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1.
Godinho MH Trindade AC Figueirinhas JL Melo LV Brogueira P Deus AM Teixeira PI 《The European physical journal. E, Soft matter》2006,21(4):319-330
We have studied the control and manipulation of tuneable equilibrium structures in a free-standing urethane/urea elastomer
film by means of atomic force microscopy, small-angle light scattering and polarising optical microscopy. The urethane/urea
elastomer was prepared by reacting a poly(propyleneoxide)-based triisocyanate-terminated prepolymer (PU) with poly(butadienediol)
(PBDO), with a weight ratio of 60% PU/40% PBDO. An elastomer film was shear-cast onto a glass plate and allowed to cure, first
in an oven, then in air. Latent micro- and nano-periodic patterns are induced by ultra-violet (UV) irradiation of the film
and can be “developed” by applying a plane uniaxial stress or by immersing the elastomer in an appropriate solvent and then
drying it. For this elastomer we describe six pattern states, how they are related and how they can be manipulated. The morphological
features of the UV-exposed film surface can be tuned, reproducibly and reversibly, by switching the direction of the applied
mechanical field. Elastomers extracted in toluene exhibit different surface patterns depending upon the state in which they
were developed. Stress-strain data collected for the films before and after UV irradiation reveal anisotropy induced by the
shear-casting conditions and enhanced by the mechanical field. We have interpreted our results by assuming the film to consist
of a thin, stiff surface layer (“skin”) lying atop a thicker, softer substrate (“bulk”). The skin's higher stiffness is hypothesised
to be due to the more extensive cross-linking of chains located near the surface by the UV radiation. Patterns would thus
arise as a competition between the effects of bending the skin and stretching/compressing the bulk, as in the work of Cerda
and Mahadevan (Phys. Rev. Lett. 90, 074302 (2003)). We present some preliminary results of a simulation of this model using the Finite Element package ABAQUS. 相似文献
2.
Chécot F Lecommandoux S Klok HA Gnanou Y 《The European physical journal. E, Soft matter》2003,10(1):25-35
This paper discusses the self-assembly of block copolymers into vesicular morphology. After a brief state of art of the field,
a system based on an amphiphilic poly(butadiene)-b-poly(-L-glutamic acid) (PB-b-PGA) diblock copolymer in aqueous solution is discussed in detail. The aggregation behavior of this block copolymer has been
investigated by means of fluorescence spectroscopy, dynamic (DLS) and static (SLS) light scattering as well as transmission
electron microscopy (TEM). The diblock copolymer was found to form well-defined vesicles in water. The size of these so-called
polymersomes or peptosomes could be reversibly manipulated as a function of both pH and ion strength. Depending on the pH
of the aqueous solution, the hydrodynamic radii of these vesicles were found to vary from 100 nm to 150 nm. By cross-linking
the 1,2-vinyl double bonds present in the polybutadiene block, the ability to transform a transient supramolecular self-organized
aggregate into a permanent “shape-persistent stimuli-responsive nanoparticle” has been demonstrated.
Received 25 June 2002 and Received in final form 22 October 2002 Published online: 11 March 2003 相似文献
3.
B. Lotz 《The European physical journal. E, Soft matter》2000,3(2):185-194
Contrary to most or all other materials, crystallization of chiral but racemic polymers such as isotactic polypropylene is
accompanied by a conformational rearrangement which leads to helical geometries: the building units of the crystal are helical
stems, -20nm long, which can be either right-handed or left-handed. Helical hand cannot be reversed within the crystal structure: it is therefore a permanent marker and an indicator of molecular processes (in particular segregation/selection of helical hands) which take place during crystal
growth, and more precisely during the crucial step of “efficient” helical stem deposition. The issue of proper helical hand
selection during polymer crystal growth is mainly illustrated with isotactic polypropylene. Its various crystalline polymorphs
(, , and smectic) display virtually all possible combinations of helical hands, azimuthal settings and even non-parallel orientation
of helix axes in space. Furthermore, a specific homoepitaxy which generates a lamellar branching in the phase “quadrites” and composite structures makes it possible a) to determine the helical hand and associated azimuthal setting of every stem in
the crystalline entities and b) to determine the impact on the crystal structure and morphology of “mistakes” in helical hand
of the depositing stem. Analysis of these morphologies demonstrates that the crystallization of isotactic polypropylene (and
by implication of other achiral, helical polymers) is a highly sequential and “substrate-determined” process, i.e. that the depositing stem probes the topography of the growth face prior to attachment. These observations appear difficult to reconcile with crystallization schemes in which molecules (helical segments) are
prearranged in a kind of pseudo-crystalline bundle (and as such, are not subjected to the high constraints of crystal symmetry)
before deposition as a preassembled entity on the substrate.
Received: 5 May 2000 相似文献
4.
A. I. Belousova Yu. E. Lozovikb 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):251-264
A two dimensional (2D) classical system of dipole particles confined by a quadratic potential is studied. This system can
be used as a model for rare electrons in semiconductor structures near a metal electrode, indirect excitons in coupled quantum
dots etc. For clusters of N ≤ 80 particles ground state configurations and appropriate eigenfrequencies and eigenvectors for the normal modes are found.
Monte-Carlo and molecular dynamic methods are used to study the order-disorder transition (the “melting” of clusters). In
mesoscopic clusters (N < 37) there is a hierarchy of transitions: at lower temperatures an intershell orientational disordering of pairs of shells
takes place; at higher temperatures the intershell diffusion sets in and the shell structure disappears. In “macroscopic”
clusters (N > 37) an orientational “melting” of only the outer shell is possible. The most stable clusters (having both maximal lowest
nonzero eigenfrequencies and maximal temperatures of total melting) are those of completed crystal shells which are concentric
groups of nodes of 2D hexagonal lattice with a number of nodes placed in the center of them. The picture of disordering in
clusters is compared with that in an infinite 2D dipole system. The study of the radial diffusion constant, the structure
factor, the local minima distribution and other quantities shows that the melting temperature is a nonmonotonic function of
the number of particles in the system. The dynamical equilibrium between “solid-like” and “orientationally disordered” forms
of clusters is considered. 相似文献
5.
D. Reinelt P. Boltenhagen N. Rivier 《The European physical journal. E, Soft matter》2001,4(3):299-304
The “staircase” (2,1,1) foam structure in an ordered foam under expansion in a cylindrical tube and the structural transition
to the “bamboo” (1,1,0) structure are studied experimentally, analytically, and numerically using the Surface Evolver minimization
program. An analytical expression of the oblique interface in the (2,1,1) structure, a minimal surface, but curved by stretching
of the foam, is given as a classic example of singular perturbation (boundary layer) theory. The structural transition from
staircase structure to bamboo structure takes place at a considerable dilation. The transition is not due to an edge length
tending to zero continuously with dilation, but results from the equilibrium (2,1,1) solution losing its stability due to
a saddle node bifurcation.
Received 3 August 2000 相似文献
6.
The substrate is shown to induce substantial ordering in diblock copolymer thin films above the bulk order-disorder transition
(ODT) where, thermodynamically, a phase mixed state is favored. Initially, uniform films reorganize to form a hierarchy of
transient surface patterns and stable film thicknesses that depend on the initial film thickness and on the substrate. Self-consistent
field calculations of the free energy of the system for different situations, depending on the relative tendency for the different
block components to be attracted to the substrate and/or free surface, provide an explanation of the formation of the stable
film thicknesses. A continuum picture proposed earlier by Brochard et al.rovides an explanation of the wetting characteristics of this system. In some cases the ordering destabilizes the film so
that dewetting occurs (wetting autophobicity), whereas in other cases the surface ordering results in a kinetic stabilization
of a film that would otherwise dewet.
Received 3 August 2001 and Received in final form 1 November 2001 相似文献
7.
Shusharina NP Alexandridis P Linse P Balijepalli S Gruenbauer HJ 《The European physical journal. E, Soft matter》2003,10(1):45-54
A mean-field lattice theory is applied to predict the self-assembly into ordered structures of an ABC triblock copolymer in
selective solvent. More specifically, the composition-temperature phase diagram has been constructed for the system (C)14(PO)12(EO)17/water, where C stands for methylene, PO for propylene oxide and EO for ethylene oxide. The model predicts thermotropic phase
transitions between the ordered hexagonal, lamellar, reverse hexagonal, and reverse cubic phases, as well as the disordered
phase. The thermotropic behavior is a result of the temperature dependence of water interaction with EO- and PO-segments.
The lyotropic effect (caused by changing the solvent concentration) on the formation of different structures has been found
weak. The structure in the ordered phases is described by analyzing the species volume fraction profiles and the end segment
and junction distributions. A “triple-layer” structure has been found for each of the ordered phases, with each layer rich
in C-, PO-, and EO-segments, respectively. The blocks forming the layers are not stretched. The dependence of the domain spacing
on polymer volume fraction and temperature is also considered.
Received 17 April 2002 Published online: 21 January 2003 相似文献
8.
A. Karanikolas P. Tsolakis G. Bokias C. Tsitsilianis 《The European physical journal. E, Soft matter》2008,27(3):335-343
The self-organization of the double hydrophilic triblock copolymer poly(ethylene oxide)-b-poly(2-vinylpyridine)-b-poly(ethylene
oxide), PEO-b-P2VP-b-PEO, was investigated in dilute aqueous solution under several experimental conditions using turbidimetry,
as well as static and dynamic light scattering. As a result of the temperature-sensitive properties of the end PEO blocks
and the p H-responsive properties of the middle P2VP block, the formation of large star-like micellar nanostructures is observed at
high p H, while at low p H, but in the presence of salt and at high temperature, flower-like micelles are formed. Moreover, the viscosimetric and
dynamic light scattering studies at low p H revealed that micelle-like nanostructures are formed upon mixing the triblock copolymer with poly(acrylic acid), PAA, due
to hydrogen bonding interpolymer complexation. 相似文献
9.
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
10.
Eugen Paal 《Czechoslovak Journal of Physics》2002,52(11):1277-1282
The deformation equation and its integrability condition (Bianchi identity) of a non-(co)associative deformation in operad
algebra are found. Based on physical analogies, two ideas ofcogravity equations are proposed.
Presented at the 11th Colloquium “Quantum Groups and Integrable Systems”, Prague, 20–22 June 2002. 相似文献
11.
Growth kinetics of polymer crystals in bulk 总被引:1,自引:0,他引:1
Temperature-dependent measurements of spherulite growth rates carried out for i-polystyrene, poly(ε -caprolactone) and linear
polyethylene show that the controlling activation barrier diverges at a temperature which is 14K, 22K and 12K, respectively,
below the equilibrium melting points. We discuss the existence of such a “zero growth temperature” T
zg in the framework of a recently introduced thermodynamic multiphase scheme and identify T
zg with the temperature of a (hidden) transition between the melt and a mesomorphic phase which mediates the crystal growth.
The rate-determining step in our model of crystal growth is the attachment of chain sequences from the melt onto the lateral
face of a mesomorphic layer at the growth front. The necessary straightening of the sequence prior to an attachment is the
cause of the activation barrier. A theory based on this view describes correctly the observations. With a knowledge of T
zg it is possible to fully establish the nanophase diagram describing the stability ranges of crystalline and mesomorphic layers
in a melt. An evaluation of data from small-angle X-ray scattering, calorimetry and optical growth rate measurements yields
heats of transition and surface free energies of crystals and mesophase layers, as well as the activation barrier per monomer
associated with the chain stretching. According to the theory, the temperature dependence of the crystallization rate is determined
by both the activation energy per monomer and the surface free energy of the preceding mesomorphic layer. Data indicate that
the easiness of crystallization in polyethylene is first of all due to a particularly low surface free energy of the mesomorphic
layer. 相似文献
12.
Sharp, Teichroeb and Forrest [J.S. Sharp, J.H. Teichroeb, J.A.
Forrest, Eur. Phys. J. E 15, 473 (2004)] recently published a viscoelastic
contact mechanics analysis of the embedment of gold nanospheres into a
polystyrene (PS) surface. In the present comment, we investigate the
viscoelastic response of the surface and conclude that the embedment
experiments do not support the hypothesis of a liquid surface layer of
sufficiently reduced “rheological temperature” to explain reports of very
large reductions in the glass temperature of freely standing ultrathin
polystyrene films. We also report some errors and discrepancies in the paper
under comment that resulted in an inability to reproduce the reported
calculations. We present our findings of error in a spirit of clarifying the
problem of embedment of spheres into surfaces and in order that others can
understand why they may not reproduce the results reported by Sharp,
Teichroeb and Forrest. In the comment, we also examine the effects of the
magnitude of the forces that result from the polymer surface-nanosphere
particle interactions on the viscoelastic properties deduced from the
embedment data and we provide a comparison of apparent surface or
“rheological” temperature vs. experimental temperature that indicates
further work needs to be performed to fully understand the surface embedment
experiments. Finally, we comment that the nanosphere embedment measurements
have potential as a powerful tool to determine surface viscoelastic
properties. 相似文献
13.
C.M. Papadakis K. Almdal K. Mortensen F. Rittig G. Fleischer P. Štěpánek 《The European physical journal. E, Soft matter》2000,1(4):275-283
We have studied the bulk dynamics of a compositionally asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS)
diblock copolymer in a large temperature range both in the ordered and in the disordered state. The volume fraction of the
PEP block is 0.22. Apart from the disordered state, the sample shows three ordered morphologies. Using dynamic light scattering,
we have investigated the dynamics in all four phases and combined these results with those obtained using pulsed field gradient
NMR. In the disordered state, we find--apart from the slow cluster mode--the heterogeneity mode related to the self-diffusion
of single chains. The relaxation time of this mode, reduced by temperature and the zero-shear viscosity , , increases with temperature. In the cubic phase right below the ODT temperature, we observe two diffusive processes, and
we attribute the faster one to the mutual diffusion of micelles and block copolymers not bound to micelles (“free chains”)
through the PDMS matrix. The slower mode may either be due to the mutual diffusion of free chains and chains bound to PEP
micelles or to the cooperative diffusion of micellar aggregates. In the non-cubic ordered state at intermediate temperatures,
an additional weak diffusive mode is observed. The low-temperature ordered state is body-centered cubic, and here, only the
mutual diffusion of micelles and free chains lies in our experimental time window.
Received 19 March 1999 and Received in final form 25 August 1999 相似文献
14.
A. Aradian E. Raphaël P.G. de Gennes 《The European physical journal. E, Soft matter》2000,2(4):367-376
We consider a porous solid covered with a water film (or with a drop) in situations where the liquid is pumped in, either
spontaneously (if the porous medium is hydrophilic) or mechanically (by an external pump). The dynamics of dewetting is then
strongly modified. We analyse a few major examples, a) horizontal films, which break at a certain critical thickness, b) the
“modified Landau-Levich problem” where a porous plate moves up from a bath and carries a film: aspiration towards the plate
limits the height H reached by the film, c) certain situation where the hysteresis of contact angles is important.
Received 5 October 1999 and Received in final form 7 February 2000 相似文献
15.
M. Ozer L. J. Graham 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):499-503
In a Hodgkin-Huxley neuron model driven just above threshold, external noise can increase both jitter and latency of the first
spike, an effect called “noise delayed decay” (NDD). This phenomenon is important when considering how neuronal information
is represented, thus by the precise timing of spikes or by their rate. We examine how NDD can be affected by network activity
by varying the model's membrane time constant, τm. We show that NDD is significant for small τm or high network activity, and decreases for large τm, or low network activity. Our results suggest that for inputs just above threshold, the activity of the network constrains
the neuronal coding strategy due to, at least in part, the NDD effect. 相似文献
16.
“Polymersomes” are vesicular structures made from the self-assembly of block copolymers. Such structures present outstanding
interest for different applications such as micro- or nano-reactor, drug release or can simply be used as tool for understanding
basic biological mechanisms. The use of polymersomes in such applications is strongly related to the way their membrane properties
are controlled and tuned either by a precise molecular design of the constituting block or by addition of specific components
inside the membrane (formulation approaches). Typical membrane properties of polymersomes obtained from the self-assembly
of “coil coil” block copolymer since the end of the nineties will be first briefly reviewed and compared to those of their
lipidic analogues, named liposomes. Therefore the different approaches able to modulate their permeability, mechanical properties
or ability to release loaded drugs, using macromolecular engineering or formulations, are detailed. To conclude, the most
recent advances to modulate the polymersomes’ properties and systems that appear very promising especially for biomedical
application or for the development of complex and bio-mimetic structures are presented. 相似文献
17.
We found an exact expression for the Flory radius R
F of Gaussian polymers placed in an external periodic field. This solution is expressed in terms of the two parameters η and
a that describe the reduced strength of an external field and the period of the field to the polymer gyration radius ratio,
respectively. R
F is found to be a decaying function of η for any values of a . Provided that the gyration radius is of the order of the period of an external field or less, the ground-state (GS) approximation
of the exact result for R
F is shown to give qualitatively incorrect results. In addition to the “ground-state” contribution, the exact solution for
R
F contains an additional term that is overlooked by the GS approximation. This term gives rise to the fact that R
F as a function of η exhibits power law behavior (rather than exponential decay obtained from the GS result) once η exceeds
the threshold value ηcon . 相似文献
18.
L.D. ZhangW.L. Liu C.L. XiaoJ.S. Yao Z.P. FanX.L. Sun X. ZhangL. Wang X.Q. Wang 《Journal of magnetism and magnetic materials》2011,323(23):3087-3091
The use of a block copolymer, poly (styrene)-b-poly (acrylic acid) (PS-b-PAA) to prepare a magnetic nanocomposite was investigated. Poly (styrene)-poly (t-butyl acrylate) block copolymer, being synthesized by atom transfer radical polymerization, was hydrolyzed with hydrochloric acid for obtaining PS-b-PAA. The obtained PS-b-PAA was then compounded with the modified γ-Fe2O3, and subsequently the magnetic nanocomposite was achieved. The products were characterized by 1H NMR, FTIR, gel permeation chromatography, thermogravimetric analysis, transmission electron microscopy and vibrating sample magnetometer. The results showed that the nanocomposites exhibited soft magnetism, with the mean diameter of 100 nm approximately. 相似文献
19.
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