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キーワード:
Colloidal particle; Nematic liquid crystal; Defect topology; Poiseuille flow; Microfluidics; Nonequilibrium molecular dynamics simulation
要旨:
We present nonequilibrium molecular dynamics simulations of a spherical colloidal particle with a chemically homogeneous surface immersed in a nematic liquid-crystal host phase. This setup is then placed between planar and atomically structured substrate surfaces that serve to fix the nematic far-field director . The substrates are separated by a sufficiently large distance such that they do not interfere directly with the environment of the colloid. Because of a mismatch between and the local homeotropic anchoring of molecules of the liquid crystal (i.e., mesogens) at the surface of the colloid circular defect (Saturn) rings ℓ arise if the host is in thermodynamic equilibrium (i.e., in the absence of flow). The size of these rings depends on the range of the mesogen–colloid interactions which we model via an attractive Yukawa potential. As Poiseuille flow is initiated, ℓ is deformed. The degree of deformation is analysed quantitatively in terms of characteristic geometric parameters fitted to suitable projections of ℓ. Our results suggest that smaller ℓ are shifted downstream while approximately maintaining their circular shape, whereas larger ones exhibit an elastic deformation in addition. We provide a simple geometric argument to predict the downstream shift of smaller, circular ℓs in excellent agreement with the simulation data over the range of steady-state flows considered.
