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@PHDTHESIS{Lang:860717,
      author       = {Lang, Christian},
      title        = {{D}ynamics and phase behavior of (non-)ideal liquid
                      crystals under shear},
      school       = {KU Leuven},
      type         = {Dissertation},
      reportid     = {FZJ-2019-01382},
      pages        = {162},
      year         = {2019},
      note         = {Dissertation, KU Leuven, 2019},
      abstract     = {As the simplest form of polymeric materials, rodlike
                      polymers provide a unique opportunity to test and review the
                      theory of polymer dynamics. Liquid crystalline solutions of
                      rodlike particles are of high industrial relevance and their
                      flow behavior during processing strongly influences the
                      properties of the final products.While industrially used
                      materials are mostly non-ideal in several aspects such as
                      flexibility and polydispersity of the particles, the theory
                      of polymer dynamics is best applicable only to ideal rods.
                      The attempt of this thesis is to provide new insights into
                      the effect of such non-ideality parameters on the flow
                      behavior of rodlike suspensions.Rodlike bacteriophages are
                      used in this work in order to formulate materials with
                      well-defined system characteristics, which can be alternated
                      in a controlled way to understand non-ideal suspensions of
                      rods. These rodlike viruses form various liquid-crystalline
                      phases in aqueous suspension. However, here we focus on
                      isotropic suspensions which have neither positional nor
                      orientational order in the equilibrium state.The dynamics
                      and phase behavior of suspensions in the isotropic state are
                      measured under flow by means of a combination of small angle
                      neutron scattering with rheology and heterodyne dynamic
                      light scattering under flow. Based on the experimental
                      outcome, the theory of rodlike polymers is reviewed.In
                      chapter 2, a revised theory for ideal rodlike particles is
                      derived and tested in chapter 4. In chapter 5, we test the
                      theory against the influence of non-ideality parameters to
                      gain a deeper understanding of the nature of these
                      influences. Particularly, new expressions for the rotational
                      diffusion coefficient under tube dilation and a
                      non-equilibrium pair-correlation function are derived to
                      supplement the Fokker-Planck equation for rods.In chapter 5,
                      it is shown theoretically as well as experimentally that
                      particle morphology is one of the key influences on the flow
                      behavior of rods. In this respect, length and flexibility
                      are two counteracting parameters. With increasing length,
                      the dynamics of the rods slow down significantly leading to
                      higher zero shear viscosities, while an increase of particle
                      flexibility has the opposite effect. Furthermore, the onset
                      of shear thinning depends crucially on the particle length.
                      An increase in length shifts the onset of shear thinning to
                      smaller shear-rates. In section 5.3.2, we use the
                      understanding of this length dependence to make our
                      theoretical predictions quantitative by experimentally
                      determining the prefactor of the rotational diffusion
                      coefficient in the tube model for the first time. This is
                      very useful, as it is the basis for the understanding of
                      other phenomena studied here and reported in literature. Due
                      to a morphological transition to a hairpin state, an
                      increase in flexibility causes an increase of the viscosity
                      in the intermediate and high shear-rate regime, such that
                      under strong flow, higher length and higher bending rigidity
                      are both promoting shear thinning.In sections 4.3.1 and 5.2,
                      small amplitude oscillatory shear is used to demonstrate
                      that the rotational diffusion and the particle flexibility
                      crucially influences the quasi-linear flow behavior of rods.
                      It is found that, not unlike polymers, rods of finite
                      stiffness possess a relaxation time spectrum, see section
                      5.5.Extensional flow measurements are conducted to
                      demonstrate the effect of flexibility in the highly
                      non-linear flow regime, see section 5.4. It is found that an
                      increase in particle flexibility leads to a decrease in
                      extensional viscosity. The Trouton ratios of rodlike systems
                      are shown to be comparatively large despite of low normal
                      stresses.In section 5.6, it is demonstrated that the zero
                      shear behavior of polydisperse rodlike particle suspensions
                      does not involve higher complexities, while the shear
                      thinning behavior becomes very complex and, therefore,
                      cannot be understood by employing linear mixing rules in the
                      governing equations for particle dynamics.Finally, it is
                      shown in section 5.7 that a high enough length of rods is
                      crucial for a gradient shear banding transition to occur.
                      Also, it is demonstrated that none of the systems under
                      investigation undergo stable gradient shear banding.},
      cin          = {ICS-3},
      cid          = {I:(DE-Juel1)ICS-3-20110106},
      pnm          = {551 - Functional Macromolecules and Complexes (POF3-551) /
                      DiStruc - Directed Colloidal Structure at the Meso-Scale
                      (641839)},
      pid          = {G:(DE-HGF)POF3-551 / G:(EU-Grant)641839},
      experiment   = {EXP:(DE-MLZ)KWS2-20140101},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/860717},
}