14 research outputs found
Comparing open and closed molecular self-assembly
We study theoretically in the present work the self-assembly of molecules in
an open system, which is fed by monomers and depleted in partial or complete
clusters. Such a scenario is likely to occur for example in the context of
viral self-assembly. We provide a general formula for the mean-field size
distribution which is valid both at equilibrium in a closed system, and in the
stationary state in an open system. This allows us to explore in a simple way
out-of-equilibrium features for self-assembly and compare them to equilibrium
properties. In particular, we identify a region of parameter space for which
the out-of-equilibrium size distribution in the presence of external fluxes is
equal to the equilibrium size distribution in the absence of external fluxes,
up to a constant renormalization factor. The range of validity of this result
and its consequences are discussed.Comment: PACS 81.16.Fg - Supramolecular and biochemical assembly PACS 82.39.-k
- Chemical kinetics in biological systems PACS 05.65.+b - Self-organized
system
Electric-field induced capillary interaction of charged particles at a polar interface
We study the electric-field induced capillary interaction of charged
particles at a polar interface. The algebraic tails of the electrostatic
pressure of each charge results in a deformation of the interface . The resulting capillary interaction is repulsive and varies as with the particle distance. As a consequence, electric-field induced
capillary forces cannot be at the origin of the secondary minimum observed
recently for charged PMMA particles at on oil-water interface.Comment: June 200
Charged inclusion in nematic liquid crystals
We present a general theory of liquid crystals under inhomogeneous electric
field in a Ginzburg-Landau scheme. The molecular orientation can be deformed by
electric field when the dielectric tensor is orientation-dependent. We then
investigate the influence of a charged particle on the orientation order in a
nematic state. The director is aligned either along or perpendicular to the
local electric field around the charge, depending on the sign of the dielectric
anisotropy. The deformation becomes stronger with increasing the ratio ,
where is the charge and is the radius of the particle. Numerical
analysis shows the presence of defects around the particle for large .
They are nanometer-scale defects for microscopic ions. If the dielectric
anisotropy is positive, a Saturn ring defect appears. If it is negative, a pair
of point defects appear apart from the particle surface, each being connected
to the surface by a disclination line segment.Comment: 12 figure
ER Membrane Phospholipids and Surface Tension Control Cellular Lipid Droplet Formation
Effets de charge discrète aux interfaces d'un électrolyte confiné
Dans un film électrolyte plan, lorsque la distance entre les charges de surface excède la longueur d'écrantage, l'approximation de distribution continue de charge de surface ne s'applique plus. Il faut prendre en compte la nature discrète des charges. Dans une géométrie interfaciale, l'écrantage de charges ponctuelles n'est pas exponentiel mais algébrique ; la densité de charges d'écrans et le potentiel d'interaction écranté variant en r-3. En conséquence : (i) Il y a étalement du nuage d'écrantage qui dans un film électrolyte fin peut alors avoir une largeur typique bien supérieur à la longueur de Debye. (ii) L'interaction entre les charges est à longue portée malgré l'écrantage ; nous montrons que, malgré la dépendance en r-3, il ne s'agit pas d'une interaction dipolaire. Lorsque la nature discrète des charges est pertinente, la pression s'exerçant sur les interfaces du film diffère de celle de surface chargée de manière homogène. La pression provient, dans ce cas, de la force exercée par chaque charge discrète et varie, en conséquence, linéairement avec la densité de charge. La pression des charges discrète est très inhomogène et peut induire des déformations lorsque les interfaces sont "molles". Deux charges induisent deux déformations de l'interface qui vont interagir. Nous montrons que les déformations de deux charges sur une interface liquide se repoussent. Cet effet n'est donc pas à l'origine de l'attraction entre charges de surface observée expérimentalement récemment.In an electrolyte film, if the lateral surface charge distance exceeds the screening length, the standard continuous approximation for the charge distribution fails. The discrete nature of the charge has to be taken into account. In interfacial geometries, screening of punctual charge is no longer exponential but algebraic ; the screening cloud charge density and the screened potential decay as r-3. As a consequence: (i) The screening cloud is spread along the interface and can reach a typical lateral length larger than the Debye length. (ii) There is a long-range interaction between the charges. We have shown that despite the r-3 law, this is not a dipolar interaction. If the discreteness of the charge is relevant, the disjoining pressure of the film deviates from that of homogeneously charged surfaces. The pressure is now due to the force created by each discrete charge and is thus, linear in surface charge density. The pressure of the discrete charges is strongly inhomogeneous and may deform "soft" interfaces. The deformations superposition induces an effective interaction of the surface charges. We have shown that the effective interaction of two charges on a liquid interface is repulsive. Thus, this force is not responsible for the charges attraction observed in recent experiments
Shape and energy of a membrane bud induced by protein coats or viral protein assembly
Intracellular transport vesicles and enveloped virus production is mediated by the polymerization of proteins that form bi-dimensional curved and rigid structures, or “coats”, on a membrane. Using the classical framework of fluid membrane elasticity, we compute numerically the shape and the mechanical energy of the membrane deformation induced by a coat at different stage of growth. We furthermore derive analytical approximate expressions for the membrane shape and energy. They are found to be very accurate when compared to numerical calculations. These analytical expressions should be useful when building a relevant model of coat polymerization kinetics. We also discuss some consequences of the membrane energy features on the coat assembly process, showing that at high tension a kinetically arrested state of incomplete assembly could exist
Long-range interactions of surface charges on electrolyte films
International audienceA surface charge at an electrolyte–insulator interface and its counterion cloud form an electric dipole, thus giving rise to a long-range interaction that has been identified as the usual dipolar interaction. In this paper, we show that the picture of interacting dipoles ceases to be valid for a thin film with a thickness smaller than the Debye screening length. Indeed, in this case, both parallel and antiparallel dipoles repel each other, with a force much stronger than expected from a dipolar interaction. This originates from the delocalization of the screening clouds in very thin films
Electric-Field Induced Capillary Interaction of Charged Particles at a Polar Interface
We study the electric-field induced capillary interaction of charged particles at a polar interface. The algebraic tails of the electrostatic pressure of each charge results in a deformation of the interface . The resulting capillary interaction\ is repulsive and varies as with the particle distance. As a consequence, electric-field induced capillary forces cannot be at the origin of the secondary minimum observed recently for charged PMMA particles at on oil-water interface
Modeling the Kinetics of Open Self-Assembly
In this work, we
explore theoretically the kinetics of molecular
self-assembly in the presence of constant monomer flux as an input,
and a maximal size. The proposed model is supposed to reproduce the
dynamics of viral self-assembly for enveloped virus. It turns out
that the kinetics of open self-assembly is rather quantitatively different
from the kinetics of similar closed assembly. In particular, our results
show that the convergence toward the stationary state is reached through
assembly waves. Interestingly, we show that the production of complete
clusters is much more efficient in the presence of a constant input
flux, rather than providing all monomers at the beginning of the self-assembly