Berlin 2015 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 4: Colloids and Complex Liquids I (joint CPP/DY/BP)
BP 4.3: Vortrag
Montag, 16. März 2015, 10:00–10:15, C 130
Active microrheology of a nematic Liquid crystal — •Tillmann Stieger1, Andrés Córdoba2, Marco G. Mazza3, Juan J. de Pablo2, and Martin Schoen1 — 1Technische Universität Berlin — 2University of Chicago — 3MPIDS Göttingen
The knowledge of rheological properties of soft matter is of great importance for a variety of applications such as lubricants or the reduction of friction. The rheology of materials becomes particularly relevant if systems are miniaturized to the nanometer length scale at which physical properties of soft matter are altered significantly from their microscopic bulk properties. The focus of this work are nematic liquid crystals (LC) which are characterized by a high degree of orientational order along a specific direction. If now a colloid is immersed into such a nematic host phase properties of the later are effected greatly at the nanoscale. The colloid perturbs orientational order of the nematic LC in its vicinity. This causes defect topologies to arise. We present nonequilibrium molecular dynamics (MD) simulations of a homogenous colloid with either planar or perpendicular anchoring of LC molecules at the colloid’s surface. This leads to well known defect topologies such as the Boojum defect or the Saturn ring. The colloid is moved periodically, comparable to a typical experimental setup where one uses optical tweezers. The phase shift and the magnitude of the measured force response is used to investigate viscoelastic properties of the LC host phase. Specifically, we are interested in calculating the dynamic modulus G = G′ + iG″, where G′ and G″ are storage and loss moduli. For both quantities we present analytic expressions that can be used to analyse our MD data.