12,604 research outputs found
Disjoining Pressure of an Electrolyte Film Confined between Semipermeable Membranes
We consider an electrolyte solution confined by semipermeable membranes in
contact with a salt-free solvent. Membranes are uncharged, but since small
counter-ions leak-out into infinite salt-free reservoirs, we observe a
distance-dependent membrane potential, which generates a repulsive
electrostatic disjoining pressure. We obtain the distribution of the potential
and of ions, and derive explicit formulas for the disjoining pressure, which
are validated by computer simulations. We predict a strong short-range
power-law repulsion, and a weaker long-range exponential decay. Our results
also demonstrate that an interaction between membranes does strongly depend on
the screening lengths, valency of an electrolyte solution, and an
inter-membrane film thickness. Finally, our analysis can be directly extended
to the study of more complex situations and some biological problems.Comment: 9 pages, 8 figure
Electrostatic Interaction of Heterogeneously Charged Surfaces with Semipermeable Membranes
In this paper we study the electrostatic interaction of a heterogeneously
charged wall with a neutral semipermeable membrane. The wall consists of
periodic stripes, where the charge density varies in one direction. The
membrane is in a contact with a bulk reservoir of an electrolyte solution and
separated from the wall by a thin film of salt-free liquid. One type of ions
(small counterions) permeates into the gap and gives rise to a
distance-dependent membrane potential, which translates into a repulsive
electrostatic disjoining pressure due to an overlap of counterion clouds in the
gap. To quantify it we use two complementary approaches. First, we propose a
mean-field theory based on a linearized Poisson-Boltzmann equation and Fourier
analysis. These calculations allow us to estimate the effect of a heterogeneous
charge pattern at the wall on the induced heterogeneous membrane potential, and
the value of the disjoining pressure as a function of the gap. Second, we
perform Langevin dynamics simulations of the same system with explicit ions.
The results of the two approaches are in good agreement with each other at low
surface charge and small gap, but differ due to nonlinearity at the higher
charge. These results demonstrate that a heterogeneity of the wall charge can
lead to a huge reduction in the electrostatic repulsion, which could
dramatically facilitate a self-assembly in complex synthetic and biological
systems.Comment: 14 pages, 6 figure
Star polymers as unit cells for coarse-graining cross-linked networks
Reducing the complexity of cross-linked polymer networks by preserving their
main macroscale properties, is key to understanding them, and a crucial issue
is to relate individual properties of the polymer constituents to those of the
reduced network. Here we study polymer networks in a good solvent, by
considering star polymers as their unit elements, and first quantify the
interaction between their centers of masses. We then reduce the complexity of a
network by replacing sets of its bridged star polymers by equivalent effective
soft particles with dense cores. Our coarse graining allows us to approximate
complex polymer networks by much simpler ones, keeping their relevant
mechanical properties, as illustrated in computer experiments on an isotropic
compression.Comment: 5 pages, 8 figure
The establishment of Diachasmimorpha longicaudata (Hymenoptera: Braconidae) in Misiones, Northeastern Argentina
The establishment of Diachasmimorpha longicaudata (Ashmead) on Anastrepha fraterculus (Wiedemann) in the northeastern province of Misiones, Argentina, is described.Fil: Schliserman, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Fundación Miguel Lillo. Centro de Investigaciones para la Regulación de Poblaciones de Organismos Nocivos; ArgentinaFil: Ovruski Alderete, Sergio Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Fundación Miguel Lillo. Centro de Investigaciones para la Regulación de Poblaciones de Organismos Nocivos; ArgentinaFil: De Coll, Olga R.. Instituto Nacional de Tecnología Agropecuaria; Argentin
How Geometry Controls the Tearing of Adhesive Thin Films on Curved Surfaces
Flaps can be detached from a thin film glued on a solid substrate by tearing
and peeling. For flat substrates, it has been shown that these flaps
spontaneously narrow and collapse in pointy triangular shapes. Here we show
that various shapes, triangular, elliptic, acuminate or spatulate, can be
observed for the tears by adjusting the curvature of the substrate. From
combined experiments and theoretical models, we show that the flap morphology
is governed by simple geometric rules.Comment: 6 pages, 5 figure
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