Regensburg 2007 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 31: New Materials
CPP 31.7: Talk
Friday, March 30, 2007, 12:00–12:15, H40
Magnetorheology of polymer bottle brushes — Robert Krauss1, Birgit Fischer1, Youyoung Xu2, Axel Müller2, and •Reinhard Richter1 — 1Experimentalphysik V, Universität Bayreuth, D-95440 Bayreuth — 2Makromolekulare Chemie II, Universität Bayreuth, D-95440 Bayreuth
By dispersing polymer bottle brushes [1] in a magnetic liquid synthesized in paraffine oil we are creating a new type of inverse ferrofluid [2]. The brushes differ in their cylindrical symmetry, their semi flexible nature and their ramified nano structure from the compact, spherical objects commonly immersed in ferrofluid [3]. The properties of the new magnetorheological fluid are studied by oscillatory measurements of the storage and loss moduli for varying magnetic induction B. For moderate B < Bc ≈ 10 mT the storage modulus is hardly affected, whereas for larger B we observe a logarithmic increase. The threshold Bc may be interpreted as the percolation transition of a magnetic field induced network of bottle brushes, connecting the bottom with the top plate. Chain formation of the brushes is corroborated by the magnetic field dependent shear thinning observed in rotational measurements of the viscosity. [1] M. Zhang, A. H. E. Müller, J. Polym. Sci. Part A: Polym. Chem. 43, 3641 (2005). [2] A. T. Skjeltorp, Phys. Rev. Lett. 51, 2306 (1983). [3] R. Saldivar et al., J. Chem. Phys. 125, 084907 (2006).