the exact density profiles at leading order are the same as if they were calculated in a partially-linearized
mean-field theory, where the screened pair interaction obeys an inhomogeneous Debye equation. In the latter equation the effective
screening length depends on the distancex from the interface: it varies very fast over the lengthl and tends to its bulk value over a few ξDs. The equation can be solved iteratively at any distancex, and the exact density profiles are calculated analytically up to first order in the coupling parameter l/ξD. They show the interplay between three effects: (1) the geometric repulsion from the interface associated with the deformation
of screening clouds, (2) the polarization effects described by the images on the other side of the interface, (3) the interaction
between each charge and the potential drop created by the electric layer which appears as soon as the fluid has not a charge-symmetric
composition. Moreover, the expressions allow us to go beyond Onsager-Samaras theory: the surface tension is calculated for
charge-asymmetric electrolytes and for any value of the ratio between the dielectric constants on both sides of the interface.
Similar diagrammatic techniques also allow one to investigate the charge renormalization in the dipolar effective pair interaction
along the interface with an insulating medium. 相似文献
10.
C. Humbert J.P. Decruppe 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):511-518
The optical and rheological properties of different viscoelastic solutions of surfactant are studied in order to gather experimental
data used to calculate the value of the stress optical coefficient C. Three surfactants of the same family (CTAB) have been chosen; they differ by the length of the hydrocarbon chain; it concerns
the dodecyltrimethylammonium bromide (C15H34BrN or DoTAB), the myristyltrimethylammonium bromide (C17H38BrN or MyTAB), and the hexadecyltrimethylammonium bromide (C19H42BrN or CTAB). Different parameters like the temperature of the solution and the salinity of the solvent have been made to
vary. Flow birefringence experiments and rheological measurements are performed on these solutions in order to study the dependence
of the extinction angle , of the birefringence intensity and of the shear stress with the shear rate . These data are used to check the stress optical law which turns out to be valid in a wide range of shear rates. The stress
optical coefficient C is then computed: it is found to vary with the salinity of the solvent and the temperature of the solution for a given surfactant.
Then, for all solutions of this work the variations of C are related to the variations of the polarizability anisotropy and the persistence length.
Received: 18 February 1998 / Revised: 23 June 1998 / Accepted: 22 July 1998 相似文献
11.
Th. Mühge A. Stierle N. Metoki H. Zabel U. Pietsch 《Applied Physics A: Materials Science & Processing》1994,59(6):659-665
High-quality thin Fe films were deposited on MgO(001) and Al2O3(1120) substrates in the thickness range from 7 to 50 nm. The structural properties have been studied by out-of-plane and in-plane X-ray scattering experiments. From the out-of-plane measurements the electron density profile was determined together with interface and surface roughness parameters. Fe on Al2O3 grows along the [110]-direction with a structural coherence length comprising about the total film thick ness and a very small mosaicity. From in-plane scattering experiments a three-domain structure was observed. On MgO(001) substrates Fe grows in the [001]-direction, with the Fe [100]-axis parallel to the MgO [110]-axis. On both substrates, the Fe films exhibit a very small surface and interface roughness, indicative for a high quality of the sputtered samples. 相似文献
12.
T. Kerle J. Klein K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):401-410
The capillary broadening of a 2-phase interface is investigated both experimentally and theoretically. When a binary mixture
in a thin film with thickness D segregates into two coexisting phases the interface between the two phases may form parallel to the substrate due to preferential
surface attraction of one of the components. We show that the interfacial profile (of intrinsic width w0) is broadened due to capillary waves, which lead to fluctuations, of correlation length of the local interface positions in the directions parallel to the confining walls. We postulate that acts as an upper cutoff for the spectrum of capillary waves on the interface, so that the effective mean square interfacial
width w varies as . In the limit of large D this yields or respectively for the case of short- or long-range forces between walls and the interface. We used the Nuclear Reaction Analysis
depth profiling technique, to investigate this broadening effect directly in two binary polymer mixtures. Our results reveal
that the interfacial width indeed increases with film thickness D, though the observed interfacial width is lower than the predicted w. This is probably due to surface tension effects imposed by the confining surfaces which are not taken into account in our
model.
Received: 19 February 1998 / Received in final form: 2 September 1998 / Accepted: 8 September 1998 相似文献
13.
Interface polarons in a realistic heterojunction potential 总被引:9,自引:0,他引:9
S.L. Ban J.E. Hasbun 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):453-461
The ground states of interface polarons in a realistic heterojunction potential are investigated by considering the bulk and
the interface optical phonon influence. A self-consistent heterojunction potential is used and an LLP-like method is adopted
to obtain the polaron effect. The numerical computation has been done for the Zn1-xCdxSe/ZnSe system to obtain the polaron ground state energy, self energy and effective mass parallel to the interface. A simplified
coherent potential approximation is developed to obtain the parameters of the ternary mixed crystal and the energy band offset
of the heterojunction. It is found that at small Cd concentration the bulk longitudinal optical phonons give the main contribution
for lower areal electron densities, whereas the interface phonon contribution is dominant for higher areal electron densities.
The interface polaron effect is weaker than the effect obtained by the three dimensional bulk phonon and by the two dimensional
interface phonon models.
Received 17 September 1998 相似文献
14.
M. Saglam A. Türüt Ç. Nuhoglu H. Efeoglu T. Kılıçoglu M.A. Ebeoglu 《Applied Physics A: Materials Science & Processing》1997,65(1):33-37
2 /p-Si MOS structures were prepared in 0.1 M K2SO4 electrolyte with a pH of 7 (the 0.1 M KOH solution was buffered with H2SO4) at current densities of 3, 5, and 7 mA/cm2 and with four different pH values of the electrolyte at 3 mA/cm2. It is found that thermal annealing at a relatively low temperature can be used to improve the anodic MOS characteristics.
Moreover, of the pH and current density it followed that the pH has a dominant role in the interface electrical properties.
The lowest interface state densities at the maximum and the midgap positions are 7.1×1011 and 2.7×1010 eV-1cm-2 for a sample made with pH=7, J=3 mA/cm2. The characteristics of this sample seem satisfactory for device applications of anodized p-Si.
Received: 8 July 1996/Accepted: 22 January 1997 相似文献
15.
W. Hanke O. Schmitt H. Endres R. Kleiner P. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):465-471
A quantitative analysis of a microscopic model for the intrinsic Josephson effect in high-temperature superconductors based
on interlayer tunneling is presented both within a mean-field BCS evaluation and a numerically essentially exact Quantum Monte-Carlo
study. The pairing correlations in the CuO2-planes are modelled by a 2D Hubbard model with attractive interaction, a model which accounts well for some of the observed
features such as the short planar coherence length. The stack of Hubbard planes is arranged on a torus, which is threaded
by a magnetic flux. The current perpendicular to the planes is calculated as a function of applied flux (i.e. the phase), and - after careful elimination of finite-size effects due to single-particle tunneling - found to display a
sinusoidal field dependence in accordance with interlayer Josephson tunneling. Studies of the temperature dependence of the
supercurrent reveal at best a mild elevation of the Josephson transition temperature compared to the planar Kosterlitz-Thouless
temperature. These and other results on the dependence of the model parameters are compared with a standard BCS evaluation.
Received: 24 February 1998 / Revised: 28 April 1998 / Accepted: 23 June 1998 相似文献
16.
A. Hübsch K. W. Becker 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):345-353
A very rich phase diagram has recently been found in CeCu2Si2 from
high pressure experiments where, in particular, a transition between an
intermediate valence configuration and an integral valent heavy fermion
state has been observed. We show that such a valence transition can be
understood in the framework of the periodic Anderson model. In particular,
our results show a breakdown of a mixed-valence state which is accompanied
by a drastic change in the f occupation in agreement with
experiment. This valence transition can possibly be interpreted as a
collapse of the large Fermi surface of the heavy fermion state which
incorporates not only the conduction electrons but also the localized
f electrons. The theoretical approach used in this paper
is based on the novel projector-based renormalization method (PRM). With
respect to the periodic Anderson model, the method was before only employed
in combination with the basic approximations of the well-known slave-boson
mean-field theory. In this paper, the PRM treatment is performed in a more
sophisticated manner where both mixed as well as integral valent solutions
have been obtained. Furthermore, we argue that the presented PRM approach
might be a promising starting point to study the competing interactions in
CeCu2Si2 and related compounds. 相似文献
17.
A model of deep and shallow traps has been applied in order to explain the temporal development of the signal wave amplification
as well as the pump wave depletion in two-wave-mixing experiments in the crystal Ba0.23Ca0.77TiO3 (BCT). The intensities of the outgoing waves have been studied at different intensities of the incident waves during the
first 500 s before the beams have reached their stable states. On the basis of the obtained temporal dependences of the intensities,
some material parameters of the crystal have been estimated, like excitation cross sections from the deep and shallow traps
(valence levels) into the conduction band, recombination rates from the conduction band into the valence levels, absolute
and redistributed charge densities of the deep and shallow traps, and modulations of the absorption and refractive indices.
Received: 26 May 2000 / Revised version: 26 September 2000 / Published online: 21 February 2001 相似文献
18.
J. Oberdisse 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):463-469
The transition from small to big unilamellar vesicles predicted by a Poisson-Boltzmann Cell Model for the thermodynamics of
a dilute phase of unilamellar charged vesicles is characterized. The radius as a function of experimental parameters is calculated
and the coexistence region of small and big vesicles is identified. We further investigate the physical meaning in terms of
simplified models, which allow for an identification of the role of parameters like the surface charge density or the Debye-length.
Connections to experiments are discussed.
Received: 20 October 1997 / Received in final form: 9 February 1998 / Accepted: 9 March 1998 相似文献
19.
M.T. Batchelor K.A. Seaton 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):719-725
On the basis of features observed in the exact perturbation approach solution for the eigenspectrum of the dilute A3 model, we propose expressions for excitations in the dilute A4 and A6 models. Principally, we require that these expressions satisfy the appropriate inversion relations. We demonstrate that they
give the expected E7 and E6 mass spectra, and universal amplitudes, and agree with numerical expressions for the eigenvalues.
Received: 17 February 1998 / Accepted: 30 April 1998 相似文献
20.
C.P. Wyss W. Lüthy H.P. Weber V.I. Vlasov Y.D. Zavartsev P.A. Studenikin A.I. Zagumennyi I.A. Shcherbakov 《Applied physics. B, Lasers and optics》1999,68(4):659-661
4 as a host for neodymium has several advantages for diode pumping in comparison with other crystals. The absorption cross
section of neodymium in GdVO4 is considerably stronger and broader than in YAG. This allows for the construction of very compact monolithical microchip
lasers. In our paper, we report for the first time on a diode-pumped monolithical Nd3+([%at.]1.3):GdVO4 microchip laser at 1.06 μm. A maximum output power of 5 W is achieved. The temporal and the spectral emission properties
are described. The beam propagation properties are studied in detail.
Received: 23 July 1998 / Revised version: 9 November 1998 / Published online: 24 February 1999 相似文献