2,426 research outputs found

### Histogram analysis as a method for determining the line tension by Monte-Carlo simulations

A method is proposed for determining the line tension, which is the main
physical characteristic of a three-phase contact region, by Monte-Carlo (MC)
simulations. The key idea of the proposed method is that if a three-phase
equilibrium involves a three-phase contact region, the probability distribution
of states of a system as a function of two order parameters depends not only on
the surface tension, but also on the line tension. This probability
distribution can be obtained as a normalized histogram by appropriate MC
simulations, so one can use the combination of histogram analysis and
finite-size scaling to study the properties of a three phase contact region.
Every histogram and results extracted therefrom will depend on the size of the
simulated system. Carrying out MC simulations for a series of system sizes and
extrapolating the results, obtained from the corresponding series of
histograms, to infinite size, one can determine the line tension of the three
phase contact region and the interfacial tensions of all three interfaces (and
hence the contact angles) in an infinite system. To illustrate the proposed
method, it is applied to the three-dimensional ternary fluid mixture, in which
molecular pairs of like species do not interact whereas those of unlike species
interact as hard spheres. The simulated results are in agreement with
expectations

### An Equation of State of Gases at High Temperatures and Densities

State equation of molecular gas at high temperatures and densitie

### Formation of capillary bridges in AFM-like geometry

We discuss the phase diagram of fluid confined in AFM-like geometry. It
combines the properties of capillary condensation and complete filling of a
wedge.Comment: 9 pages, 7 figure

### Stability of freely falling granular streams

A freely falling stream of weakly cohesive granular particles is modeled and
analysed with help of event driven simulations and continuum hydrodynamics. The
former show a breakup of the stream into droplets, whose size is measured as a
function of cohesive energy. Extensional flow is an exact solution of the
one-dimensional Navier-Stokes equation, corresponding to a strain rate,
decaying like 1/t from its initial value, gammaDot0. Expanding around this
basic state, we show that the flow is stable for short times (gammaDot0 * t <<
1), whereas for long times (gammaDot0 * t >> 1) perturbations of all wavelength
grow. The growthrate of a given wavelength depends on the instant of time when
the fluctuation occurs, so that the observable patterns can vary considerably.Comment: 4 page, 5 figures. Submitted to PRL. Supplementary material: see
http://wwwuser.gwdg.de/~sulrich/research/#Publication

### The influence of line tension on the formation of liquid bridges

The formation of liquid bridges between a planar and conical substrates is
analyzed macroscopically taking into account the line tension. Depending on the
value of the line tension coefficient \tau and geometric parameters of the
system one observes two different scenarios of liquid bridge formation upon
changing the fluid state along the bulk liquid-vapor coexistence. For \tau >
\tau * (\tau * < 0) there is a first-order transition to a state with
infinitely thick liquid bridge. For \tau < \tau * the scenario consists of two
steps: first there is a first-order transition to a state with liquid bridge of
finite thickness which upon further increase of temperature is followed by
continuous growth of the thickness of the bridge to infinity. In addition to
constructing the relevant phase diagram we examine the dependence of the width
of the bridge on thermodynamic and geometric parameters of the system.Comment: 4 pages, 5 figure

### Reply to Comment on: "Are stress-free membranes really 'tensionless'?"

This is a reply to a comment on the paper arXiv:1204.2075 "Are stress-free
membranes really tensionless ?" (EPL 95,28008 (2011))

### Surface tension of electrolytes: Hydrophilic and hydrophobic ions near an interface

We calculate the ion distributions around an interface in fluid mixtures of
highly polar and less polar fluids (water and oil) for two and three ion
species. We take into account the solvation and image interactions between ions
and solvent. We show that hydrophilic and hydrophobic ions tend to undergo a
microphase separation at an interface, giving rise to an enlarged electric
double layer. We also derive a general expression for the surface tension of
electrolyte systems, which contains a negative electrostatic contribution
proportional to the square root of the bulk salt density. The amplitude of this
square-root term is small for hydrophilic ion pairs, but is much increased for
hydrophilic and hydrophobic ion pairs. For three ion species including
hydrophilic and hydrophobic ions, we calculate the ion distributions to explain
those obtained by x-ray reflectivity measurements.Comment: 8 figure

### Sedimentation of a two-dimensional colloidal mixture exhibiting liquid-liquid and gas-liquid phase separation: a dynamical density functional theory study

We present dynamical density functional theory results for the time evolution
of the density distribution of a sedimenting model two-dimensional binary
mixture of colloids. The interplay between the bulk phase behaviour of the
mixture, its interfacial properties at the confining walls, and the
gravitational field gives rise to a rich variety of equilibrium and
non-equilibrium morphologies. In the fluid state, the system exhibits both
liquid-liquid and gas-liquid phase separation. As the system sediments, the
phase separation significantly affects the dynamics and we explore situations
where the final state is a coexistence of up to three different phases. Solving
the dynamical equations in two-dimensions, we find that in certain situations
the final density profiles of the two species have a symmetry that is different
from that of the external potentials, which is perhaps surprising, given the
statistical mechanics origin of the theory. The paper concludes with a
discussion on this

### Phase separation dynamics in a two-dimensional magnetic mixture

Based on classical density functional theory (DFT), we investigate the
demixing phase transition of a two-dimensional, binary Heisenberg fluid
mixture. The particles in the mixture are modeled as Gaussian soft spheres,
where one component is characterized by an additional classical spin-spin
interaction of Heisenberg type. Within the DFT we treat the particle
interactions using a mean-field approximation. For certain magnetic coupling
strengths we calculate phase diagrams in the density-concentration plane. For
sufficiently large coupling strengths and densities, we find a demixing phase
transition driven by the ferromagnetic interactions of the magnetic species. We
also provide a microscopic description (i.e., density profiles) of the
resulting non-magnetic/magnetic fluid-fluid interface. Finally, we investigate
the phase separation using dynamical density functional theory (DDFT),
considering both nucleation processes and spinodal demixing.Comment: 15 pages, 10 figure

### Are stress-free membranes really 'tensionless'?

In recent years it has been argued that the tension parameter driving the
fluctuations of fluid membranes, differs from the imposed lateral stress, the
'frame tension'. In particular, stress-free membranes were predicted to have a
residual fluctuation tension. In the present paper, this argument is
reconsidered and shown to be inherently inconsistent -- in the sense that a
linearized theory, the Monge model, is used to predict a nonlinear effect.
Furthermore, numerical simulations of one-dimensional stiff membranes are
presented which clearly demonstrate, first, that the internal 'intrinsic'
stress in membranes indeed differs from the frame tension as conjectured, but
second, that the fluctuations are nevertheless driven by the frame tension.
With this assumption, the predictions of the Monge model agree excellently with
the simulation data for stiffness and tension values spanning several orders of
magnitude

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