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@INPROCEEDINGS{Wiegand:256304,
      author       = {Wiegand, Simone and Afanasenkau, Dzmitry and Wang, Zilin
                      and Buitenhuis, Johan and Dhont, Jan K.G.},
      title        = {{T}hermophoresis of charged colloidal spheres and rods},
      school       = {Uni. Cavite, Philippines},
      reportid     = {FZJ-2015-06268},
      year         = {2015},
      abstract     = {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 Soret coefficient of the fd-viruses
                      increases monotonically with increasing Debye length, 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]. 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.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 et al.,
                      Soft Matter, 9, 8697(2013).[4] S. Wiegand, H. Ning, and H.
                      Kriegs, J. Phys. Chem. B, 111, 14169(2007). Keywords:
                      Thermophoresis, colloids, aqueous mixtures, holographic
                      grating technique, microfluidic},
      month         = {Oct},
      date          = {2015-10-22},
      organization  = {2015 International Meeting for optical
                       Manipulation in Complex Systems, Cavite
                       (Philippines), 22 Oct 2015 - 24 Oct
                       2015},
      subtyp        = {Invited},
      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/256304},
}