54 research outputs found
Thermodiffusion in binary liquids: the role of irreversibility
We study thermal diffusion in binary mixtures in the framework of
non-equilibrium thermodynamics. Our formal result displays the role of partial
enthalpies and Onsager's generalized mobilities. The mobility ratio provides a
measure for the irreversible character of thermal diffusion. Comparison with
experimental data on benzene, cyclohexane, toluene and alkanes shows that
irreversibility is essential for thermal diffusion, and in particular for the
isotope effect.Comment: 7 pages, 2 figure
On the thermopower of ionic conductor and ionic capacitors
We theoretically study the thermoelectric response of ionic conductors to an
applied temperaturegradient. As a main result we find that open and closed
systems with respect to charge exchange,result in different expressions for the
thermopower which may even take opposite signs. For theexperimentally most
relevant zero-current steady state, we show that the thermopower of ionic
conductorsdoes not depend on the mobilities, contrary to what is known for
metals and semiconductors.The different behavior of ionic and electronic
conductors is traced back to the unlike conservationlaws for ionic carriers and
electron-hole pairs
Polarization of active Janus particles
We study the collective motion of Janus particles in a temperature or
concentration gradient. Because of the torque exerted by an external or
self-generated field, the particles align their axis on this gradient. In a
swarm of self-driven particles, this polarization enhances the
interactiondriven confinement. Self-polarization in a non-uniform laser beam
could be used for guiding hot particles along a given trajectory.Comment: 5 pages, 2 figure
Dynamics of a spherical colloid at a liquid interface:A lattice Boltzmann study
We study the dynamics of a spherical colloidal particle pulled along the fluid-fluid interface using lattice Boltzmann (LB) simulations. We consider an interface with a finite width and include both the effects of the thermodynamics of the interface and the particle wetting, characterized by the contact angle h between the particle surface and the interface, in addition to the viscosity ratio k between the two fluids. We characterize the particle dynamics by applying a constant pulling force along the interface and measure both the translational and the rotational dynamics as a function of the contact angle and the viscosity ratio. We observe that the hydrodynamic drag is reduced and the particle rotation is increased when the particle resides more in the low viscosity fluid, in agreement with previous hydrodynamic theories. We also study the case where the particle rotation is suppressed, and find an overall increase of the drag coefficient
Elastic response of [111]-tunneling impurities
We study the dynamic response of a [111] quantum impurity, such as lithium or
cyanide in alkali halides, with respect to an external field coupling to the
elastic quadrupole moment. Because of the particular level structure of a
eight-state system on a cubic site, the elastic response function shows a
biexponential relaxation feature and a van Vleck type contribution with a
resonance frequency that is twice the tunnel frequency . This
basically differs from the dielectric response that does not show relaxation.
Moreover, we show that the elastic response of a [111] impurity cannot be
reduced to that of a two-level system. In the experimental part, we report on
recent sound velocity and internal friction measurements on KCl doped with
cyanide at various concentrations. At low doping (45 ppm) we find the dynamics
of a single [111] impurity, whereas at higher concentrations (4700 ppm) the
elastic response rather indicates strongly correlated defects. Our theoretical
model provides a good description of the temperature dependence of
and at low doping, in particular the relaxation peaks, the absolute
values of the amplitude, and the resonant contributions. From our fits we
obtain the value of the elastic deformation potential eV.Comment: 19 pages, 5 figure
Non-equilibrium Properties of an Active Nanoparticle in a Harmonic Potential
Active particles break out of thermodynamic equilibrium thanks to their
directed motion, which leads to complex and interesting behaviors in the
presence of confining potentials. When dealing with active nanoparticles,
however, the overwhelming presence of rotational diffusion hinders directed
motion, leading to an increase of their effective temperature, but otherwise
masking the effects of self-propulsion. Here, we demonstrate an experimental
system where an active nanoparticle immersed in a critical solution and held in
an optical harmonic potential features far-from-equilibrium behavior beyond an
increase of its effective temperature. When increasing the laser power, we
observe a cross-over from a Boltzmann distribution to a non-equilibrium state,
where the particle performs fast orbital rotations about the beam axis. These
findings are rationalized by solving the Fokker-Planck equation for the
particle's position and orientation in terms of a moment expansion. The
proposed self-propulsion mechanism results from the particle's non-sphericity
and the lower critical point of the solute.Comment: 6 figure
Thermophoresis of charged colloidal particles
Thermally induced particle flow in a charged colloidal suspension is studied
in a fluid-mechanical approach. The force density acting on the charged
boundary layer is derived in detail. From Stokes' equation with no-slip
boundary conditions at the particle surface, we obtain the particle drift
velocity and the thermophoretic transport coefficients. The results are
discussed in view of previous work and available experimental data.Comment: 9 pages, 2 figure
Thermally driven Marangoni surfers
We study autopropulsion of an interface particle that is driven by the Marangoni stress arising from a self-generated asymmetric temperature or concentration field. We calculate separately the long-range Marangoni flow vI due to the stress discontinuity at the interface and the short-range velocity field vP imposed by the no-slip condition on the particle surface. Both contributions are evaluated for a spherical floater with temperature monopole and dipole moments. We find that the self-propulsion velocity is given by the amplitude of the 'source doublet' that belongs to the short-range contribution vP. Hydrodynamic interactions, on the other hand, are determined by the long-range Marangoni flow vI . Its dipolar part results in an asymmetric advection pattern of neighbouring particles, which in turn may perturb the known hexatic lattice or even favour disordered states
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