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1.
J. L. Viota J. D. G. Durán A. V. Delgado 《The European physical journal. E, Soft matter》2009,29(1):87-94
In this paper we describe the magnetorheological behavior of aqueous suspensions consisting of magnetite particles of two
size populations, in the micrometer and nanometer scale, respectively. Previous works on the magnetorheology of oil-based
fluids demonstrated that the addition of nanoparticles has a very significant effect on the intensity of the magnetorheological
effect. The present contribution confirms such results in the case of aqueous fluids, based on the dependence of the yield
stress and the viscosity of the bimodal suspensions on both the composition of the mixtures and the magnetic field strength.
It is demonstrated that for a given concentration of micrometer particles, increasing the amount of nanometer magnetite provokes
a clear enhancement in the yield stress for all the magnetic fields applied. This is proposed to be due to the formation of
heterogeneous aggregates that improve the stability of the suspensions and ease the building of well-arranged field-induced
structures. The behavior of both the yield stress and the post-yield viscosity agrees better with the predictions of standard
chain models when the relative proportion of both types of particles confers optimum stability to the bimodal dispersions. 相似文献
2.
We describe a physically associating triblock copolymer-based gel that exhibits a reversible transition between solid and liquid states at a temperature of approximately 55°C. The thermal transition of the gel enables us to compare the properties of liquid suspensions and elastic composites with identical particle loadings, with particle volume fractions as large as 0.55. The suspension viscosity and the composite elasticity scale in a similar manner with the overall particle volume fraction, a result that is rationalized in terms of an effective strain amplification factor that depends only on the particle loading. Measured values of the strain amplification factor are in good agreement with the expected form for well-dispersed spheres. We also find that the elastic composites are exceptionally strong, with fracture strengths that exceed the modulus of the base gel by a factor of 100 or more. Deviations from purely elastic behavior became important for high particle volume fractions, and were probed by stress relaxation experiments. 相似文献
3.
It is well known that the morphology of block copolymer aggregates depends on polymer properties such as the molecular weight,
the relative block length, and the chemical nature of the repeat unit. Recently, we have shown that if aggregates are allowed
to self-assemble in solution, then in addition to the above factors, a high degree of control over the aggregate architecture
can be achieved by adjusting the solution conditions. Factors such as the water content in the solvent mixture, the solvent
nature and composition, the presence of additives (ions, surfactants, and homopolymer) and the polymer concentration were
successfully employed to control the aggregate shape and size. In this paper, we review a series of studies performed in our
group to show how solution properties can control the architecture of aggregates prepared from a given copolymer. The control
mechanism is explained in terms of the effect of each property on the forces that govern the formation of any given morphology,
namely the core-chain stretching, corona-chain repulsion and interfacial tension.
Received 30 April 2002 and Received in final form 3 September 2002 Published online: 21 January 2003 相似文献
4.
M. Meyer Yu. L. Raikher O. Sandre A. Bée V. Cabuil V. Dupuis P. Licinio R. Perzynski 《The European physical journal. E, Soft matter》2008,26(4):355-360
Magnetic and orientational behavior of nickel hydroxide nanoplatelets ionically stabilized in a liquid matrix is studied.
Under an applied field the platelets orient their faces normal to its direction. For characterization of the individual behavior
of dispersed and non-interacting particles three techniques are used: SAXS, SQUID and magneto-optics. Analysis reveals that
nickel hydroxide in a platelet phase is paramagnetic with a pronounced anisotropy of the intrinsic susceptibility, the major
component of which (in the direction normal to platelet face) exceeds the minor one by about 25%. 相似文献
5.
Núñez A Darias R Pinto R Paredes V R Medina E 《The European physical journal. E, Soft matter》2002,9(4):327-334
We study a model of concentrated suspensions under shear in two dimensions. Interactions between suspended particles are dominated
by direct-contact viscoelastic forces and the particles are neutrally bouyant. The bimodal suspensions consist of a variable
proportion between large and small droplets, with a fixed global suspended fraction. Going beyond the assumptions of the classical
theory of Farris (R.J. Farris, Trans. Soc. Rheol. 12, 281 (1968)), we discuss a shear viscosity minimum, as a function of the small-to-large-particle ratio, in shear geometries
imposed by external body forces and boundaries. Within a linear-response scheme, we find the dependence of the viscosity minimum
on the imposed shear and the microscopic drop friction parameters. We also discuss the viscosity minimum under dynamically
imposed shear applied by boundaries. We find a reduction of macroscopic viscosity with the increase of the microscopic friction
parameters that is understood using a simple two-drop model. Our simulation results are qualitatively consistent with recent
experiments in concentrated bimodal emulsions with a highly viscous or rigid suspended component.
Received 28 June 2002
RID="a"
ID="a"e-mail: ernesto@pion.ivic.ve 相似文献
6.
NMR velocimetry has been used to observe the steady-shear rheological behaviour of a concentrated suspension of hard-sphere
like 370 nm diameter PMMA core-shell latex particles at the volume fraction Φ = 0.46, the liquid core of the spheres rendering
possible NMR observation of the particles themselves. Rheological measurements in a cone-and-plate geometry indicate that
when aged (i.e. left at rest for two weeks), the material exhibits yield stress behaviour at very low shear rates. For shear rates greater
than 1 s - 1 a transition to liquid-like behaviour was observed, leading to a rejuvenated fluid state which exhibits shear-thinning behaviour
over a wide range of shear rates. A similar yield stress behaviour was reflected in NMR velocimetry measurements in a Couette
geometry, where the solid-to liquid transition could be clearly observed. Under steady-state flow, the fluid state inside
the radius at which yield stress was observed, exhibited shear-thinning behaviour with a power law exponent n slowly approaching
unity with increasing shear rate. This behaviour has some similarities with a model of Derec et al. in which aging and rejuvenation effects compete. Substantial wall slip was observed both at the inner and at the outer wall,
an effect which disappeared as the shear rate was increased. No radial particle migration from the high-shear region at the
inner wall was observed. 相似文献
7.
Ramachandran S Sunil Kumar PB Pagonabarraga I 《The European physical journal. E, Soft matter》2006,20(2):151-158
We present a Lattice-Boltzmann method for simulating self-propelling (active) colloidal particles in two dimensions. Active
particles with symmetric and asymmetric force distribution on their surface are considered. The velocity field generated by
a single active particle, changing its orientation randomly, and the different time scales involved are characterized in detail.
The steady-state speed distribution in the fluid, resulting from the activity, is shown to deviate considerably from the equilibrium
distribution. 相似文献
8.
The airborne transport of particles on a granular surface by the
saltation mechanism is studied through numerical simulation of
particles dragged by turbulent air flow. We calculate the
saturated flux qs and show that its dependence on the wind
strength u* is consistent with several empirical relations
obtained from experimental measurements. We propose and explain
a new relation for fluxes close to the threshold velocity ut,
namely, qs=a(u*-ut)α with α≈2. We
also obtain the distortion of the velocity profile of the wind due to the
drag of the particles and find a novel dynamical
scaling relation. We also obtain a new expression for the dependence of
the height of the saltation layer as function of the strength of the wind. 相似文献
9.
10.
G. A. Adebayo B. C. Anusionwu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):423-427
Molecular dynamics simulations (MD) of dynamical properties of molten binary
Ag-Cu alloy is presented at various temperature above the eutetic
temperature. Atoms in the system have been modelled through an interatomic
Lennard-Jones potential interaction. The structure, through the effective pair
distribution function allows to determine the Enksog collision frequency as
well as the coordination of atoms in the first shell. The surface traction,
which is the force per unit area between the species shows a long separation
oscillation about the value zero, while the collision frequency of pairs of
atoms increase with increasing temperature. The adhesion energy between
components found to be 3.4178 J/m2. In agreement with theory, we found a
decrease in surface tension of Ag-Cu alloy as temperature increases.
Separation of atoms pairs in the first shell might be responsible for a
non linear relationship found between temperature and coordination number
in present calculations. 相似文献
11.
We use a multispeckle diffusing wave spectroscopy (MSDWS) method to study the ensemble-averaged dynamics of the fluctuating
speckle pattern when illuminating colloidal particles suspended in a static and opaque porous medium with a coherent light
source. Experiments were performed with Brownian latex particles in a random packing of glass spheres. The mixing of the light
scattered by the moving colloidal particles and the porous matrix gives rise to a plateau value of the intensity autocorrelation
function in the long-waiting-time limit. From the plateau in the correlation function, we can determine the fraction of light
scattered from moving particles and estimate the photon mean free path in the colloidal solution. The method opens up promising
possibilities to probe the static fraction in semisolid materials. 相似文献
12.
We report on the rheology of a lyotropic lamellar surfactant solution (SDS/dodecane/pentanol/ water), and identify a discontinuous
transition between two shear thinning regimes which correspond to the low-stress lamellar phase and the more viscous shear-induced
multilamellar vesicle, or “onion” phase. We study in detail the flow curve, stress as a function of shear rate, during the
transition region, and present evidence that the region consists of a shear-banded phase where the material has macroscopically
separated into bands of lamellae and onions stacked in the vorticity direction. We infer very slow and irregular transformations
from lamellae to onions as the stress is increased through the two-phase region, and identify distinct events consistent with
the nucleation of small fractions of onions that coexist with sheared lamellae. 相似文献
13.
Studies performed on strong polyelectrolytes and on a weak polyelectrolyte, sodium poly(acrylate), show that their stability
in presence of multivalent cations depends on the chemical nature of the charged side groups of the polymer. For sulfonate
groups (SO3
-) or sulfate groups (OSO3
-) phase separation generally occurs in presence of inorganic cations of valency 3 (as La3+) or larger and a resolubilization takes place at high salt concentration. The interactions of the polyelectrolyte with multivalent
cations are of electrostatic origin and the phase diagrams are weakly dependent on the chemical nature of the polymer backbone
and on the specificity of the counterions. For acrylate groups, (COO-), the phase separation was observed with inorganic cations of valency 2 (as Ca2+) or larger without resolubilization at high salt concentration. The phase separation is due to a chemical association between
cations and acrylate groups of two neighboring monomers of the same chain. This chemical association creates a hydrophobic
complex by dehydrating both monomer and cation. With organic trivalent cation, as spermidine +H3N(CH2)4NH2
+(CH2)3NH3
+, where no chemical association occurs with the charged side groups COO- or SO3
- of the polyelectrolyte, similar phase diagrams were observed whatever was the polyelectrolyte with a resolubilization at
high trivalent cation concentration.
Received 3 March 1999 and Received in final form 2 September 1999 相似文献
14.
P. Guenoun M. Delsanti D. Gazeau J.W. Mays D.C. Cook M. Tirrell M. Tirrell L. Auvray 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):77-86
Aqueous micellar solutions of ionic/neutral block copolymers have been studied by light scattering, small angle neutron scattering
and small angle X-ray scattering. We made use of a polymer comprised of a short hydrophobic block (polyethylene-propylene)
PEP and of a long polyelectrolytic block (polystyrene-sulfonate) PSSNa which has been shown previously to micellize in water.
The apparent polydispersity of these micelles is studied in detail, showing the existence of a few large aggregates coexisting
with the population of micelles. Solutions of micelles are found to order above some threshold in polymer concentration. The
order is liquid-like, as demonstrated by the evolution with concentration of the peak observed in the structure factor (), and the degree of order is found to be identical over a large range of concentrations (up to 20 wt%). Consistent values
of the aggregation number of the micelles are found by independent methods. The effect of salt addition on the order is found
to be weak.
Received: 19 June 1997 / Received in final form: 4 September 1997 / Accepted: 9 October 1997 相似文献
15.
M.A. Khaleque G.M. Bhuiyan S. Sharmin R.I.M.A. Rashid S.M. Mujibur Rahman 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):319-322
The partial static structure factors, using the Faber-Ziman (FZ) theory, have been calculated for Ag-In alloy. For 20% Ag
at 623 K and 70% Ag at 973 K, the interionic pair potential based on the Bretonnet-Silbert (BS) formalism are calculated and
the hard sphere diameters for the component elements are estimated from the potential profile using the linearised Weeks-Chandler-Andersen
(LWCA) method. The average number densities are calculated on the assumption that the atomic volumes are simply additive.
The calculated structure factors are compared with the experimental values. The partial structure factors for Ag-Ag at 20%
Ag and In-In at 70% Ag appear to be slightly out of phase with the calculated values particularly in large q-region. From the calculations it appears that this discrepancy is related to the process of derivation of the experimental
structure factors from the total one, and the Ag-In alloy can be described by a mixture of hard spheres.
Received 31 October 2001 and Received in final form 10 January 2002 相似文献
16.
C. Faure N. Decoster F. Argoul 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):87-97
The aggregation of 2D colloidal crystals can be performed by applying an AC field to a colloidal dispersion. This technique
is used in this work for assembling multilamellar vesicles in suspension. The dynamics of the aggregation is followed by real-time
recording of the pictures of the microsphere assembly through a phase contrast microscope. The influence of both the frequency
and the amplitude of the alternating field on the dynamical evolution of the concentration of layered particles is discussed
with respect to their size. A phenomenological model of double layer induced trapping of the particles is proposed and an
electroconvective instability of the fluid surrounding the particles is suggested from the observation of the local dynamics
of the particles, in accordance with a very recent argument of Yeh et al. [#!Yeh:97!#].
Received: 4 December 1997 / Revised: 24 March 1998 /
Accepted: 4 May 1998 相似文献
17.
J.A. Cuesta R.P. Sear 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):233-243
The interplay of interactions between micelles, and the aggregation of these micelles into large, highly anisotropic micelles,
is studied. Simple, hard-body, models of rod-like and disc-like micelles are used, which allows us to apply fundamental measure
theory to determine the free energy. Then we study the phase transition from the fluid phase to a liquid crystalline phase.
We find that aggregation induces a strongly first order transition from a fluid phase of small micelles to a close packed
liquid crystalline phase of infinitely large micelles.
Received: 3 December 1997 相似文献
18.
Kosonen H Valkama S Ruokolainen J Torkkeli M Serimaa R ten Brinke G Ikkala O 《The European physical journal. E, Soft matter》2003,10(1):69-75
We demonstrate that complexation of dodecylbenzenesulphonic acid, DBSA, to a diblock copolymer of polystyrene- block-poly(4-vinylpyridine), PS- block-P4VP, leads to polymeric supramolecules PS- block-P4VP(DBSA)y (y = 1.0, 1.5, and 2.0), which self-organize with a particularly large lamellar periodicity in excess of 1000 A. The structures consist of alternating PS and P4VP(DBSA)y layers, where the latter contains smaller internal structure, probably lamellar. The DBSA side chains are bonded to the pyridines by protonation and hydrogen bonding and they effectively plasticize the material. In this way relatively well-developed structures are obtained even without annealing or macroscopic alignment. Transmission and reflectance measurements show that a relatively narrow and incomplete bandgap exists for supramolecules of high molecular weight block copolymer at ca. 460 nm. 相似文献
19.
T. Klotz S. Schubert K.H. Hoffmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):313-317
The correlations between the segments of a semidilute polymer solution are found to induce correlations in the positions of
small particles added to the solution. Small means a diameter much less than the polymer's correlation length. In the presence
of polymer the particles behave as if they attracted each other. It is shown how the polymer's correlation length may be determined
from a scattering experiment performed on the spheres.
Received: 7 July 1997 / Received in final form: 12 November 1997 / Accepted: 19 November 1997 相似文献
20.
Grohens Y Hamon L Reiter G Soldera A Holl Y 《The European physical journal. E, Soft matter》2002,8(2):217-224
We have measured, the thickness dependence of the glass transition temperature T(g)( h), using ellipsometry at variable temperature, for poly(methyl-methacrylate) (PMMA) of various tacticity in confined geometry. We report that several factors significantly affect T(g)( h): i) polymer microstructure (stereoregularity of PMMA) related to local dynamics; ii) interfacial interactions; iii) conformation of the polymer chains. These results raise many fundamental questions on the origin of the thickness-dependent glass transition. Why and how do the interactions with the substrate significantly affect T(g)( h)? Does T(g)( h) depend on the modifications of conformational parameters of the chains (their entropy)? What is the correlation between local dynamics and T(g)( h) in thin films? The aim of this paper is to summarise these open questions, which should stimulate further investigations in the thin polymer film scientific community. 相似文献