Regensburg 2007 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
SYPE: Symposium Polyelectrolytes
SYPE 1: Polyelectrolytes Poster
SYPE 1.3: Poster
Mittwoch, 28. März 2007, 16:00–18:30, Poster B
Experiments with single colloids — •Kegler Kati1, Gutsche Christof1, Salomo Mathias2, and Kremer Friedrich1 — 1PAF, Exp. Physik 1, Universität Leipzig, Linnestr.5, 04103 Leipzig — 2Biophysik, Universität Leipzig, 04103 Leipzig
In rheological experiments the flow resistance of single blank or DNA-grafted colloids is determined by Optical tweezers and compared. The degree of swelling of the grafted DNA is adjusted by exchanging the ion concentration of the surrounding medium. For all examined flow velocities one observes an interesting deviation from Stokes law which can betraced back to a shear-dependent conformational change of the brush layer.The ratio of the effective hydrodynamic radii of DNA-grafted and blank colloids shows a pronounced dependence on the flow velocity, but as well on the length of the grafted DNA and the ionic strength of the solvent. The experimental findings are in qualitative agreement with hydrodynamic simulations based on an elastically-jointed chain model. Optical tweezers are employed to measure the forces of interaction between single DNA-grafted colloids. Parameters to be varied are the length of the DNA,the grafting density and the ionic concentration of the surrounding medium. From the measured force-separation dependence an interaction-length at a given force is deduced. It shows in the mushroom regime a scaling with the grafting density which levels off for brushes. For the latter the transition from an osmotic to a salted brush can be traced in detail by varying the ionic concentration in accordance with meanfield theories.