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@INPROCEEDINGS{Wiegand:204999,
      author       = {Wiegand, Simone and Afanasenkau, Dzmitry and Syshchyk, Olga
                      and Wang, Zilin and Buitenhuis, Johan and Dhont, Jan K.G.},
      title        = {{T}hermophoresis of charged colloidal spheres and rods},
      reportid     = {FZJ-2015-05504},
      year         = {2015},
      abstract     = {Thermophoresis or Thermal diffusion, which is also known as
                      the Ludwig–Soret effect, is the phenomenon where mass
                      transport is induced by a temperature gradient in a
                      multi-component system. So far there is no microscopic
                      understanding for fluids. In the recent years the « heat of
                      transfer » concept has been successfully applied to
                      non-polar systems, but in aqueous systems the situations is
                      complicated due to charge effects and strong specific cross
                      interactions so that this concept fails.Recently Dhont and
                      Briels [1] calculated the double-layer contribution to the
                      single-particle thermal diffusion coefficient of charged,
                      spherical colloids with arbitrary double-layer thickness. In
                      this approach three forces are taken into account, which
                      contribute to the total thermophoretic force on a charged
                      colloidal sphere due its double layer: i) the force FW that
                      results from the temperature dependence of the internal
                      electrostatic energy W of the double layer, ii) the electric
                      force Fel with which the temperature-induced non-spherically
                      symmetric double-layer potential acts on the surface charges
                      of the colloidal sphere and iii) the solvent-friction force
                      Fsol on the surface of the colloidal sphere due to the
                      solvent flow that is induced in the double layer because of
                      its asymmetry. This concept has successfully been used to
                      describe the Soret coefficient of Ludox particles as
                      function of the Debye length [2] (cf. Fig. 1). The surface
                      charge density of the Ludox particles is independently
                      obtained from electrophoresis measurements, the size of the
                      colloidal particles is obtained from electron microscopy,
                      and the Debye length is calculated from the ion
                      concentration. Therefore the only adjustable parameter in
                      the comparison with theory is the intercept at zero Debye
                      length, which measures the contribution to the Soret
                      coefficient of the solvation layer and possibly the colloid
                      core material.Later the concept was extended for charged
                      colloidal rods [3]. As model system we used the charged,
                      rod-like fd-virus. The wild type fd-virus has a contour
                      length L of 880 nm, a radius R of 3.4 nm, and a persistence
                      length LP of 2.2 µm. The Soret coefficient of the
                      fd-viruses increases monotonically with increasing Debye
                      length (cf. Fig. 1), while there is a relatively weak
                      dependence on the rod-concentration when the ionic strength
                      is kept constant. Additionally to the intercept at zero
                      Debye length we used the surface charge density as an
                      adjustable parameter. Experimentally we found a surface
                      charge density of 0.0500.003 e/nm2, which compares well
                      the surface charge density, of 0.0660.004 e/nm2, which
                      has been determined by electrophoresis measurements taking
                      into account the ion condensation.All experiments so far
                      have been performed with the so-called infrared thermal
                      diffusion forced Rayleigh scattering technique [4], with a
                      writing wavelength of 980 nm, which corresponds to an
                      absorption band of water with an approximate optical density
                      equal to OD=0.5 cm-1. This method uses the refractive index
                      contrast between the different components and is therefore
                      typically limited to binary mixtures. In order to study also
                      biological colloids in buffer solutions we are presently
                      developing a microscopic cell with heated wires. First
                      results for some fluorescently labelled polystyrene lattices
                      in the microwire cell are presented in comparison with
                      thermal diffusion forced Rayleigh scattering measurements.
                      Figure 1: (A) Soret coefficient, ST, as function of the
                      Debye length for Ludox particles and the wild type fd-virus.
                      (B) TEM image of the Ludox particle and (C) the
                      corresponding size distribution. (D) TEM image of the
                      fd-virus.REFERENCES[1] J.K.G. Dhont and W.J. Briels, Eur.
                      Phys. J. E 25, 61(2008).[2] H. Ning, J.K.G. Dhont, and S.
                      Wiegand, Langmuir, 24, 2426(2008).[3] Z. Wang, H. Kriegs, J.
                      Buitenhuis, J.K.G. Dhont, and S. Wiegand, Soft Matter, 9,
                      8697(2013).[4] S. Wiegand, H. Ning, and H. Kriegs, J. Phys.
                      Chem. B, 111, 14169(2007).},
      month         = {May},
      date          = {2015-05-20},
      organization  = {Joint European Thermodynamics
                       Conference 2015, Nancy (France), 20 May
                       2015 - 22 May 2015},
      subtyp        = {After Call},
      cin          = {ICS-3},
      cid          = {I:(DE-Juel1)ICS-3-20110106},
      pnm          = {551 - Functional Macromolecules and Complexes (POF3-551)},
      pid          = {G:(DE-HGF)POF3-551},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/204999},
}