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@INPROCEEDINGS{Wiegand:819853,
      author       = {Wiegand, Simone},
      title        = {{U}se of thermal gradients in (aqueous) soft matter
                      systems},
      reportid     = {FZJ-2016-05432},
      year         = {2016},
      abstract     = {In many experimental situations temperature gradients play
                      an important role. For almost one century
                      thermogravitational columns and thermal field flow
                      fractionation channels have been used for separation and
                      characterization of soft matter [1]. Presently researchers
                      design synthetic microswimmers, micromotors, or micropumps
                      to explore possibilities to recycle waste heat using such
                      microfluidic devices [2]. So far there is only a limited
                      microscopic understanding of thermodiffusion or
                      thermophoresis in simple and complex fluids. In the recent
                      years some progress has been made for non-polar systems, but
                      in aqueous systems the situation is complicated due to
                      charge effects and strong specific cross interactions so
                      that simple thermodynamic concepts fail. On the other hand a
                      detailed understanding of aqueous systems would be valuable
                      due to important applications in biotechnology, where the
                      response to temperature gradients is successfully employed
                      to monitor the reaction kinetics of large proteins with
                      small ligand molecules. The strong sensitivity of proteins
                      and other water soluble biomolecules is probably caused by a
                      change in the hydration layer, which is influenced by subtle
                      conformation changes induced by the binding of the ligand
                      molecule. To get a better understanding we systematically
                      investigated various small water soluble molecules,
                      microemulsions and colloids by a holographic grating method
                      called infrared thermal diffusion forced Rayleigh scattering
                      (IR-TDFRS). In order to elucidate the mechanism in
                      biomolecules we performed systematic measurements of amides,
                      which often serve as model systems for peptide bonds, an
                      essential structure in proteins. Using the experimental data
                      determined for fomamide we perform numerical finite-element
                      simulations in hydrothermal pores and show that a
                      combination of thermophoresis and convection can lead to
                      accumulation of formamide up to concentrations where
                      nucleobases are formed [3], which might serve as an
                      ‘origin-of-life’ scenario. Further we study
                      microemulsion droplets as soft colloids to investigate the
                      relation between the interfacial tension and the Soret
                      coefficient [4]. Other important contributions in aqueous
                      systems are charge effects, which we study systematically
                      for colloidal model systems. Using a theoretical model by
                      Dhont and Briels [5] valid for spherical charged colloids
                      with arbitrary double-layer thicknesses we are able to
                      calculate the surface charge density of the colloid. It
                      turns out that the surface charge density agrees well with
                      electrophoresis measurements. The same holds for an extended
                      model for charged colloidal rods [6]. [1] Wiegand, S., in
                      Functional Soft Matter, J.K.G. Dhont, et al., Editors. 2015,
                      Forschungszentrum Jülich. F4.[2] Ripoll, M. and Yang, M.C.,
                      in World Scientific Lecture Notes in Complex Systems - Vol.
                      12Engineering of Chemical Complexity II (2015) 109.[3]
                      Niether, D., Afanasenkau, D., Dhont, J.K.G. and Wiegand, S.
                      , PNAS, 113 (2016) 4272.[4] Naumann, Ph., Datta, S.,
                      Sottmann, T., Arlt, B., Frielinghaus, H., Wiegand, S., J .
                      Phys. Chem. B, 118 (2014) 3451.[5] Dhont, J.K.G. and Briels,
                      W.J., Eur. Phys. J. E, 25 (2008) 61.[6] Wang, Z., Kriegs,
                      H., Buitenhuis, J., Dhont, J.K.G., Wiegand, S., Soft Matter,
                      9 (2013) 8697.},
      month         = {Sep},
      date          = {2016-09-29},
      organization  = {Kolloquium, Tokai University, Tokai
                       (Japan), 29 Sep 2016 - 29 Sep 2016},
      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)31},
      url          = {https://juser.fz-juelich.de/record/819853},
}