The fluid resistance of single micrometre-sized blank and DNA-grafted polystyrene microspheres under shear flow is compared in purified water and dilute λ-DNA solutions by means of optical tweezers experiments with a high spatial (±4 nm) and temporal (±0.2 ms) resolution.
The measurement results show that the drag experienced by a colloid in a dilute λ-DNA solution (molecular weight of 48502 bp per molecule, radius of gyration of 0.5 μm) is significantly decreased if the microsphere bears a grafted DNA brush. This newly discovered drag reduction effect is studied for different parameters, comprising the molecular weight of the grafted DNA molecules (250 bp, 1000 bp and 4000 bp), the concentration of the λ-DNA solution (11, 17 and 23 μg ml-1, all being significantly smaller than the critical entanglement concentration ), the microsphere core diameter (2 μm, 3 μm and 6 μm) as well as the flow speed of the medium (10 to 50 μm s-1).
The maximum extent of the drag reduction is found to amount to compared to the λ-DNA-induced contribution on the drag acting on blank colloids. We propose a theoretical explanation of this effect based on the combination of the drift diffusion model of Rauscher and co-workers [*c60 20%2] and the stagnation length theory of polymer brushes, as it was established by Kim, Lobaskin el al. . In particular, the solution of the Stokes equation (i.e., the Navier-Stokes equation for creeping flow) for the studied system yields a numerical prediction that is found to be in full accord with our experimental results within measurement uncertainty.
 Ueberschär O, Wagner C, Stangner T, Kühne K, Gutsche C, Kremer F. Polymer 52:4021-4032 (2011)
 Rauscher M. J. Phys.: Condens. Matter 22:364109 (2010)
 Kim YW, Lobaskin V, Gutsche C, Kremer F, Pincus P, Netz RR. Macromolecules 42(10):3650-3655 (2008)
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This poster was presented at the 10th International Symposium on Scanning Probe Microscopy & Optical Tweezers in Life Science, 6-7 October 2011
Olaf Ueberschär a,*, Carolin Wagner a, Tim Stangner a, Konstanze Kühne b, Christof Gutsche a and Friedrich Kremer a
a Institut für Experimentelle Physik I, Universität Leipzig, Linnéstraße 5, 04103 Leipzig, Germany
b Molecular Oncology, Medical School, Universität Leipzig, Semmelweisstraße 14, 04103 Leipzig, Germany
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