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1.
We study large scale surface deformations of a liquid film
unstable due to the Marangoni effect caused by external heating
on a smooth and solid substrate. The work is based on the thin
film equation which can be derived from the basic hydrodynamic
equations. To prevent rupture, a repelling disjoining pressure
is included which accounts for the stabilization of a thin
precursor film and so prevents the occurrence of completely dry
regions. Linear stability analysis, nonlinear stationary
solutions, as well as three-dimensional time dependent numerical
solutions for horizontal and inclined substrates reveal a rich
scenario of possible structures for several realistic fluid
parameters. 相似文献
2.
Carvalho AJ Pereira-da-Silva MA Faria RM 《The European physical journal. E, Soft matter》2006,20(3):309-315
Self-organized block copolymer structures derived from dewetting of thin films are becoming important in nanotechnology because
of the various spontaneous and regular sub-micrometric surface patterns that may be obtained. Here, we report on the self-organization
of a poly(styrene)-b-poly(ethene-co-butene-1)-b-poly(styrene) triblock copolymer during drying of its solution over a mica
substrate. Regular submicrometric arrangements with long-range order were formed at critical polymer concentrations, consisting
of parallel ribbons and hexagonal arrays of dots (droplets). This variety of highly ordered structures is explained by the
interplay between forming mechanisms, mainly due to “fingering instabilities” at the three-phase line of the copolymer solution
during drying. The thickness of the structures was “quantized” due to the microphase separation of the block copolymer. The
formation of hexagonal patterns may be attributed to Marangoni instability at the liquid film surface prior to dewetting. 相似文献
3.
We study the dewetting of thin polymer films deposited on slippery substrate. Recent experiments on these systems have revealed
many unexpected features. We develop here a model that takes into account the rheological properties of polymer melts, focussing
on two dewetting geometries (the receding of a straight edge, and the opening of a hole). We show that the friction law associated
with the slippage between the film and the substrate has a direct influence on the dewetting dynamic. In addition, we demonstrate
that residual stresses, which can be stored in the films due to their viscoelasticity, are a source of destabilization for
polymer films, and accelerate the dewetting process. 相似文献
4.
The Dewetting of thin polymer films (60–300 nm) on a
non-wettable liquid substrate has been studied in the vicinity of
their glass transition temperature. In our experiment, we observe a global
contraction of the film while its thickness remains uniform. We
show that, in this case, the strain corresponds to simple extension, and we verify that it is linear with the stress applied
by
the surface tension. This allows direct measurement of the
stress/strain response as a function of time, and thus permits the
measurement of an effective compliance of the thin films. It is,
however, difficult to obtain a complete viscoelastic
characterization, as the short time response is highly dependant on
the physical age of the sample. Experimental results underline the
effects of residual stress and friction when dewetting is analyzed
on rigid substrates. 相似文献
5.
We develop a renormalization group approach for cyclizing polymers for the case when chain ends are initially close together
(ring initial conditions). We analyze the behavior at times much shorter than the longest polymer relaxation time. In agreement
with our previous work (Europhys. Lett.
73, 621 (2006)) we find that the leading time dependence of the reaction rate k(t) for ring initial conditions and equilibrium initial conditions are related, namely k
ring(t) ∝ t
-δ and k
eq(t) ∝ t
1-δ for times less than the longest polymer relaxation time. Here δ is an effective exponent which approaches δ = 5/4 for very
long Rouse chains. Our present analysis also suggests a “sub-leading” term proportional to (ln t)/t which should be particularly significant for smaller values of the renormalized reaction rate and early times. For Zimm dynamics,
our RG analysis indicates that the leading time dependence for the reaction rate is k(t) ∼ 1/t for very long chains. The leading term is again consistent with the expected relation between ring and equilibrium initial
conditions. We also find a logarithmic correction term which we “exponentiate” to a logarithmic form with a Landau pole. The
presence of the logarithm is particularly important for smaller chains and, in the Zimm case, large values of the reaction
rate. 相似文献
6.
It is shown that orientational ordering of anisotropic organic
molecules with permanent magnetic dipoles in a tilted film should
result in a macroscopic magnetisation in the plane of the film. The
important requirement here is that the molecules are strongly
biaxial, and the corresponding biaxial orientational order parameter
in the tilted phase is sufficiently large. The molecules should also
be characterised by a reduced symmetry of the magnetic core compared
with existing “single molecular magnets". Possible symmetry groups of the
molecular magnetic core, which allow for the existence of nonzero
average magnetic moment, are discussed in detail. The tilt-induced
ferromagnetic ordering of such molecules may be determined by
nonmagnetic intermolecular interactions including, for example,
quadrupole-quadrupole electrostatic interaction or dispersion
interaction between molecules of particular symmetry. Magnetic
intermolecular interactions are not important here, and as a result
the induced ferromagnetic state may be stable in any temperature
range where the corresponding tilted film is stable. These general
conclusions, which form a theoretical foundation for the existence
of novel fluid low-dimensional magnetic materials, are based on
symmetry arguments and are supported by a simple mean-field
molecular model. We also discuss how such induced ferromagnetic
ordering may be observed in Langmuir-Blodgett films which seem to be
the best candidates for preparing these magnetic materials. 相似文献
7.
N. Rehse C. Wang M. Hund M. Geoghegan R. Magerle G. Krausch 《The European physical journal. E, Soft matter》2001,4(1):69-76
We study the wetting behaviour of thin polystyrene (PS) films on regularly corrugated silicon substrates. Below a critical
film thickness the PS films are unstable and dewet the substrates. The dewetting process leads to the formation of nanoscopic
PS channels filling the grooves of the corrugated substrates. Films thicker than the critical thickness appear stable and
follow the underlying corrugation pattern. The critical thickness is found to scale with the radius of gyration of the unperturbed
polymer chains.
Received 6 April 2000 and Received in final form 24 August 2000 相似文献
8.
Tomar G Shankar V Shukla SK Sharma A Biswas G 《The European physical journal. E, Soft matter》2006,20(2):185-200
The instability, rupture, and subsequent growth of holes in a thin Jeffreys-type viscoelastic film under the influence of
long-range van der Waals force are investigated using both linear stability analysis and nonlinear numerical solutions. The
linear stability analysis of full governing equations valid for arbitrary wave numbers shows that although fluid rheology
does not influence the dominant length scale of the instability, it significantly affects the growth rate. It is shown that
neglect of inertia and solvent dynamics results in a nonphysical singularity in the growth rate beyond a critical value of
relaxation time. We further carry out numerical simulations of a set of long-wave, nonlinear differential equations (also
derived in Rauscher et al., Eur. Phys. J. E 17, 373 (2005)) governing the evolution of the free surface. The nonlinear simulations, in their domain of validity, confirm
the results of the linear analysis. Interestingly, results from nonlinear simulations further show that both for Newtonian
and viscoelastic liquids, the shape and the dewetting dynamics of a hole are identical when examined in terms of a rescaled
time which depends on rheological parameters. Thus, viscoelasticity of Jeffreys type merely accelerates the growth rate, without
however affecting the important morphological characteristics. 相似文献
9.
Kujawa P Watanabe H Tanaka F Winnik FM 《The European physical journal. E, Soft matter》2005,17(2):129-137
We report the first study of aqueous solutions (0.025 gL-1 to 46 gL-1) of a telechelic poly(N-isopropylacrylamide) with octadecyl termini (C18-PNIPAM-C18, Mw: 37000, 320 NIPAM units, Mw/ Mn = 1.07) obtained by reversible addition-fragmentation chain transfer (RAFT) free radical polymerization of N-isopropylacrylamide. Static and dynamic light scattering measurements and fluorescence spectroscopy, using 8-anilino-1-naphthalenesulfonic acid (ANS) as probe, yielded the concentration dependence of the size and aggregation number of C18-PNIPAM-C18 micelles in cold ( 20°C) dilute aqueous solutions. Concentrated solutions ( c > 20gL-1) form transient gels exhibiting an oscillatory shear behavior that can be approximated by a single-relaxation Maxwellian model. Aqueous solutions of C18-PNIPAM-C18 undergo a phase transition upon heating to 31.5°C as determined by microcalorimetry. The heat-induced phase separation of dilute (0.025 gL-1) C18-PNIPAM-C18 solutions yields a fluid that is colloidally stable at temperatures higher than 33°C. The overall results are consistent with a model assuming the formation of flowerlike micelles in the dilute regime and a network of micelles connected by telechelic chains in the concentrated regime. 相似文献
10.
Ultra thin films of glassy polymers such as polystyrene (PS) can show a) anomalously large thickness changes, b) unexpected
dewetting properties, c) large shifts in the glass temperature Tg. The present discussion focusses mainly on point a). A certain cascade of metastable states is presented together with (tentative)
explanations.
Received 1 March 2001 and Received in final form 10 May 2001 相似文献
11.
Massa MV Dalnoki-Veress K Forrest JA 《The European physical journal. E, Soft matter》2003,11(2):191-198
We present a detailed study of the kinetics of
crystallization for thin films of poly(ethylene oxide) (PEO).
Measurements of the growth rate have been carried out using
optical-microscopy techniques on films of monodisperse PEO.
Films with thicknesses from 13 nm to ~2 m were crystallized
isothermally at temperatures ~20°C below the melting point. A
remarkable non-monotonic
slowing-down of the crystal growth is observed for films with
thickness less than ~400 nm. The changes in the growth rate from
bulk-like values is significant and corresponds to a factor of
40 decrease for the thinnest films studied. The morphologies of
isothermally crystallized samples are studied using atomic-force
microscopy. We find that a morphology, similar to
diffusion-controlled growth (dendritic growth and densely
branched growth), is observed for films with
h < 150 nm. In addition,
changes in the morphology occur for thicknesses consistent with
changes in the growth rate as a function of film thickness. 相似文献
12.
K. Narumi Y. Xu K. Miyashita H. Naramoto 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):385-388
We report a new effect of ion irradiation on
C60 thin films:
C60 thin films irradiated with 7-MeV
C2+ ions show resistance to
photopolymerization. The resistance increases with increasing
ion fluence of irradiation. The effect is qualitatively
explained by the fact that the number of a
C60 pair satisfying the topochemical
requirement for photochemical reaction in solids decreases by
destruction of C60 molecules accompanied
by lattice disorder. 相似文献
13.
Sharp JS Vader D Forrest JA Smith MI Khomenko M Dalnoki-Veress K 《The European physical journal. E, Soft matter》2006,19(4):423-432
Optical microscopy and atomic force microscopy were used to study a novel roughness-induced wrinkling instability in thin-film
bilayers of poly(ethylene oxide) (PEO) and polystyrene (PS). The observed wrinkling morphology is manifested as a periodic
undulation at the surface of the samples and occurs when the bilayers are heated above the melting temperature of the semi
crystalline PEO (Tm = 63
) layer. During the wrinkling of the glassy PS capping layers the system selects a characteristic wavelength that has the
largest amplitude growth rate. This initial wavelength is shown to increase monotonically with increasing thickness of the
PEO layer. We also show that for a given PEO film thickness, the wavelength can be varied independently by changing the thickness
of the PS capping layers. A model based upon a simple linear stability analysis was developed to analyse the data collected
for the PS and PEO film thickness dependences of the fastest growing wavelength in the system. The predictions of this theory
are that the strain induced in the PS layer caused by changes in the area of the PEO/PS interface during the melting of the
PEO are sufficient to drive the wrinkling instability. A consideration of the mechanical response of the PEO and PS layers
to the deformations caused by wrinkling then allows us to use this simple theory to predict the fastest growing wavelength
in the system. 相似文献
14.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
15.
B. Gompf D. Faltermeier C. Redling M. Dressel J. Pflaum 《The European physical journal. E, Soft matter》2008,27(4):421-424
X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry were used to study tetracene thin films as a function
of deposition rate. A comparative analysis of the thickness and roughness values allows for detailed modelling of the film
morphology. An interdigitated growth mode is established for the coexisting thin film and bulk phases. By comparison with
the respective quinone-derivative of tetracene, we were additionally able to identify reaction products by their optical response. 相似文献
16.
Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous.
The characteristic size of these heterogeneities has been measured to be a few nanometers at T
g. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length
scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows
then to interpret quantitatively small probes diffusion experiments.
Received 29 March 2002 and Received in final form 11 November 2002
RID="a"
ID="a"e-mail: long@lps.u-psud.fr 相似文献
17.
P. Le Fèvre H. Magnan D. Chandesris 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):555-562
The crystallographic structure of thin Ni films deposited on Cu(001) has been studied using Surface Extended X-ray Absorption
Fine Structure (SEXAFS). Taking advantage of the linear polarization of the synchrotron radiation, we have shown that Ni adopts
the Cu lattice parameter parallel to the interface. This lateral expansion induces a longitudinal compression of the unit
cell, leading to a face centered tetragonal structure of the Ni films from 3 to 10 monolayers. The temperature dependence
of the EXAFS oscillations has allowed to measure strain inside the Ni layers.
Received 22 December 1998 相似文献
18.
The compositional relaxation in random copolymer systems on a macroscopic scale is considered in theory. A set of diffusion
equations is derived that describes the motion of chains of different composition and then converted into coupled equations
for statistical moments of the compositional distribution. Several ways to solve the closure problem for these equations are
discussed. The simplest is the situation when the shape of the transient compositional distribution can be predicted a priori, for example, a bimodal distribution is kept during interdiffusion of two copolymers that are not very close in composition.
For a general case, it is shown that the cumulant-neglect closure based on the truncation of high-order cumulants is an effective
method to get an approximate solution in terms of the time-dependent local mean composition and its dispersion. This method
is applied to non-homogeneous compatible polymer systems, such as a random copolymer AB of a composition varying in space,
a bilayer of Bernoullian copolymers AB of different composition, and a bilayer of homopolymers A and B, in which an autocatalytic
polymer-analogous reaction A → B takes place, with possibility of the neighbor group effect. It is found that the interdiffusion
can lead to a substantial broadening of the local compositional distribution, which, in turn, accelerates the system dynamics
and promotes chemical reactions. 相似文献
19.
Equilibrium phase coexistence between two chemical species implies the equality of the chemical potentials and of the osmotic
pressures. We study this problem on a deformable membrane when one type of the molecules serves as anchor for polymeric chains
immersed in the surrounding medium (considered as a good solvent). We derive the general conditions for phase coexistence
when both the curvature of the membrane and the density field of the anchor molecule are free to adjust themselves. We show
that curvature favors phase segregation. Our model predicts that membranes decorated with polymeric chains exhibit new shape
bifurcations without equivalent in fixed density systems.
Received: 26 November 2002 / Accepted: 2 April 2003 / Published online: 12 May 2003
RID="a"
ID="a"e-mail: nicolas@drfmc.ceng.cea.fr
RID="b"
ID="b"e-mail: bfourcade@cea.fr 相似文献
20.
Glass transition for atactic poly(methyl methacrylate)
(a-PMMA) prepared in
nano-cells by microemulsion polymerization was measured at a
faster heating rate after slow cooling of the sample from a
temperature above Tg. An
additional enthalpy relaxation and glass transition were
observed at higher temperatures for the a-PMMA sample due to the partial
organization of the chain segments which occurred during
microemulsion polymerization. The re-precipitated
a-PMMA did not show any
self-organization under the same thermal conditions, although
there are no changes in molecular weight or tacticity of the
polymer chains. A depletion-interaction phenomenon was
understood to provide entropic force for the self-organization
of polymer chains inside the walls of the microemulsion cells. 相似文献