共查询到20条相似文献,搜索用时 15 毫秒
1.
C. Lorthioir P. Auroy B. Deloche Y. Gallot 《The European physical journal. E, Soft matter》2002,7(3):261-266
The chain segment dynamics in the bulk lamellar phase of polystyrene-polydimethylsiloxane (PS-PDMS) block copolymers has been
probed by NMR. The experiments were performed on a PS-PDMS diblock and on a PS-PDMS-PS triblock with twice the molecular weight.
In the diblock, at room temperature, the PDMS block segments undergo uniaxial reorientations around the normal to the lamellae.
In the triblock, the reorientational motions exhibit a lower degree of symmetry: deviations from a uniaxial dynamics are observed.
Such a behaviour originates in the anchorage of both PDMS chain ends into the PS glassy layers.
Received 27 September 2001 and Received in final form 18 January 2002 相似文献
2.
A. B. Croll M. W. Matsen A. -C. Shi K. Dalnoki-Veress 《The European physical journal. E, Soft matter》2008,27(4):407-411
In the ordered state, symmetric diblock copolymers self-assemble into an anisotropic lamellar morphology. The equilibrium
thickness of the lamellae is the result of a delicate balance between enthalpic and entropic energies, which can be tuned
by controlling the temperature. Here we devise a simple yet powerful method of detecting tiny changes in the lamellar thickness
using optical microscopy. From such measurements we characterize the enthalpic interaction as well as the kinetics of molecules
as they hop from one layer to the next in order to adjust the lamellar thickness in response to a temperature jump. The resolution
of the measurements facilitate a direct comparison to predictions from self-consistent field theory. 相似文献
3.
An original, quantitative, theory of “living” radical copolymerization has been developed proceeding from the current concepts
of its kinetics and mechanism. This theory enables one to calculate both the dependence of monomers' conversion on time and
any statistical characteristics of the chemical structures of the copolymers formed. Expressions have been derived describing
the angular dependence of the scattering amplitude of the copolymerization products. The results of quantitative calculations
of these characteristics have been also presented to exemplify the potentialities of the theory.
Received 13 February 2001 and Received in final form 4 February 2002 相似文献
4.
V.Yu. Irkhin M.I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):401-408
The longitudinal and transverse nuclear magnetic relaxation rates 1/T
1(T) and 1/T
2(T) are calculated for three- and two-dimensional (3D and 2D) metallic ferro- and antiferromagnets (FM and AFM) with localized
magnetic moments in the spin-wave temperature region. The contribution of the one-magnon decay processes is strongly enhanced
in comparison with the standard T-linear Korringa term, especially for the FM case. For the 3D AFM case this contribution diverges logarithmically, the divergence
being cut at the magnon gap ω due to magnetic anisotropy, and for the 2D AFM case as ω-1. The electron-magnon scattering processes yield T
2ln(T/ω) and T
2/ω1/2-terms in 1/T
1 for the 3D AFM and 2D FM cases, respectively. The two-magnon (“Raman”) contributions are investigated and demonstrated to
be large in the 2D FM case. Peculiarities of the isotropic 2D limit (where the correlation length is very large) are analyzed.
Received 29 November 1999 and Received in final form 6 June 2000 相似文献
5.
R. Lefort A. Hédoux Y. Guinet E. Cochin M. Descamps 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):519-525
The first analysis of rapid intramolecular motions of triphenyl phosphite by 2H NMR is presented. The fragile slowing down of the primary relaxation is followed by a solid-echo method. The occurrence
of a fast reorientation of the phenyl side groups is demonstrated in the supercooled liquid state, identified as a two-fold
flip on the basis of simple lineshape simulations. Coexistence of both static and motionally averaged components in “two phase”
spectra indicate a broad distribution of correlation times for this relaxation. This dynamical behavior is shown to persist
in the glacial phase.
Received 28 May 2002 / Received in final form 1st October 2002
Published online 31 December 2002 相似文献
6.
Shangwu Ding C.A. McDowell Chaohui Ye Mingsheng Zhan Xiwen Zhu Kelin Gao Xianping Sun Xi-An Mao Maili Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):23-35
Magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) spectroscopy is shown to be a promising technique
for implementing quantum computing. The theory underlying the principles of quantum computing with nuclear spin systems undergoing
MAS is formulated in the framework of formalized quantum Floquet theory. The procedures for realizing state labeling, state
transformation and coherence selection in Floquet space are given. It suggests that by this method, the largest number of
qubits can easily surpass that achievable with other techniques. Unlike other modalities proposed for quantum computing, this
method enables one to adjust the dimension of the working state space, meaning the number of qubits can be readily varied.
The universality of quantum computing in Floquet space with solid state NMR is discussed and a demonstrative experimental
implementation of Grover's search is given.
Received 19 April 2001 相似文献
7.
The subject of this paper is inspired by microphase-separated copolymer melts in which a small-scale structure is present
inside one of the phases of a large-scale structure. Such a situation can arise in a diblock copolymer melt, if one of the
blocks of the diblock is in itself a multiblock copolymer or a comb copolymer. Due to the presence of the large-scale structure,
the chains are stretched. The aim of this paper is to investigate the influence of this chain stretching on the formation
of the small-scale structure. To gain insight we study infinite melts of infinitely long copolymer chains that are subjected
to a stretching force. For melts of monodisperse multiblock copolymers we find that the stretching destabilizes the homogeneous
phase. If the stretching is strong, the lamellar structure is the only stable structure. The periodicity increases with the
degree of stretching. For melts of monodisperse comb copolymers the chain stretching has no influence on the stability of
the homogeneous phase. If the stretching is strong, the lamellar structure and the hexagonal structure are the only stable
structures. The periodicity is independent of the degree of stretching. For the multiblock copolymer we investigated the influence
of block length polydispersity. For small polydispersity the period of the structure increases monotonically with the degree
of stretching. For intermediate polydispersity, the period initially decreases before it starts to increase. For large polydispersity, the mean-field period at the spinodal is infinite, becoming finite
once the stretching force exceeds some critical value. For very large polydispersity the mean-field period at the spinodal
remains infinite for any value of the stretching force.
Received: 14 February 2002 / Accepted: 24 March 2003 / Published online: 29 April 2003
RID="a"
ID="a"e-mail: hindrik.angerman@abp.nl 相似文献
8.
The effect of polydispersity on an AB diblock copolymer melt is investigated using lattice-based Monte Carlo simulations.
We consider melts of symmetric composition, where the B blocks are monodisperse and the A blocks are polydisperse with a Schultz-Zimm
distribution. In agreement with experiment and self-consistent field theory (SCFT), we find that polydispersity causes a significant
increase in domain size. It also induces a transition from flat to curved interfaces, with the polydisperse blocks residing
on the inside of the interfacial curvature. Most importantly, the simulations show a relatively small shift in the order-disorder
transition (ODT) in agreement with experiment, whereas SCFT incorrectly predicts a sizable shift towards higher temperatures. 相似文献
9.
Using self-consistent field theory (SCFT), we investigate the morphologies formed by a melt brush of AB diblock copolymers
grafted to a flat substrate by their B ends. In addition to a laterally uniform morphology, SCFT predicts three ordered morphologies
exhibiting different periodic patterns at the air surface: a hexagonal array of A-rich dots, an alternating sequence of A-
and B-rich stripes, and a hexagonal pattern of B-rich dots. When the phase diagram of the tethered film is plotted as a function
of A/B incompatibility,
N , and diblock composition, f , it resembles the bulk phase diagram with the periodic phases converging to a mean-field critical point at weak segregation.
The periodic-phase region in the phase diagram shrinks with increasing grafting density and expands when the air surface acquires
an affinity for the grafted B blocks. 相似文献
10.
Aqueous solutions of a well-defined poly(N-isopropylacrylamide-co-sodium 2-acrylamido-methylpropanesulfonate) (NIPAM/NaAMPS in a 95/5 molar ratio) have been investigated by means of small-angle
neutron scattering (SANS) and rheological experiments as a function of temperature ( 25°
C
T
60°
C) and polymer concentration ( 0.5wt%
C
12wt%). The solutions remain optically transparent and isotropic over the whole temperature range, in contrast with the homopolyNIPAM
which precipitates above its lower critical solution temperature (LCST = 32°
C). Upon addition of salt, the systems undergo a micro-macrophase separation. At temperatures above 45°
C, the SANS spectra exhibit a sharp peak at a scattering wave vector, q
max, which increases slightly with temperature. At high temperature ( T∼ 60°
C), the scattered intensity follows a power law I(q) ∼q
-4 in the asymptotic regime, characteristic of two-density media with sharp interfaces, and q
max is found to vary with polymer concentration as q
max∼C
0.22. Estimates of the typical sizes give values between 40 ? and 200 ?. These results provide a strong evidence of a thermally
induced microphase separation, which is corroborated by the very sharp increases of the viscosity (over 2 decades) and of
the stress relaxation time of the solutions, occurring in the temperature range where the scattering peak is observed. The
results are discussed and compared with the theoretical models proposed for weakly charged polyelectrolytes in a poor solvent.
Received 1 October 2001 相似文献
11.
Matsen MW 《The European physical journal. E, Soft matter》2006,21(3):199-207
We investigate the effect of polydispersity on the lamellar phase of a diblock copolymer melt using self-consistent field
theory (SCFT). A previous SCFT calculation predicted that polydispersity increases the domain spacing consistent with experiment,
but it also suggested that the effect vanishes with increasing segregation contrary to experiment. We attribute this disagreement
to a problem of slow convergence of the Gaussian-quadrature technique used to integrate over the molecular-weight distribution
when either the segregation or polydispersity index is large. Here the problem is overcome by a new efficient algorithm that
allows high-order quadratures for relatively little computational cost. When implemented, we find that the elevated domain
spacing does indeed persist into the strong-segregation regime consistent with experiment. This conclusion is also substantiated
by the analytical strong-segregation theory (SST). 相似文献
12.
A. Carvalho P.J. Sebastião A. Ferraz A.C. Ribeiro H.T. Nguyen 《The European physical journal. E, Soft matter》2000,2(4):351-358
In this work we present a proton NMR comparative study of the molecular order in the smectic C2 (), smectic C^* () and anticlinic smectic C phases ( and ) of two liquid crystalline compounds. The second moments of the experimental proton NMR spectra are well explained taking
into account two different molecular orientations models. From the analysis of our experimental results it was possible to
estimate the tilt angles for all the smectic C phases studied in this work.
Received 15 September 1999 and Received in final form 18 January 2000 相似文献
13.
M. Winkelmann G. Fischer B. Pilawa E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):199-209
Nuclear magnetic resonance (NMR) and relaxation of 63Cu and 65Cu in a powder sample of the heavy-fermion paramagnet CeCu6 is measured and analysed quantitatively. Five different Cu sites are accessible to a detailed analysis. We derive quadrupolar
splitting frequencies, Ce to Cu transferred hyperfine field coupling constants, and transversal as well as longitudinal relaxation
behaviour. Only small relaxation anomalies are observed at the orthorhombic to monoclinic structural phase transition of CeCu6. We point to the different importance of transferred hyperfine interaction and local conduction electron density for static
or dynamic part, respectively, of Cu hyperfine interaction. The different sign of the transferred hyperfine interaction from
Ce3+ to different Cu neighbours reveals the different competing interaction mechanisms, giving rise to the heavy-fermion paramagnetic
behavior of CeCu6.
Received 20 November 2001 相似文献
14.
Poivet S Fabre P Nallet F Schierholz K Abraham G Papon E Gnanou Y Ober R Guerret O El-Bounia NE 《The European physical journal. E, Soft matter》2006,20(3):273-287
We study asymmetric block copolymers with the simple diblock AB architecture, in the case where the longer block A is both
hydrophobic and “soft”, whereas the shorter block B is hydrophilic and “hard”. Materials with such a particular combination
of physico-chemical and mechanical properties have distinctive advantages, in particular for designing water-compatible adhesive
materials. The phase diagram is established, combining NMR and SAXS characterisations of the materials. The swelling with
water is monitored through gravimetry and “time-resolved” SAXS. Indications of maintained adhesive properties in a wet environment
are given. 相似文献
15.
R. Dimova U. Seifert B. Pouligny S. Förster H.-G. Döbereiner 《The European physical journal. E, Soft matter》2002,7(3):241-250
Giant vesicles prepared from the diblock copolymer polybutadien-b-polyethyleneoxide (PB-PEO) exhibit a shear surface viscosity,
which is about 500 times higher than those found in common phospholipid bilayers. Our result constitutes the first direct
measurement of the shear surface viscosity of such polymersomes. At the same time, we measure bending and stretching elastic
constants, which fall in the range of values typical for lipid membranes. Pulling out a tether from an immobilized polymersome
and following its relaxation back to the vesicle body provides an estimate of the viscous coupling between the two monolayers
composing the polymer membrane. The detected intermonolayer friction is about an order of magnitude higher than the characteristic
one for phospholipid membranes. Polymersomes are tough vesicles with a high lysis tension. This, together with their robust
rheological properties, makes them interesting candidates for a number of technological applications.
Received 2 March 2001 and Received in final form 15 February 2002 相似文献
16.
E. Kerscher M.T. Kelemen K.H. Diefenbach O. Stockert H. v. Löhneysen E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):241-247
Single-crystal like nuclear magnetic resonance spin-echo spectra are obtained for powder samples of the antiferromagnet CeCu5Au in the paramagnetic phase. Line shifts and quadrupolar splittings are analyzed for 63Cu and 65Cu. The influence of the extreme magnetic anisotropy of the CeCu6-xAux compounds on nuclear spin relaxation is discussed.
Received 19 June 2000 相似文献
17.
R. Khomeriki 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):99-103
The route to and from the chaos via period doubling bifurcations in nuclear spin system with dipole-dipole interactions is investigated. The transition points
are found. It is shown that route from the chaos proceeds according the Feigenbaum scenario.
Received 19 August 1998 and Received in final form 15 December 1998 相似文献
18.
The shear-induced ordering of lamellar and gyroid structures of a nonionic surfactant C16E7/D2O system in a Couette shear cell ( 0.001 < < 10 s-1, : shear rate) has been investigated by using a small angle neutron scattering technique. In the lamellar phase, the steady
shear flow having > 0.01 s-1 suppresses undulation fluctuations of lamellae (Maxwell effect). This suppression of fluctuations brings two effects; 1)
shear-induced lamellae ordering toward a parallel orientation and 2) obstruction of a lamellar↦gyroid transition. It is quite
interesting to note that there is a characteristic shear rate range ( 0.01 < < 0.3 s-1), where both effects take place. We have also investigated the shear effects on the gyroid phase. Below the characteristic
shear rate range, the gyroid structure keeps three-dimensional network lattice, while above the characteristic shear rate
range, the gyroid structure transforms to the parallel orientation lamellae (shear-induced gyroid-lamellar transition). Thus
the shear flow having the characteristic shear rate plays very important roles in shear ordering phenomena.
Received 26 June 2000 and Received in final form 12 January 2001 相似文献
19.
We study the cylinder to sphere morphological transition of diblock copolymers in aqueous solution with a hydrophobic block
and a charged block. We find a metastable undulated cylinder configuration for a range of charge and salt concentrations which,
nevertheless, occurs above the threshold where spheres are thermodynamically favorable. By modeling the shape of the cylinder
ends, we find that the free-energy barrier for the transition from cylinders to spheres is quite large and that this barrier
falls significantly in the limit of high polymer charge and low solution salinity. This suggests that observed undulated cylinder
phases are kinetically trapped structures. 相似文献
20.
R. Decressain L. Carpentier E. Cochin J. P. Amoureux 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):223-230
In this contribution we report on the plastic crystal 1-chloroadamantane
dynamics via conventional frequency dependent (1H and 13C) and
field cycling NMR measurements. A suitable microscopic dynamical model,
worked out from from X-ray analysis is developed and the molecular motions
are interpreted in terms of: self diffusion and dipolar molecular axis
combined with uniaxial rotation. In the rotator phase the molecules execute
a bimodal reorientation process whereas the uniaxial rotation solely
persists in the low temperature phase. In both phases, the residence times
exhibit an Arrhenius temperature dependence. The results confirm the
existence of a dynamic crossover transition predicted by molecular dynamics
simulation. 相似文献