共查询到20条相似文献,搜索用时 15 毫秒
1.
We study the effect of dielectric inhomogeneities on the interaction between two planparallel charged surfaces with oppositely
charged mobile charges in between. The dielectric constant between the surfaces is assumed to be different from the dielectric
constant of the two semiinfinite regions bounded by the surfaces, giving rise to electrostatic image interactions. We show
that on the weak-coupling level the image charge effects are generally small, making their mark only in the second-order fluctuation
term. However, in the strong-coupling limit, the image effects are large and fundamental. They modify the interactions between
the two surfaces in an essential way. Our calculations are particularly useful in the regime of parameters where computer
simulations would be difficult and extremely time consuming due to the complicated nature of the long-range image potentials. 相似文献
2.
Vivarès D Belloni L Tardieu A Bonneté F 《The European physical journal. E, Soft matter》2002,9(1):15-25
We present the experimental and theoretical background of a method to characterize the protein-protein attractive potential
induced by one of the mostly used crystallizing agents in the protein-field, the poly(ethylene glycol) (PEG). This attractive
interaction is commonly called, in colloid physics, the depletion interaction. Small-Angle X-ray Scattering experiments and
numerical treatments based on liquid-state theories were performed on urate oxidase-PEG mixtures with two different PEGs (3350
Da and 8000 Da). A “two-component” approach was used in which the polymer-polymer, the protein-polymer and the protein-protein
pair potentials were determined. The resulting effective protein-protein potential was characterized. This potential is the
sum of the free-polymer protein-protein potential and of the PEG-induced depletion potential. The depletion potential was
found to be hardly dependent upon the protein concentration but strongly function of the polymer size and concentration. Our
results were also compared with two models, which give an analytic expression for the depletion potential.
Received 29 April 2002
RID="a"
ID="a"Present address: CRMC2-CNRS, Campus de Luminy, case 913, F-13288 Marseille Cedex 09, France; e-mail: vivares@crmc2.univ-mrs.fr
RID="b"
ID="b"e-mail: bonnete@crmc2.univ-mrs.fr
RID="c"
ID="c"Laboratory associated to Universities Aix-Marseille II and III. 相似文献
3.
H.-K. Kim E. Tuite B. Nordén B.W. Ninham 《The European physical journal. E, Soft matter》2001,4(4):411-417
The source of the activation energy that allows cutting of DNA by restriction enzymes is unclear. A systematic study of the
cutting efficiency of the type-II restriction endonuclease EcoRI, with varying background electrolyte ion pair and buffer reported here, shows only a modest dependence of efficiency on
cation type. Surprisingly, efficiency does depend strongly on the presumed indifferent anion of the background salt. What
emerges is that competition between the background salt anion and the buffer anion for the enzyme and DNA surfaces is crucial.
The results are unexpected and counterintuitive from the point of view of conventional electrolyte theory. However, taken
together with recent developments in surface chemistry, the results do fall into place and could also suggest a novel mechanism
for enzyme activity as an alternative to metal-activated hydrolysis: microscopic cavitation in a hydrophobic pocket might
be the source of activation energy.
Received 19 June 2000 and Received in final form 17 October 2000 相似文献
4.
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
5.
6.
Bellour M Skouri M Munch JP Hébraud P 《The European physical journal. E, Soft matter》2002,8(4):431-436
We have measured the mean-square displacement of colloidal particles embedded in a semi-dilute solution of worm-like micelles,
using diffusing wave spectroscopy. This allowed us to describe their rheological properties over a very wide time range. At
very short times, the particles diffuse freely in the solvent, and then, they experience the characteristic relaxation times
of the living chains. We deduced directly, from the mean-square displacement of the particles, the mechanical properties of
the micellar solution, not only in the high-frequency regime, but also in the low-frequency range, in which we compared our
results with direct mechanical measurements, and found good agreement.
Received 22 March 2002 and Received in final form 5 June 2002 相似文献
7.
Adhikari R 《The European physical journal. E, Soft matter》2002,9(2):127-134
We calculate the elastic-field-mediated interaction between macroscopic particles in a columnar hexagonal phase. The interaction
is found to be long-ranged and non-central, with both attractive and repulsive parts. We show how the interaction modifies
the particle correlations and the column fluctuations. We also calculate the interaction of particles with the topological
defects of the columnar phase. The particle-defect interaction reduces the mobility of the defects.
Received 14 March 2002 and Received in final form 13 August 2002
RID="a"
ID="a"e-mail: rjoy@physics.iisc.ernet.in 相似文献
8.
The interaction between two parallel plates due to non-adsorbing polymer chains with excluded volume is calculated using the
adsorption method. The adsorption is calculated from the profile of the polymer segment concentration between the plates,
which is obtained from the product function of the concentration profile near a single wall, involving the correlation length.
The renormalization group theory provides expressions for the osmotic pressure and consequently for the osmotic compressibility,
chemical potential and correlation length of a polymer solution. Both the local polymer concentration profiles as well as
the minimum of the interaction potential between the plates agree with recently published self-avoiding random walk computer
simulations.
Received 9 August 2001 相似文献
9.
Castelnovo M Bowles RK Reiss H Gelbart WM 《The European physical journal. E, Soft matter》2003,10(2):191-197
We consider the problem of inserting a stiff chain into a colloidal suspension of particles that interact with it through
excluded volume forces. The free energy of insertion is associated with the work of creating a cavity devoid of colloid and
sufficiently large to accommodate the chain. The corresponding work per unit length is the force that resists the entry of
the chain into the colloidal suspension. In the case of a hard sphere fluid, this work can be calculated straightforwardly
within the scaled particle theory; for solutions of flexible polymers, on the other hand, we employ simple scaling arguments.
The forces computed in these ways are shown, for nanometer chain and colloid diameters, to be of the order of tens of pN for solution volume fractions of a few tenths. These magnitudes are argued to be important for biophysical processes such
as the ejection of DNA from viral capsids into the cell cytoplasm.
Received 18 December 2002 Published online: 16 April 2003
RID="a"
ID="a"e-mail: castel@chem.ucla.edu
RID="b"
ID="b"Present address: Courant Institute of Mathematical Sciences, NYU, New York, New York 10012, USA 相似文献
10.
P. Patrício M. Tasinkevych M.M. Telo da Gama 《The European physical journal. E, Soft matter》2002,7(2):117-122
We use a two-dimensional (2D) elastic free energy to calculate the effective interaction between two circular disks immersed
in smectic-C films. For strong homeotropic anchoring, the distortion of the director field caused by the disks generates topological
defects that induce an effective interaction between the disks. We use finite elements, with adaptive meshing, to minimize
the 2D elastic free energy. The method is shown to be accurate and efficient for inhomogeneities on the length scales set
by the disks and the defects, that differ by up to 3 orders of magnitude. We compute the effective interaction between two
disk-defect pairs in a simple (linear) configuration. For large disk separations, D, the elastic free energy scales as ∼D
-2, confirming the dipolar character of the long-range effective interaction. For small D the energy exhibits a pronounced minimum. The lowest energy corresponds to a symmetrical configuration of the disk-defect
pairs, with the inner defect at the mid-point between the disks. The disks are separated by a distance that is twice the distance
of the outer defect from the nearest disk. The latter is identical to the equilibrium distance of a defect nucleated by an
isolated disk.
Received 26 October 2001 and Received in final form 14 December 2001 相似文献
11.
We consider a low-density assembly of spherical colloids, such that each is clothed by L end-grafted chemically incompatible polymer chains either of types A or B. These are assumed to be dissolved in a good common solvent. We assume that colloids are of small size to be considered as
star-polymers. Two adjacent star-polymers A and B interact through a force F originating from both excluded-volume effects and chemical mismatch between unlike monomers. Using a method developed by
Witten and Pincus (Macromolecules 19, 2509 (1986)) in the context of star-polymers of the same chemical nature, we determine exactly the force F as a function of the center-to-center distance h. We find that this force is the sum of two contributions F
e and F
s. The former, that results from the excluded volume, decays as F
e∼A
L
h
-1, with the L -dependent universal amplitude A
L∼L
3/2. While the second, which comes from the chemical mismatch, decays more slowly as F
s∼χB
L
h
-1 - τ, where τ is a critical exponent whose value is found to be τ 0.40, and χ is the standard Flory interaction parameter. We find that the corresponding L-dependent universal amplitude is B
L∼L
3 + τ
/2. Theses forces are comparable near the cores of two adjacent star-polymers, i.e. for h∼h
c∼a
(a is the monomer size). Finally, for two star-polymers of the same chemical nature (A or B), the force F that simply results from excluded-volume effects coincides exactly with F
e, and then the known result is recovered.
Received 2 October 2000 and Received in final form 24 January 2001 相似文献
12.
High aspect ratio clay particles dispersed in a lamellar matrix composed of a block copolymer or a lyotropic smectic are expected
to orient with the lamellae. Under such conditions, the smectic medium transmits elastic forces among particles in addition
to the usual forces produced by dispersion and electrostatic interactions. We compute these elastic forces and explore their
influence on the thermodynamics of lamellar-clay dispersions. It turns out that the large aspect ratio of the clay implies
a long range of interaction at the two particle level. Consequently, virial expansions break down at very low loadings of
particles. We examine the thermodynamic behavior of assemblies of flexible and rigid clay plates in both dilute and semidilute
concentration regimes. Our results should have implications for the design of nanocomposites formulated with block copolymers
and lyotropic liquid crystals.
Received 11 August 2000 相似文献
13.
Depletion interaction in a suspension of rodlike colloids with added non-adsorbing polymer coils is theoretically studied.
We calculate an overlap volume of depletion zone between two rodlike colloids, based on the second virial approximation. We
examine nematic-isotropic phase transition (NIT) and two-phase coexistence between an isotropic and a nematic phase at low
polymer concentrations. We find that the depletion interaction is dependent on the orientational order parameter of rodlike
colloids and leads to a decrease in the NIT concentration on the addition of polymer. The coexistence curves have a leaning-chimney
shape and are shifted to lower rod concentrations on increasing the polymer concentration.
Received 23 May 2001 and Received in final form 18 July 2001 相似文献
14.
A new and general approach is proposed to analyze the dynamics of a colloidal particle interacting with a nearby wall. This
analysis can be used to determine the acting forces even when the system is non-stationary. As an illustration, we use total
internal reflection microscopy to investigate the forces acting on a polystyrene sulfate latex particle as it is receding
from a charged glass surface.
Received 10 October 2002 Published online: 16 April 2003
RID="a"
ID="a"Present address: Department of Polymer Physics, BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany
RID="b"
ID="b"Present address: Arryx. Inc., Chicago, IL 60601, USA 相似文献
15.
Nadal F Argoul F Kestener P Pouligny B Ybert C Ajdari A 《The European physical journal. E, Soft matter》2002,9(4):387-399
We report a theoretical and experimental study of the hydrodynamic flow induced by an a.c. electric field in the vicinity
of a dielectric stripe deposited on a conducting plate. In the theoretical part, we model the stripe as a small change of
the surface capacitance of the plate, and a perturbative approach is used to perform the calculations. This approach predicts
an outwards rectified electro-osmotic slip along the surface that generates two steady counter-rotating rolls, the size of
which decreases with the frequency. In the experimental section, we use tracers to determine the structure of the flow and
investigate its dependence on the frequency and the amplitude of the applied voltage. The structure and amplitude of the observed
flow compares satisfactorily with the theoretical analysis. This could guide the design of surface-controlled flows and help
to understand the collective behavior of colloids near electrodes.
Received 20 June 2002
RID="a"
ID="a"e-mail: nadal@crpp.u-bordeaux.fr 相似文献
16.
V. Pot T. Karapiperis 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):387-393
We developed a numerical model based on a multi-species lattice gas cellular automaton to study passive and reactive tracer
migration in saturated geological media. The model was made of multiple lattice gases interacting via a two-species collision rule. For a binary mixture, the model displayed a negative deviation from Raoult's law and therefore
behaved as a real solution. By biasing the initial two-species collision rule, our model was made to obey the tracer assumption
which requires that the tracer species does not affect the velocity of the vehicle fluid. In a 2D fracture, we checked the
Taylor-Aris relation. An irreversible adsorption between the tracer and the solid phase was numerically added to perform filtration
of the colloids. A good agreement was found with the solution of the filtration equation. An attachment efficiency was defined
and was found to bear a linear relationship to the filtration coefficient. We added a third species to study the potential
role of colloids in the transport of contaminants. Contaminant migration was enhanced when contaminants were bound to colloids
and was slightly reduced when colloids were allowed to adsorb on the solid phase.
Received 14 January 1999 and Received in final form 8 June 1999 相似文献
17.
The flow birefringence and the rheological properties of four viscoelastic solutions having nearly the same zero shear viscosity
and subjected to shear flows are investigated in the linear and non-linear domains. The surfactant used for the samples is
the cetyltrimethylammonium chloride in water at the concentration of 100 mmol/l with an organic salt, the sodium salicylate.
The low shear viscosity curve versus the salt concentration is non-monotonic and has two maxima separated by a minimum forming four domains in which the salt
concentration is chosen. For the two solutions belonging to the inner branch, i.e. between the two maxima, a simple Maxwellian behaviour is observed and shear banding occurs as confirmed by the flow birefringence
pictures. Contrary to the results of P. Fisher (1996) where the unstable flow regime is restricted to the first decreasing
part of the low shear viscosity curve of a cetylpyridinium chloride solution, we show that shear banding exits in a wider
domain of the salt concentration.
Received 18 November 2002 / Published online: 1 April 2003
RID="a"
ID="a"e-mail: Decruppe@lpli.sciences.univ-metz.fr 相似文献
18.
The static structure factor (S(q)) of dispersions and gels of disk-like mineral colloids (Laponite) was investigated using time- and ensemble-averaged light
scattering. The evolution of S(q) in time after increasing the ionic strength of well-dispersed Laponite suspensions shows that Laponite aggregates and forms
fractal clusters. The structure of the aggregates does not depend on the ionic strength, but the rate of growth increases
very strongly with the ionic strength. At concentrations below about 3 g/l (0.12% v/v) the aggregates sediment while at higher
concentrations space-filling gels are formed. The gels are homogeneous on length scales larger than the correlation length
which decreases strongly with decreasing ionic strength and increasing concentration. However, the local structure is the
same, independent of the concentration and the ionic strength.
Received 6 August 2000 and Received in final form 16 March 2001 相似文献
19.
B.R. McClain M. Yoon J.D. Litster S.G.J. Mochrie 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):45-52
Measurements are presented of the X-ray specular reflectivity and near-specular diffuse scattering of the interface in a near-critical
mixture of hexane and perfluorohexane. A lineshape analysis of the scattered intensity at each temperature yields values for
the interfacial tension and interfacial width. The temperature variation of the tension and width so-obtained are consistent
with current understanding of this interface, which holds that there is, firstly, an intrinsic width over which the fluid
density varies smoothly from one coexistence composition to the other, and, secondly, that the interface acquires an additional
and larger statistical interfacial width as a result of capillary fluctuations.
Received 1 April 1998 相似文献
20.
Bruinsma RF 《The European physical journal. E, Soft matter》2006,19(3):303-310
The overview discusses the application of physical arguments to structure and function of single-stranded viral RNA genomes. 相似文献