Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: Poster: Biopolymers and Biomaterials

CPP 9.9: Poster

Montag, 14. März 2011, 17:30–19:30, P2

Forces of Interaction between Blank, Grafted and Blank-Grafted Colloids by Using Optical Tweezers — •Tim Stangner, Christof Gutsche, Mahdy M. Elmahdy, and Friedrich Kremer — Institut für Experimentelle Physik I, 04103 Leipzig, Deutschland

Optical tweezers are experimental tools with extraordinary resolution in positioning (+/- 1 nm) a micron-sized colloid and in the measurement of forces (+/- 50 fN) acting on it - without any mechanical contact. Here, we report the direct measurements of the interactions between blank, grafted and blank-grafted colloids across three types of salts different in their valence (KCl, CaCl2, and LaCl3). The forces are repulsive at all measured distances in all three cases, decaying with distance and showed valency dependence. For the symmetric blank colloids (SiO2), the experimental data are well described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory revealing that the effective colloidal charge decreases with increasing counterions valence. In the case of symmetric grafted colloids (SiO2 grafted with poly(acrylic acid)), the data are quantitatively described by the Jusufi et. al. model for spherical polyelectrolytes brushes which takes into account the entropic effect of the counterions. In the asymmetric case (blank against grafted) the experimental data are described by Alexander de Gennes model which only takes into account the steric force.