共查询到20条相似文献,搜索用时 31 毫秒
1.
Hutchings LR Richards RW Thompson RL Bucknall DG 《The European physical journal. E, Soft matter》2002,8(2):121-128
High-molecular-weight heterotelechelic deuteriopolystyrene, NDPSF, possessing an amine functional group at one end of the
chain and a fluorocarbon group at the other was tethered to a silicon substrate by its amine functional group. These layers
were coated with an unfunctionalised polystyrene matrix, HPS, such that the total film thickness covered a range from 2.2
to 9 times the radius of gyration of NDPSF. The detailed distribution of the polymers after annealing for times much greater
than the reptation period of either of the components, was obtained using neutron reflectometry. No evidence for bridging
of the two interfaces was found for the thicker films, but the finite concentration of the NDPSF polymer observed for the
thinnest films may be due to bridging since the energy gain of the fluorocarbon end is just greater than the loss due to configurational
entropy losses. A linear increase in the ellipsometric thickness of the excess of NDPSF at the substrate was discovered and
we attribute this to the NDPSF slowly being leached out of the layer initially at the substrate followed by diffusion into
the bulk of the film. The concentration profiles obtained are consistent with hindered relaxation of the large NDPSF molecules,
when they are tethered at the substrate or at the vacuum surface.
Received 21 August 2001 and Received in final form 7 January 2002 相似文献
2.
A. Brioude F. Lequevre J. Mugnier C. Bovier J. Dumas J.C. Plenet 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):115-119
Very thin ZrO
2
films (few nanometers) have been prepared by sol-gel process. These films were deposited onto a stack of a thin silver layer
evaporated on a glass substrate for Surface Plasmons Resonance (SPR) experiments. The first aim of this work is to study the
high densification of the sol-gel films followed by the refractive index and thickness accurate measurements at each step
of the annealing procedure, using an optical set-up based on SPR. Secondly, SPR excitation coupled with micro-Raman experiment
has also been performed to determine the thin films structure depending on layer thickness. Finally, Conventional Transmission
Electron Microscopy (CTEM) and High Resolution (HRTEM) studies have been conducted to check and complete Raman spectroscopy
results. A discussion compares the optical results and the Transmission Electron Microscopy observations and shows that ultra
thin layers structure is strongly depends on films thickness.
Received 14 May 2001 and Received in final form 2 January 2002 相似文献
3.
Kostakis K Mourmouris S Charalabidis D Pitsikalis M 《The European physical journal. E, Soft matter》2003,10(1):55-63
Linear polyisoprenes having dimethylamine end groups were prepared by high vacuum anionic polymerization techniques using
3-dimethylaminopropyllithium as the initiator. The amine group was reacted with 2-cholesteryl-2-oxo-1,3,2-dioxaphospholane
to provide polymer chains having end zwitterionic groups chemically connected with cholesterol. The association behavior of
these end-functionalized polymers was studied in cyclohexane by low angle laser light scattering, dynamic light scattering,
and viscometry. The aggregation numbers, N
w were found to decrease by increasing the molecular weight of the precursor polymer, due to excluded volume repulsions. The
ability of cholesterol to form liquid crystal mesophases facilitated the association process leading to higher N
w values. The hydrodynamic behavior of the aggregates was similar to that of star polymers. The dependence of the N
w values on the molecular weight of the base polymer, the polydispersity of the associates and the absence of critical micelle
concentration, cmc are compatible with the linear head-packing model.
Received 29 April 2002 and Received in final form 13 November 2002 Published online: 11 March 2003 相似文献
4.
Higgins AM Sferrazza M Jones RA Jukes PC Sharp JS Dryden LE Webster J 《The European physical journal. E, Soft matter》2002,8(2):137-143
We investigate the dynamics of spinodal dewetting in liquid-liquid polymer systems. Dewetting of poly(methyl-methacrylate)
(PMMA) thin films on polystyrene (PS) “substrates” is followed in situ using neutron reflectivity. By following the development of roughness at the PS/PMMA interface and the PMMA surface we extract
characteristic growth times for the dewetting process. These characteristic growth times are measured as a function of the
molecular weight of the two polymers. By also carrying out experiments in the regime where the dynamics are independent of
the PS molecular weight, we are able to use dewetting to probe the scaling of the PMMA thin film viscosity with temperature
and molecular weight. We find that this scaling reflects bulk behaviour. However, absolute values are low compared to bulk
viscosities, which we suggest may be due in part to slippage at the polymer/polymer interface.
Received 25 June 2001 and Received in final form 5 December 2001 相似文献
5.
Hartmann L Gorbatschow W Hauwede J Kremer F 《The European physical journal. E, Soft matter》2002,8(2):145-154
The molecular dynamics in thin films (18 nm-137 nm) of isotactic poly(methyl methacrylate) (i-PMMA) of two molecular weights
embedded between aluminium electrodes are measured by means of dielectric spectroscopy in the frequency range from 50 mHz
to 10 MHz at temperatures between 273 K and 392 K. The observed dynamics is characterized by two relaxation processes: the
dynamic glass transition (α-relaxation) and a (local) secondary β-relaxation. While the latter does not depend on the dimensions
of the sample, the dynamic glass transition becomes faster (≤2 decades) with decreasing film thickness. This results in a
shift of the glass transition temperature T
g to lower values compared to the bulk. With decreasing film thickness a broadening of the relaxation time distribution and
a decrease of the dielectric strength is observed for the α-relaxation. This enables to deduce a model based on immobilized
boundary layers and on a region displaying a dynamics faster than in the bulk. Additionally, T
g was determined by temperature-dependent ellipsometric measurements of the thickness of films prepared on silica. These measurements
yield a gradual increase of T
g with decreasing film thickness. The findings concerning the different thickness dependences of T
g are explained by changes of the interaction between the polymer and the substrates. A quantitative analysis of the T
g shifts incorporates recently developed models to describe the glass transition in thin polymer films.
Received 12 August 2001 and Received in final form 16 November 2001 相似文献
6.
Y.P. Lee K.W. Kim Y.V. Kudryavtsev V.V. Nemoshkalenko B. Szymański 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):41-50
Comparative study of the solid-state reaction (SSR) in a series of Ti/Ni multilayered films (MLF) with a bilayer period of
0.65-22.2 nm and a constant Ti to Ni sublayer thickness ratio has been performed by using the experimental and computer-simulated
magneto-optical (MO) and optical spectroscopies as well as X-ray diffraction (XRD). It was shown that alloyed-like regions
in an amorphous structure is spontaneously formed near the interfaces between pure elements during the film deposition. The
thickness of this region was estimated as 2-3.8 nm on the basis of the MO and optical studies. The SSR in the Ti/Ni MLF caused
by an annealing at 580 K for 60 min increases the thickness of these interfacial amorphous regions. It was shown that SSR
takes place mainly in the Ti/Ni MLF with relatively “thick” sublayers. The existence of a threshold nominal Ni-sublayer thickness
for observing the equatorial Kerr effect of about 3.0 and 4.5 nm for the as-deposited and annealed Ti/Ni MLF, respectively,
is explained by formation of the nonmagnetic alloyed regions between pure components during the film deposition as a result
of the SSR. For the case of Ti/Ni MLF, the MO and optical approaches turn out to be more sensitive in determining the thickness
of the reacted zone, while XRD is more useful for the structural analysis. It was also shown that the very thin nonreacted
Ni sublayers have different MO properties (and hence electronic structure) from the bulk.
Received 2 May 2001 and Received in final form 21 November 2001 相似文献
7.
M.A. Gilmore B.L. Johnson 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):297-305
We study the effects of layer thickness variations on the collective plasmon excitation modes of finite superlattices. Unlike
other symmetry lowering mechanisms, thickness variation does not strongly localize the surface modes. We find that the reason
for this insensitivity lies in the fact that the collective modes of a given finite structure must evolve continuously from
the single-finite-superlattice at zero thickness deviation into modes of a pair of uncoupled finite structures at large thickness
variation. We also show that this behavior is analogous to the evolution of molecular orbitals from atomic orbitals as the
internuclear separation is reduced, in contrast to the analogy of the superlattice modes as a stack of coupled quantum wells.
This emphasizes the difference between the electromagnetic symmetry of the finite superlattice and the structural symmetry.
Received 16 April 2001 and Received in final form 6 July 2001 相似文献
8.
M.C.P. van Eijk M. Bergsma S.-J. Marrink 《The European physical journal. E, Soft matter》2002,7(4):317-324
The association behaviour of a number of glucitol amine gemini surfactants has been investigated by means of molecular dynamics
and self-consistent-field calculations. We have shown that the titratable head group of the surfactant is responsible for
a micelle-to-membrane transition when changing the pH. Furthermore, the association structure of this group of surfactants is shown to be very sensitive to ionic strength. The
combination of a charged head group, a spacer, and the hydrophilic glucitol side chains is responsible for the possible structural
transitions in the associates as a function of ionic strength and pH.
Received: 12 January 2002 and Received in final form 10 March 2002 相似文献
9.
Ngai KL 《The European physical journal. E, Soft matter》2002,8(2):225-235
Large increases of mobility of local segmental relaxation observed in polymer films as the film thickness is decreased, as
evidenced by decreases of the glass temperature, are not found for relaxation mechanisms that have longer length scales including
the Rouse relaxation modes and the diffusion of entire polymer chains. We show that the coupling model predictions, when extended
to consider polymer thin films, are consistent with a large increase of the mobility of the local segmental motions and the
lack of such a change for the Rouse modes and the diffusion of entire polymer chains. There are two effects that can reduce
the coupling parameter of the local segmental relaxation in thin films. One is the chain orientation that is induced parallel
to the surface when the film thickness h becomes smaller than the end-to-end distance of the chains and the other is a finite-size effect when h is no longer large compared to the cooperative length scale. Extremely thin ( ≈ 1.5 nm) films obtained by intercalating a
polymer into layered silicates have thickness significantly less than the cooperative length scale near the bulk polymer glass
transition temperature. As a result, the coupling parameter of the local segmental relaxation in such thin films is reduced
almost to zero. With this plausible assumption, we show the coupling model can explain quantitatively the large decrease of
the local segmental relaxation time found experimentally.
Received 1 August 2001 and Received in final form 1 December 2001 相似文献
10.
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
11.
A. Mougin C. Dufour N. Maloufi K. Dumesnil Ph. Mangin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):289-296
Single crystal RFe2(110) films were grown by molecular beam epitaxy to a total thickness of 1000 ? at different substrate temperatures ranging
from 450
°
C to 660
°
C. The first stages of growth and the surface morphology of the deposited layers have been studied using Reflection High Energy
Electron Diffraction (RHEED) and Atomic Force Microscopy (AFM). The growth is first strained but further deposit induces the
formation of three-dimensional fully relaxed islands. Subsequently, the morphology of the RFe2(110) nanosystems evolves from anisotropic dots to a smooth surface, as a function of the preparation parameters, i.e. nominal thickness and substrate temperature. It also depends on the rare earth involved in the compound.
Received 29 June 2000 相似文献
12.
We study the low-velocity (0.1-100 μm s-1) frictional properties of interfaces between a rough glassy polymer and smooth silanized glass, a configuration which gives
direct access to the rheology of the adhesive joints in which shear localizes. We show that these joints exhibit the full
phenomenology expected for confined quasi-2D soft glasses: they strengthen logarithmically when aging at rest, and weaken
(rejuvenate) when sliding. Rejuvenation is found to saturate at large velocities. Moreover, aging at rest is shown to be strongly
accelerated when waiting under finite stress below the static threshold.
Received 20 February 2002 and Received in final form 16 May 2002 相似文献
13.
G. Strobl 《The European physical journal. E, Soft matter》2000,3(2):165-183
Based on broad and detailed evidence from a large variety of experiments on several polymer systems carried out by other authors
and ourselves, a novel concept for understanding the crystallization of polymers from the melt is developed. The experiments
generally indicate that the formation and growth of the lamellar crystallites is a multi-step process passing over intermediate
states. We suggest a specific route which is compatible with the observations. It is proposed that the initial step is always
the creation of a mesomorphic layer which spontaneously thickens, up to a critical value, where it solidifies through a cooperative
structural transition. The transition produces a granular crystalline layer, which transforms in the last step into homogeneous
lamellar crystallites. The model leads to predictions about the temperature dependencies of the crystal thickness and the
growth rate which are at variance with conventional views but in agreement with findings in recent experiments.
Received 17 February 2000 and Received in final form 30 March 2000 相似文献
14.
S. Kutter E.M. Terentjev 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):455-462
Twist-storing polymers respond with elastic energy penalty to coherent or random twisting along the local chain axis away
from its equilibrium, which can be straight (as in “ribbons”) or helical (as in DNA and other biopolymers). Here we study
the equilibrium conformation of such polymers, focusing on the thermodynamic balance between twist and writhe, resulting from
the competition between the random coil entropy and the potential energy stored in superhelical portions of the polymer chain.
Two macroscopic variables characterise such a chain, the end-to-end distance R and the link number Lk, which is a topological invariant of a given polymer with clamped ends. We find that with increasing link number Lk, the chain accommodates its excess twist in growing plectonemes, unless forced out of this state by stretching its end-to-end
distance R. We calculate the force-extension relation, which exhibits crossovers between different deformation regimes.
Received 16 November 2000 and Received in final form 6 February 2001 相似文献
15.
T. Salditt C. Li A. Spaar U. Mennicke 《The European physical journal. E, Soft matter》2002,7(2):105-116
We have investigated the structure of solid-supported, multilamellar membranes by X-ray reflectivity. The density profile
is obtained by fitting the full q-range to a model using the bilayer Fourier coefficients as fitting parameters. The effect of hydration and the substrate
boundary condition are discussed in view of the well-known Landau-Peierls effect and its implications for structure determination.
The resulting bilayer density profile agrees remarkably well with previously published data of a molecular dynamics (MD) simulation
for 1,2-oleoyl-palmitoyl-sn-glycero-3-phosphocholine (OPPC).
Received 1 October 2001 and Received in final form 21 December 2001 相似文献
16.
The branched crystal morphology of linear polyethylene formed at various temperatures from thin films has been studied by
atomic-force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) pattern and polymer decoration
technique. Two types of branched patterns, i.e. dendrite and seaweed patterns, have been visualized. The fractal dimension d
f = 1.65 of both dendrite and some of seaweed patterns was obtained by using the box-counting method, although most of the
seaweed patterns are compact. Selected-area ED patterns indicate that the fold stems tilt about 34.5° around the b-axis and polymer decoration patterns show that the chain folding direction and regularity in two (200) regions are quite
different from each other. Because of chain tilting, branched crystals show three striking features: 1) the lamella-like branches
show two (200) regions with different thickness; 2) the crystals usually bend towards the thin region; 3) the thick region
grows faster by developing branches, thus branches usually occur outside the thick region. The branched patterns show a characteristic
width w, which gives a linear relationship with the crystallization temperature on a semilogarithmic plot.
Received 15 March 2002 and Received in final form 29 April 2002 相似文献
17.
P.G. de Gennes 《The European physical journal. E, Soft matter》2002,7(1):31-34
When a glassy polymer film is formed by evaporation, the region near the free surface is polymer rich and becomes glassy first,
as noticed long ago by Scriven et al. We discuss the thickness of this “crust” and the time interval where it is present --before freezing of the whole film. We
argue that the crust is under mechanical tension, and should form some cracks. This may be the source of the roughness observed
on the final, dry films, when the solvent vapor pressure is high (and leads to thin crusts).
Received 13 November 2001 相似文献
18.
W. Christen U. Even 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):87-90
This contribution addresses the inelastic interaction of positively charged molecular cluster ions with a solid surface at
kinetic energies up to 30 eV/molecule. We report experimental results on the scattering of mass-selected, protonated methanol
cluster cations (CH3OH)nH+, n = 4-32, off a diamond-coated silicon surface. In particular we provide fragment size distributions of methanol cluster ions
following their impact on the target, as well as surface-induced neutralization probabilities of methanol cluster ions as
a function of the size and the kinetic energy of the parent clusters.
Received 30 November 2000 相似文献
19.
A. Fedorus V. Koval A. Naumovets H. Pfnür 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):395-403
Ordering of dysprosium on Mo(112) up to 1.5 monolayers has been investigated by LEED and work function analysis after adsorption
at 100 K and annealing between 200 and 1000 K. At low annealing temperatures (< 350-600 K) ordered structures are found, which
are changed or even destroyed irreversibly by annealing steps to higher temperatures. At coverages, θ, up to 0.3 monolayer
a (6×1) not strictly commensurate chain structure is seen, which coexists up to θ = 0.58 with a one-dimensionally incommensurate
c( 1.56×2) structure. At higher coverages up to the physical monolayer at θ≈ 0.77, incommensurate ( n×2) followed by oblique ( n×1) structures are seen with n continuously variable with coverage. The second layer forms a p (1.33×1) structure. Annealing to higher temperatures causes
irreversible structural transitions with strongly coverage dependent properties. Up to θ = 0.58, only a glass-like disordered
phase is formed, which cannot be ordered again. In contrast, the rectangular incommensurate structures between 0.58 < θ <
0.68 remain unchanged upon annealing, whereas the structures at higher coverages and those of the second layer are transformed
into commensurate (s×1) structures with integer s. Geometrical models are presented for the non-annealed structures and possible origins for the two-dimensional concentration
dependent vitrification of the Dy layers are discussed.
Received 15 June 2001 相似文献
20.
We present an extensive experimental study and scaling analysis of friction of gelatin gels on glass. At low driving velocities,
sliding occurs via propagation of periodic self-healing slip pulses whose velocity is limited by collective diffusion of the
gel network. Healing can be attributed to a frictional instability occurring at the slip velocity V = V
c. For V > V
c, sliding is homogeneous and friction is ruled by the shear-thinning rheology of an interfacial layer of thickness of order
the (nanometric) mesh size, containing a solution of polymer chain ends hanging from the network. In spite of its high degree
of confinement, the rheology of this system does not differ qualitatively from known bulk ones. The observed ageing of the
static friction threshold reveals the slow increase of adhesive bonding between chain ends and glass. Such structural ageing
is compatible with the existence of a velocity-weakening regime at velocities smaller than V
c, hence with the existence of the healing instability.
Received: 7 March 2003 / Accepted: 2 May 2003 / Published online: 11 June 2003
RID="b"
ID="b"e-mail: ronsin@gps.jussieu.fr 相似文献