PSSM Workshop on Liquid Crystals and Colloidal Dispersions
Repulsive interaction between spherical polyelectrolyte brushes as measured by the kinetics of coagulation
Matthias Ballauff, University of Bayreuth, Physical Chemistry I
Abstract: We propose a new way to determine weak repulsive forces operative between colloidal particles by measuring the rate of slow coagulation. As shown by Smoluchowski in his classical papers, the rate of slow coagulation is directly related to the competition of the repulsion with thermal motion. Since the thermal forces are weak, measurements of the coagulation rate can lead to precise information on repulsive potentials having a magnitude of just a few kT. We demonstrate this novel way by studying colloidal spherical polyelectrolyte brush (SPB) particles in aqueous solution containing trivalent La3+ counterions. The particles consist of a monodisperse polystyrene core of 121 nm radius from which linear sodium poly(styrene sulfonate) (PSS) chains are densely grafted (contour length: 48 nm). We determine the rate of coagulation by time-resolved simultaneous static and dynamic light scattering in presence of LaCl3 (0.2 mM to 150 mM). Direct measurements of the repulsive force between macroscopic brush layers demonstrate that the potential is decaying exponentially with distance. This is in good agreement with a simple theoretical treatment that furthermore leads to the effective surface potential. The good agreement of data obtained by the novel microscopic method with direct macroscopic measurements underscores the general validity of our approach.
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Important Dates
| June 10, 2009: | Final Program |
| June 22, 2009: | PSSM Workshop |
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